ramé-hart instrument co.
DROPimage
®
PROGRAM
FOR
CONTACT ANGLE MEASUREMENTS
BY
IMAGE ANALYSIS
Standard Edition
By
Finn Knut Hansen
Professor of Chemistry
University of Oslo, Norway
DROPimage Page 2
Proprietary Notice
The software described in this document is a proprietary product of Finn Knut
Hansen and is marketed under an exclusive agreement with ramé-hart
instrument company. It is furnished to the user under a license for use as
specified in the license agreement.
Information in this document is subject to change without notice end does not
represent a commitment on the part of Finn Knut Hansen or ramé-hart
instrument co. No part of this document may be reproduced, transmitted,
transcribed, stored in any retrieval system, or translated into any language without
the express written permission of Finn Knut Hansen and ramé-hart instrument
co.
Trademarks
DROPimage is a trademark of Finn Knut Hansen. All other trademarks and
registered trademarks mentioned in this document are the property of their
respective owners.
Disclaimer
Finn Knut Hansen and ramé-hart instrument co. take no responsibility for
consequences of errors in the program files or manual and cannot be held
responsible to any physical or economical damage that may result from use of the
program, manual or supplied media.
Note
In MS Windows XP and especially in Windows Vista the visual style will
influence the appearance of icons, buttons, etc. The look of many of these
elements may therefore be different from what is shown in this guide. The
function of the interface is, however, the same.
Copyright  1990-2008 Finn Knut Hansen. All rights reserved
Printed in the USA
DROPimage Standard User’s Guide 2.4
DROPimage Page 3
INDEX
INTRODUCTION ...................................................................... 5
PROGRAM FEATURES .......................................................... 6
ON-SCREEN AND REAL-TIME IMAGE DISPLAY................ 6
TABULAR DISPLAY OF ALL RESULTS ................................ 6
CALIBRATION ........................................................................... 7
CONTACT ANGLE MEASUREMENTS ................................... 7
SURFACE ENERGY TOOLS ..................................................... 7
DROP DIMENSIONS .................................................................. 7
DATA EXCHANGE WITH OTHER PROGRAMS ................... 8
ONLINE HELP ............................................................................. 8
USER GUIDE ........................................................................... 9
STARTING DROPIMAGE .......................................................... 9
HOW TO EXIT............................................................................. 9
SELECTING FUNCTIONS ......................................................... 9
THE MAIN WINDOW............................................................... 10
Viewport ............................................................................................. 10
The Cursor Lines ................................................................................ 11
TUTORIALS - STEP BY STEP PROCEDURES...................... 13
Tutorial 1 - How to perform a calibration........................................... 13
Sphere Calibration .................................................................... 13
Horizontal Calibration .............................................................. 14
Tutorial 2 - Making a contact angle measurement.............................. 15
MENUS....................................................................................... 16
File Menu ............................................................................................ 16
Open Picture.............................................................................. 16
Save Picture............................................................................... 17
Open Profile-data File .............................................................. 17
Save Profile-data File ............................................................... 18
Exit ............................................................................................ 18
Edit Menu ........................................................................................... 18
Edit Phase data ......................................................................... 18
Options ...................................................................................... 19
Copy Picture .............................................................................. 21
View Menu ......................................................................................... 21
Start/Stop pass-through ............................................................. 21
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Intensity Histogram ................................................................... 21
Measure Distance ...................................................................... 22
Zoom Picture ............................................................................. 23
Video Setup ................................................................................ 23
Erase Plot .................................................................................. 24
Calibrate Menu ................................................................................... 25
Show Calibration....................................................................... 25
Check Calibration ..................................................................... 26
New Calibration ........................................................................ 26
Use New/Present Picture(s) ...................................................... 28
THE TOOLBAR ......................................................................... 29
Open Picture ................................................................................ 29
Save Picture ................................................................................. 29
Contact Angle Tool ...................................................................... 30
Buttons ....................................................................................... 30
The Contact Angle menu bar ..................................................... 31
Pulldown boxes ......................................................................... 34
Run name ................................................................................... 35
Stored Results table ................................................................... 35
Stepping ..................................................................................... 35
Acid Base Tool ............................................................................ 36
Purpose...................................................................................... 36
Procedure .................................................................................. 36
Surface Energy Tool .................................................................... 38
Purpose...................................................................................... 38
Procedure .................................................................................. 38
Work of Adhesion Tool ............................................................... 40
Purpose...................................................................................... 40
Procedure .................................................................................. 40
Zisman’s Plot Tool ...................................................................... 41
Purpose...................................................................................... 41
Procedure .................................................................................. 42
Solid Liquid Liquid Tool ............................................................. 43
Purpose...................................................................................... 43
Procedure .................................................................................. 44
Surface Energy (Multi Liquids) Tool........................................... 45
Purpose...................................................................................... 45
Procedure .................................................................................. 46
One Liquid Surface Energy Tool ................................................. 47
Purpose...................................................................................... 47
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Procedure .................................................................................. 47
Take a Picture .............................................................................. 48
Filter Picture ................................................................................ 48
Update Plot .................................................................................. 48
APPENDIX ..............................................................................49
INSTALLATION ....................................................................... 49
INTRODUCTION
Contact angle measurements are of importance to many processes in the chemical
industry. There is a need for a fast and easy technique with satisfactory accuracy
and reproducibility. Traditionally, goniometer type instruments are utilized
throughout the industry and research laboratories. The ramé-hart Contact Angle
Goniometer has a long tradition as the first of this type of instruments, and was
used in the pioneering work of Zisman. After video imaging facilities in personal
computers have become common, the automated contact angle goniometer has
become popular, as it removes much of the tedious work out of this type of
measurements. The accuracy and reproducibility of contact angle measurements
are also improved, and it also makes possible much faster and timed experiments.
The DROPimage program (Standard Edition) is a subset of the more general
DROPimage Advanced program, developed by professor Finn Knut Hansen at the
University of Oslo. The Standard Edition of the DROPimage program is specially
designed for the measurement of contact angles. It also contains 7 different tools
for the calculation of surface energy variables from contact angles. The tools are
integrated in an easy to use user interface and operate intimately with the contact
angle tool to make these types of calculations fast, easy and reliable.
For those that want fully automatic measurements, plotting facilities, and also the
possibilities to measure interfacial tensions of pendant and sessile drops, the
Advanced Edition of the DROPimage program is recommended.
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PROGRAM FEATURES
The DROPimage program has a number of features that make the procedure of
contact angle and surface energy measurements easy and versatile.
The main measurement capabilities are the following
Type of drops
Sessile
Inverted sessile
Captive bubble
Inverted captive bubble
Type of results
Contact angles of one or both sides of drop
Surface energy of solids
Work of adhesion
Zisman’s plot
Drop dimensions, such as
Height
Width
ON-SCREEN AND REAL-TIME IMAGE DISPLAY
The main window contains the captured or live image that may be turned on and
off. This picture is used to set the baseline and cursor lines for the region of
interest (ROI) for the drop or bubble. The tangents defining the contact angle(s)
and the detected edge are also plotted in this picture as a visual indication of the
correct operation of measurement.
TABULAR DISPLAY OF ALL RESULTS
All results are displayed in tabular form in the program’s Contact Angle window.
The results in this table are “live” data that can be used directly by the Surface
Energy tools. The results can also be saved to a Contact Angle (CA) file or to a
text file, as a report. Saved CA files may be read back into this window.
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CALIBRATION
Because the optical magnification may be changed and adjusted by the goniometer and lens system, calibration of the total magnification in the system is
needed whenever the magnification is changed. Accurate calibration is also of
paramount importance to obtain reliable readings. Because of this, calibrating the
magnification has been made an integrated part of the program. Calibration is
performed by measuring a spherical or cylindrical object that has been accurately
measured by other methods. By using the same data treatment techniques as in the
drop profile detection, the optical and mathematical errors are minimized, given
the diameter of the calibration object is comparable to that of the drop.
CONTACT ANGLE MEASUREMENTS
In a manual goniometer, contact angles are measured by means of a graduated
scale and a crosshair in the optical reticle. This program implements 3 different
methods to calculate contact angles by means of image analysis of a drop. The
default method uses a circular curve fit to a number (adjustable) of the profile
points closest to the base-line and calculates the tangent analytically. The Secant
method uses a specially designed numerical extrapolation at the 3-phase
boundary. In addition there is a linear curve fit method that may be used to
measure linear edges (not drops). Either one or both sides of the drop may be
measured separately, and in the latter case the average and difference are also
calculated.
SURFACE ENERGY TOOLS
DROPimage contains a collection of tools for the calculation of surface energy of
solids from contact angles. These tools have the same functionality as the raméhart Imaging 2001 Tools, but have enhanced error calculation. There are
additional tools that can use the measurement from one single liquid up to the
“Multi Liquid” tool that can use any number of liquids. There is also a tool for the
calculation of the surface energy of high-energy solids by measuring contact
angles of one liquid in another (solid/liquid/liquid). Contact angle (CA) files are
interchangeable between RHI 2001 and DROPimage.
DROP DIMENSIONS
The maximum height and width at the base-line of the drop are calculated from
the experimental profile.
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DATA EXCHANGE WITH OTHER PROGRAMS
Both raw images and processed data in several forms may be exported to other
programs, both through the Windows clipboard and different data files. Video
pictures may be captured and copied to the clipboard or saved to disk. This makes
it possible to export pictures to other applications. After edge detection
(“filtering”) the profile coordinates may be saved as a binary or a text file, ready
to be read by other programs.
Results form contact angle measurements may be stored in special contact angle
files (*.CA) that are used by the surface energy tools. These files are compatible
with the ramé-hart Imaging 2001 software tools and contact angle data may thus
be shared between these and DROPimage.
The results from the calculations may be saved as Log-files. The Log-files are
ordinary text-files that are easily read by other programs.
An additional function on the View menu is the "Intensity histogram". This
generates an intensity map along a number of either horizontal or vertical pixels
and is especially suited to study the intensity level and variations across the
profile for instrument adjustment and/or error investigation.
ONLINE HELP
The program has a built-in help Windows system that contains much of the same
information as this manual. The help system is accessed by the main Help menu,
by pressing F1, and by Help menu options in many dialog windows.
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USER GUIDE
Below is a detailed description of the user interface with menu options and
measurement procedures.
STARTING DROPIMAGE
The DROPimage program is started directly from the Start Menu or the
program’s icon. The program will detect and initialize the camera, and, if present,
the ramé-hart dispenser. If loading of the DROPimage program is attempted at the
same time as another program is using the camera, the camera cannot be
initialized. If this happens, the other program must be closed before attempting to
start DROPimage again.
HOW TO EXIT
You exit DROPimage by selecting File | Exit from the main menu or by pressing
the x in the window’s upper right corner.
SELECTING FUNCTIONS
The program is controlled from the main pull down menus. For some of the main
functions such as loading and saving pictures and starting the different Tools,
speed buttons have been provided.
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THE MAIN WINDOW
The Main Window is shown below and contains the Main menu; the Speed
buttons panel, and the Live or Captured image viewport.
Main
Window with
the Main
menu, Menu
bar, and
captured
image
NOTE: You should not maximize the Main window (so it fills the whole
screen). If you do, some of the dialog windows may fall outside the screen or
behind the Main window, and become invisible (!)
Viewport
When the program starts, either a stationary (saved) or a live image is displayed in
the Main window’s viewport. Only one image may be displayed here at a time.
You switch between the stationary or live image by clicking the Live image box.
The stationary image is not updated automatically; you must press the Take a
Picture (Camera) button to update it. You may then save the picture by selecting
the Save Picture button.
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The Cursor Lines
When making contact angle measurements, different cursor lines will be visible
on top of the Main viewport. The lines appear when the Start button in the
Contact Angle tool window is pressed, and disappear again when the Stop button
is pressed. The location of these lines is essential for proper contact angle
measurements.
There are a total of 4 cursor lines. These are:
1.
2.
3.
4.
Horizontal line
Left vertical line
Right vertical line
Red horizontal line
1. The horizontal line indicates the surface baseline. The line is usually set in the
Contact Angle | Setup dialog window. The line may be moved manually by
the mouse by holding down Shift + Left mouse button. The line may also be
moved by the Up and Down arrow keys.
NOTE: The location of the baseline determines what type of drop is
going to be measured. If the baseline is below the middle of the picture,
an ordinary sessile drop is measured, if the line is above the middle, an
inverted drop is expected (and measured). There are two short red lines
on each side of the picture to indicate the mid-point.
The left and right vertical lines serve as indicators for the edge detection
process. The left line is always visible, as the right line may be switched on an
off in the Contact Angle | Options dialog window. You may change the colors
of the lines in the Options dialog.
2. When only the left line is visible, edge detection starts at the intersection of
the profile with the line, and goes to both sides. The left line is moved by the
mouse, holding down the left mouse button, or by the Left and Right arrow
keys.
3. When the right line is also visible, edge detection is only carried out to the left
of the left line and to the right of the right line. The region between the lines is
disregarded. This may be used to mask the syringe needle, as shown in the
figure below. The right line is moved by the mouse, holding down the right
mouse button, or by Alt + Left and Right arrow keys.
DROPimage Page 12
A contact
angle
measurement using
both vertical
lines to mask
the syringe
needle.
4. The Red horizontal line serves to mask a part of the picture, for instance the
syringe needle, as illustrated in the picture below (or another object). The
program only measures between the baseline and the red line, if present.
The red line is turned on and off in the Contact Angle | Options dialog
window. The red line is moved by the mouse by holding down Ctrl + Left
mouse button.
A contact
angle
measurement using
the horizontal
red line to
mask the
syringe
needle.
DROPimage Page 13
TUTORIALS - STEP BY STEP PROCEDURES
In this chapter, 2 tutorials are given as step-by-step procedures are given for fast
introduction to central functions of the program. The calibration procedure is
described, followed by a description of how to make a contact angle measurement.
For more details in the different steps of the tutorials, see the descriptions in the
Menus and Toolbars sections.
Tutorial 1 - How to perform a calibration
Sphere Calibration
To perform the Sphere Calibration, use the sphere calibration tool, which is a steel
ball bearing glued to a glass slide. The glass slide is mounted vertically, so that the
steel ball is imaged through the glass, and is positioned in the middle of the
picture, as shown below.
Pull down the Calibration Menu, choose New calibration and then Sphere.
You will see the picture of the sphere in the Main window, and the Sphere
calibration dialog box as shown below.
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The Diameter is the size of the sphere taken from the initiation file. If the size is
different, you may enter another number. The Number of runs may be selected for
better accuracy, but often 1 is sufficient. Click the OK button and the number of
runs are performed and the vertical and horizontal pixel size and the aspect ratio
are calculated. The result is presented in the calibration value window shown
below.
Because the video camera has “square pixels”, the aspect ratio will be close to 1.0,
but will often differ slightly because of small inaccuracies in the hardware.
Correcting for this deviation will often be important in order to obtain accurate
surface tension readings
Click OK and the measured values are stored in the DROP.CAL file.
Horizontal Calibration
To perform the Horizontal Calibration, use an even metal tube or metal rod. Do
not use a glass tube or glass rod. The rod is mounted vertically and positioned in
the middle of the picture, as shown below. There must be ample room at both
sides of the rod, and no room at the top or bottom, as shown in this picture.
Pull down the Calibration Menu, choose New calibration, then Horizontal. You
will see the picture of the rod in the Main window, and the dialog box as shown
above. The Diameter is the diameter of the rod taken from the initiation file. If the
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size is different, you may enter another number. The Number of runs may be
selected for better accuracy, but often 1 is sufficient. Click the OK button and the
number of runs is performed and the horizontal pixel size it measured. The
vertical pixel size is calculated from the aspect ratio. The result is presented again
in the Calibration values window. Click OK, and the measured values are stored
in the DROP.CAL file.
Note that this procedure does not alter the aspect ratio.
Tutorial 2 - Making a contact angle measurement
To make a contact angle measurement, the following procedure may be used. The
different dialog widows that are mentioned are described in more detail in
subsequent chapters.
1.
Open the Contact Angle window, if it not already open.
2.
Select the liquid and solid phases from the pull-down boxes in the upper
part of the window. If the solid or liquid you want to measure is not in the
list, new items may be added by pressing the corresponding Add button.
They may also be added and edited by the Phase Editor.
3.
Enter a Run Name. If you want to use the results in the Solid Liquid
Liquid tool, the Run Name box should contain the name of the external
phase.
4.
Select the Setup menu. The Contact Angle Setup dialog appears. From this
dialog you can set the baseline and the black and white intensities that
affect the contrast (also available from the View Menu).
5.
Select the Options menu. The Contact Angle Options dialog appears.
Select the options you want, and close the Options menu. Options will be
kept between experiments.
6.
Click the Start button. The crosshairs cursor lines appear.
7.
If you want to use the Red-line, place the line by Ctrl + Left mouse button.
8.
Focus on the drop, and adjust the Left and/or Right vertical cursors by the
mouse, holding down the left or right mouse button, respectively.
9.
Press Measure. One or more measurements are taken, according to your
Options. The result(s) appear in the Stored Results table.
10. Repeat Measure as many times as you wish.
11. When finished, press Stop (same as the Start button). The crosshair cursor
lines disappear.
12. You can Start and Stop as many times as you wish.
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13. Save the Contact Angle file by selecting Save As on the File menu.
14. You may want to save the data in a text file, by selecting Make Log on the
File menu.
MENUS
The Main menu contains the following sub-menus:
File Menu
Open Picture
Save Picture
Open Profile-data File
Save Profile-data File
Exit
Edit Menu
Edit Phase data
Options
Copy Picture
View Menu
Start/Stop passthrough
Intensity Histogram
Video Setup
Zoom Picture
Calibrate Menu
Show Calibration
Check Calibration
New Calibration
Use New Picture(s)
File Menu
Open Picture
The File | Open picture function restores a bitmap file that was formerly saved by
the File | Save picture function or by a timed measurement with Bitmap storage
selected in the Method.
The speed button
has the same function as the File | Open picture function.
The supported file types are PIC, GIF and BMP
A PIC bitmap picture is read into memory and shown on the screen in the main
window. It may then be further processed by filtering etc.
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A BMP file is also converted to the internal byte format and may be processed in
the same way. This means that DROPimage is able to read BMP files created by
other programs so that DROPimage may be used by a general BMP file viewer.
However, further processing of such pictures by DROPimage will only be
meaningful if these pictures have the same general properties as the DROPimage
pictures (256 colors, black & white, maximum ca 400 kB).
Save Picture
The File | Save picture function saves the bitmap in the memory buffer to a disk
file.
The speed button
has the same function.
The supported file types are those described under Opening a picture, plus the TIF
file format. Files saved in the BMP, GIF or TIF formats may be read by other
programs. This is a convenient way to export pictures for printing, editing etc. The
pictures are in 8 bit black & white format (256 grays).
Open Profile-data File
A file that is saved as a profile-data file (“filtered data”) may be viewed by this
function. The opened profile is displayed in a separate window as shown below.
The numbers in the caption show the size of the bitmap from which the profile has
been determined (Rows x Lines). Note that several bitmap sizes are supported in
addition to the standard 640 x 480 (RS-170) and 768 x 576 (CCIR).
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Save Profile-data File
The File | Save profile-data file function saves the profile-data, either to a standard
profile file (type DAT) or to a text file (type TXT).
The text file does not contain the size information of the original picture or other
key data fields in the same way as the standard profile file. These files are,
therefore, only intended for data export, and they cannot be read back into
DROPimage.
Exit
This exits the DROPimage program. The image in the viewport is lost, if not
saved prior to exit. The contact angle data in the Contact Angle window’s table
are saved and restored the next time the program is started.
Edit Menu
Edit Phase data
In order to maintain the two files liquids.txt and solids.txt that are used in the list
boxes in the Contact Angle tool window, the Phase editor is convenient.
The function of this editor is mostly self-explanatory. The Name field may contain
up to 255 characters. Total is the total surface tension of the liquid, while Disp.
and Polar are the dispersive and polar components of Total. The Polar+ and Polarvalues refer to the acidic and basic components of the non-Lifshitz-Van der Waals
DROPimage Page 19
components, according to the theory by van Oss and co-workers. The sequence of
substances is the same as in the file, i.e. the data are not sorted.
The files should not be edited in an ordinary text editor (such as Notepad) in order
to avoid formatting errors, but may be imported to and edited in a spreadsheet
program, such as Excel.
Options
Many of the default control parameters for DROPimage many be changed from
the Edit | Options window that is shown below.
Plotting Options
Plot profile in picture: Determines if the profile should be plotted after a filter
operation.
Continuous display: Determines if the picture is updated after each measurement
in an experiment.
Installed Options
This checkbox tells the system if the ramé-hart dispenser is installed in the system.
The program does not check if a device really is present, so if you enable this
option when the device is not present or switched off, the program may stop when
trying to access the device.
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Calculation Parameters
Some of the parameters used in filtering and calculations may be adjusted here.
The parameters are saved between sessions in the DROP.INI file.
The pixel points that are used in the
edge detection (filtering). A total number of 2n+1 points are used, meaning that
when n=7 the total number is 15. Increasing n to a maximum of 20 may improve
the stability of the edge detection algorithm, especially if the edge is not well
defined (less sharp), but will lead to longer filter times. On the other side,
decreasing n to 3 or 4 may improve edge detection of very small drops.
Number of filter points on each side (=n):
The fraction F in the edge
definition (in Equation [1], Appendix 1A). It may be set to any value between 0
and 1 but our experience indicates that values between 0.5 and 0.6 are best. The
value may possibly influence the degree of dependence of magnification on g (g
should be independent of magnification).
Contour definition (fractional intensity) parameter:
is self-explaining. A high number here will
possibly improve the chance of obtaining an optimized value in some instances,
but experience has showed that if this number exceeds 5-6, the quality of the
profile data is bad, meaning the drop is either unsymmetrical, or there is some
other problem.
Maximum number of optimizations
is also used in the optimization procedure. The
procedure will continue until the maximum relative error is subsided, or the
maximum number is exceeded.
Maximum relative error in gamma
is the maximum "noise" difference between two neighbour pixels
that is allowed in the initial determination of the profile start-point. The ‘profile
start’ seeking routine looks along the vertical line of the crosshair cursor. When
the difference between two intensity values is greater than noise filter level, the
program determines that point as the start of the profile. It may therefore be
necessary to adjust this parameter to fit the lighting and general picture conditions.
A value too high or too low may lead to a condition in which the profile is not
found.
Noise filter level
Measurement parameter options
Selects where the Red horizontal line is displayed in the
main picture. This line acts as a mask in order to avoid disturbing objects in the
top or bottom of the picture. If the line is in the upper half of the picture, the part
of the picture above the line will be excluded from all filter operations, if the line
is in the lower half, the part below the line will be excluded. The line may be
Show horizontal mask at:
DROPimage Page 21
moved directly by means of the mouse, by holding down the Ctrl key and the Left
mouse button. The position in the Options window will be changed accordingly.
Color options
The color boxes show the colors of the cursor lines, the plotted profile, and the
plotted contact angle. By clicking the corresponding color box, a dialog window
will open that lets you select the color.
H+L Cursors:
Horizontal and Left lines.
R Cursor:
Right line.
Profile:
Plotted profile.
Cont.angle:
The lines that indicate the contact angles.
Copy Picture
This function copies the image in the viewport to the Windows clipboard (as a
DIB). Pressing Ctrl + C when the image is in the focus, performs the same
function. The picture may then be pasted into other Windows applications, like a
word processor, graphics program, etc.
View Menu
Start/Stop pass-through
This menu item performs the same function as the “Live Image” display checkbox
on the toolbar.
The program’s display window can be turned to “Live Display” by clicking the
check box on the toolbar. The magnification may be changed between 10 and
200% by means of the Zoom function on the View Menu.
Intensity Histogram
An intensity histogram is a bar graph of the intensity values (0-255) of a
horizontal or vertical row of pixels. This function may be useful in the setup and
adjustment of the optical system and in error detection (to check where the
intensity change has its maximum). When the function is selected, a picture is
«taken» as described above, and the white crosshair cursor is shown in the middle
of the picture. This may be moved by means of the mouse and arrow keys as
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outlined in the measurement section. The histogram contains 15 bars with the coordinates of the cursor (crosshair) as midpoint and is updated continuously
whenever the cursor is moved. An example of a histogram is shown below.
The x-axis of the histogram initially corresponds to the horizontal direction in the
picture, but this may be changed to the vertical direction by selecting the Vertical
radio button. If a picture is presently visible on the screen, a new picture is not
taken, meaning that a picture that is loaded from a file may also be analyzed in
this way.
Measure Distance
Sometimes it is desirable to measure one or more distance/dimension in a picture.
For this purpose the Measure tool is very useful. The tool is available on the
Measure menu and is shown below.
When the tool is opened, two red crosses appear in the picture. The default
position is in the upper left corner. The crosses are moved by clicking with the
left and right mouse buttons, and the pixel positions are displayed, as well as the
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distance between the crosses (in mm). To calculate the distance, the current
calibration is used.
When the tool is closed, the crosses disappear. You can measure both in a live
video image and a static picture. You are not allowed to measure during an
experiment, when the line cursors are visible. The picture can also be loaded from
a file, but it should be remembered that the calibration of loaded pictures should
be the same as the current one.
Zoom Picture
In order to keep the correct aspect ratio the captured image cannot be sized by
grabbing its borders or corners, however, the image may be sized by the Zoom
picture function. This menu item has a submenu where you can select 200%, 100%,
75%, 50% or Other... The 100% magnification means that one image pixel is one
pixel on screen, the other magnifications are relative to this. If you select Other...,
the dialog shown below appears.
The slider may be used to set a scale between 0 and 200%, in steps of 10%. The
scale will be remembered between sessions. If the image is too big for the main
window, scrollbars will appear.
Video Setup
In the Video Setup dialog you can select the Video Device (camera) to be used by
the program and one of the supported Media Types. The Video Device can be
selected among the installed video cameras that have a DirectDraw supported
driver. In a standard ramé-hart installation, you will only have one camera visible
in this pull-down list. The camera has to have a WDM (Windows Driver Model)
driver to be visible in this list. The Media Types listed in the Active Media Type
pull-down list are dependent on the media types supported by the camera driver.
The formats listed usually are the color format, the resolution, and the number of
bits used by that format. The program will adjust itself automatically to the listed
format(s). If the camera supports color, the program will show color still images
if Color is selected in the Input Video Format group. Note: Acquired images will
DROPimage Page 24
always be saved and processed in 8 bit black & white format (grey scale),
whatever the format listed in the Active Media Type and even if Color is
selected in Input Video Format. The DROPimage program does not support the
saving of color pictures.
The Video Properties and Capture Properties buttons bring up the camera driver’s
property pages for the selected Active Video Device. In these property pages, you
can adjust many settings of the camera, such as intensity, contrast, frame rate, etc.
The property pages are camera dependent and are therefore further described in
the additional Camera Guide for your camera. For some camera/driver
combinations the frame rate setting in the Capture property page will not work
properly; in that case the Frame Rate button will bring up a box in which the
frame rate can be set. You can write anything into this box, but the driver will
only return with the nearest possible frame rate, or the default rate (often 15 fps).
Sometimes the frame rate cannot be changed with this function (driver
dependent). The program will remember the frame rate between sessions.
If the Capture Properties button is disabled (grayed), the capture property page is
not available (usually because it doesn’t work properly).
If you change the Active Media Type (and possible also the Active Video
Device), you must click on the Restart button to activate the changes. The
DirectDraw Filter Graph will then restart. When installed, the program may have
selected the first Video Device and first Media Type it can find, and a message
will appear stating this. You should then set the Video device and Media Type
you want to use and the program will remember those settings, until further
changes have been made. If you ever change the camera, this procedure must be
repeated.
Erase Plot
Erases all lines and objects plotted in the picture
DROPimage Page 25
Calibrate Menu
In order to calculate correct surface tensions, the magnification of the video picture must be known. By calibrating, the program measures a known object, and
the size of the pixels in the vertical and horizontal direction are calculated
automatically.
The calibration procedure must be performed every time the magnification of the
optical system is changed. When DROPimage is started the last calibration is
automatically restored (this is stored in the file DROP.CAL). Measuring the
diameter of a cylinder placed in the camera’s view usually performs calibration. A
cylinder, a steel or glass bar or tube may be used. This object must be measured
accurately by some other method (for instance a micrometer gauge).
The Calibration menu contains 4 choices:
Show Calibration
Check Calibration
New Calibration
The last choice is Use new picture(s)/Use present picture, which makes it possible
to use a saved picture (e.g. from another computer) for calibration.
For a detailed description on how to perform a calibration, see the chapter How to
perform a calibration.
Show Calibration
The Show calibration menu option just shows the Calibration values window.
It is possible to adjust the aspect ratio in this dialog. By clicking the Adjust Horiz.
button, the horizontal pixel size is calculated from the vertical pixel size and the
(new) aspect ratio.
You cannot change the vertical and horizontal pixel sizes directly in this dialog.
DROPimage Page 26
Check Calibration
This function is used for quality assurance purposes. You may by this function
compare the calibration values with those already stored. It is thus possible to
make certain that measurements made with the current calibration are correctly
calibrated. If they are not, you should make a new calibration in the usual way.
This tool uses the Sphere Calibration method in order to check both magnification
and aspect ratio. You will see the picture of the sphere in the Main window, and
the following dialog box:
The Diameter is the size of the sphere taken from the initiation file. If the size is
different, you may enter another number. The Number of runs may be selected for
better accuracy, but often 1 is sufficient. Click the OK button and the number of
runs are performed and the vertical and horizontal pixel size and the aspect ratio
are calculated. The result is presented in the calibration value window shown
below. When calibration is finished, the Check calibration values window is
shown in a special dialog:
The current (Stored) and measured (New) values are displayed, together with the
% deviation. You can then determine if the present calibration is satisfactory (the
values shown above are results from a manual adjustment of the aspect ratio, as
described under New Calibration).
New Calibration
This submenu contains 2 choices
DROPimage Page 27
Horizontal means that the (horizontal) width of a vertical cylinder is measured.
The Sphere calibration is intended for measuring a spherical object, freely visible
in the picture. When one of the menu options is selected, the picture of the object
is shown above the calibration start window.
The Diameter is the width of the object and the value is taken from the initiation
file, however, another Diameter may be entered if desirable. The Number of runs
may be set at more than 1 for an even better accuracy. When the OK button is
clicked, the “number of runs” diameters are measured and an average value is
used for calculation of the pixel size. The result is presented in the calibration
value window.
In a horizontal calibration the horizontal pixel size is measured and the vertical
pixel size is calculated from this value and the aspect ratio. A new horizontal
calibration must be performed if the magnification of the system is changed.
When calibration is finished, the Calibration values window is shown as described
under Show Calibration.
In a sphere calibration, both pixel sizes and the aspect ratio are calculated. This
seems to be the best method for calibration. The whole sphere must be visible in
the picture, and no disturbances present along the sphere surface (any suspending
wire) (see How to perform a calibration). Good results are obtained by using a
steel ball bearing sphere glued onto a glass plate (a microscope slide). The glass
plate is placed vertically with the sphere close to the midpoint of the picture.
Also for this function, the default sphere diameter is taken from the initiation file.
The program will determine the complete profile of the sphere, and calculate the
vertical and horizontal pixel size and aspect ratio (horizontal/vertical) from 2nd
degree polynomials fitted to the 4 extreme regions (upper, lower, left, right).
However, experience has shown that the aspect ratio calculated by a sphere
calibration may not be the best in all situations; therefore it is possible to make
small adjustments of this ratio manually. The best value is usually found when the
DROPimage Page 28
surface tension does not change with drop size, and a pendant and sessile drop of
the same liquid gives the same surface tension (this may still not be obtainable in
all situations, for different reasons).
Use New/Present Picture(s)
This switch selects if calibration is done on one or more new pictures from the
camera, or on the picture already shown.
is the normal (default) mode, and calibration will be performed
as described in How to perform a calibration
Use new picture(s)
If the switch is clicked, the text will read Use Present Picture. This allows for
calibration from saved pictures (all supported formats) and makes it possible to
calculate experiments done with another system, if a calibration image is available
for that system.
DROPimage Page 29
THE TOOLBAR
The speed-button toolbar makes easy access to the most important tools of
DROPimage.
The speed-buttons are described below
Open Picture
This button has the same function as the Open Picture… line on the File menu.
Save Picture
This button has the same function as the Save Picture… line on the File menu.
DROPimage Page 30
Contact Angle Tool
This button opens the Contact Angle window. The window is shown below.
The Contact Angle tool window has its own menu bar at the top.
When taking measurements, contact angle results appear at the bottom in the
Stored Results table. The results are also written to an internal file that is saved
between sessions. The results in this table always show the “active” contact angle
data. Operations on this table are reflected in the active data and vice versa.
Opening a contact angle file on this tool or any other contact angle tool will add
the results to this table and to the active data. The three buttons directly below the
table operate on the data in the table and on the active data.
Buttons
Clear All
Deletes all data in the table and all active data. You should save the data before
you clear it if you want to keep some of the results.
DROPimage Page 31
Delete
You can select one of more consecutive lines in the table with the cursor. The
Delete button will remove these lines.
Change
The active data always contain information on the Liquid(s), Solid, and the Run
name. When you select a line in the table, the text in the boxes at the top changes
to reflect the active data record. This information does not change for measured
data even if you change the text boxes. However, by clicking the Change button,
the active data for the selected line(s) is also changed. This may be a useful tool in
case you forgot to select the correct liquid or solid, or if you wish to change the
Run name. Note: The changes are not made to permanent data on file. You have
to save the data (again) if you want to change it permamently.
Close
Closes the Tool window.
Start
Starts one or more measurements. The Crosshair cursor becomes visible, and the
Measure button becomes active. The text of the Start button changes to Stop.
Another click on the Stop button reverses this action and hides the crosshair
cursor again. Some menu items will also be deactivated as long as Measure is
active.
The Contact Angle menu bar
File
Open
Opens a Contact Angle (CA) file and adds the data to the bottom of the Stored
Results table.
Save As
Saves all the data in the Stored Results table to a Contact Angle (CA) file.
Generate Log
Saves all the data to text file. The file extension is TXT.
DROPimage Page 32
Options
Opens the Contact Angle Options dialog.
The Contact Angle options dialog window is used to set the basic control
parameters for the measurement(s). The Contact Angle options are remembered
between runs.
If the Number of Measurements is more than 1, the Time Interval is used between
each measurement. If Time Interval is below 0.04 s, the frames are acquired as
fast as possible.
sets the number of frames used as an average in each
measurement. The frames are acquired as fast as possible, usually 30 (U.S.,
Japan), or 25 (Europe, etc.) frames/sec. This averaging should not be confused
with the Number of Measurements. The total number of frames acquired is the
Number of Measurements x Frame Averaging.
Frame Averaging
selects measurement of captive bubbles. The contact angle will be
calculated as the outside angle (in the liquid).
Captive Bubble
selects the measurement of a oil in water or water in oil system.
When this box is checked, a new drop-down box appears in the Contact Angle
tool. The box, named Ext.phase, is used to select the external phase. Two liquids
are used in the Solid Liquid Liquid Surface Energy tool.
Two Liquids
Use Right Cursor
turns on and off the Right vertical line.
turns on and off the horizontal Red-line. This line limits the Region
Of Interest (ROI) for the measurement.
Use Red Line
DROPimage Page 33
In the Measure group box the actual picture and angle(s) are set. If Present picture
is selected, the picture already in the Main window is used. This makes it possible
to measure saved pictures.
In Angle Options you select which angle(s) is/are to be measured.
The Method group selects which extrapolation method to use for the contact angle
calculation:



The Circle method, which is the default, will normally be the best.
The Secant method (used by the original DROPimage program) uses an
extrapolated secant, and may be better for very large drops, where the edge
deviates much from circularity.
The Line method uses a straight line fit, and is only to be used to measure
straight edges (not drops), for instance for tilt angles.
Setup
Opens the Contact Angle Setup dialog.
The Contact Angle Setup dialog window is used to set the baseline and/or contrast
for the measurement(s).
When the Setup dialog shows, all 3 cursor lines (horizontal, left and right) will
appear in the Main Window. The two vertical cursor lines will appear close to the
edges of the image. The two Intercept boxes in the Setup dialog show the intercept
between these two lines and the horizontal line. The Baseline box shows the
location of the baseline. All values are given in pixels from the top.
The Tilt indicator measures the tilt of a line through the two intercepts (the tilted
line is NOT shown). You can adjust the left and right cursor by the mouse,
holding down the left or right button, respectively. The objective is to adjust the
image to obtain the minimum (i.e. close to zero) tilt. The tilt will usually be
DROPimage Page 34
adjusted by either adjusting the Goniometer’s stage, the sample, or the camera tilt
(if the stage is already horizontal).
The Snap button moves the horizontal line to the mid-point between the two
intercepts.
The tilt measured may also be dependent on the image’s contrast. Thus, the
contrast is shown by the Contrast indicator. Contrast may be adjusted by the
camera’s property page in the Video Setup dialog (see the View menu) that may
also be opened from this window.
All intercepts are calculated by the maximum gradient method.
Pulldown boxes
The pulldown combo boxes contain the name of the liquid and solid. The names
are taken from the files LIQUIDS.TXT and SOLIDS.TXT, respectively. A new
liquid or solid may also be added by clicking the corresponding Add button. This
brings up the Add dialog:
You must add at least the name of the liquid (or solid) and the Total surface
tension. The other surface tension components are only necessary for liquids,
dependent on which of the surface energy tools that are being used. The Polar+
and Polar- values are only used by the Acid Base Tool.
These parameters may also be added and/or edited by the Phase Editor.
DROPimage Page 35
Run name
The run name is voluntary and is only used to identify the experiment. In the case
the Solid Liquid Liquid (SLL) Tool is going to be used with the contact angle
data, the Run name box should contain the surface tension of the liquid (however,
it is possible to enter the surface tension later, in the SLL Tool).
Stored Results table
The table is filled with the results, sequentially. The Delete button is used to delete
the item under the cursor, and the Clear All button clears the whole table. Contact
angle files that are loaded into the program, are appended to the bottom of the
table. The data in the table are saved between runs in a special file.
Stepping
If the ramé-hart dispenser is present in the system, the lower part of the Contact
Angle tool window will contain an extra button denoted Steps:
When the button is pressed, the lower part of the window is expanded. The two
Stepping buttons are initially greyed, but are activated when the Start button is
pressed. The lower part of the window then looks as shown below:
The two buttons are self-explanatory, and are intended for the measurement of
advancing and receding contact angles, as denoted in the group box’s caption. The
Delay time is the time (in milliseconds) between the (start of the) actual step and
the measurement. The measurement uses the values of the Number of
measurements and Frame averaging in Contact Angle options at each step.
DROPimage Page 36
Acid Base Tool
Purpose
The ‘Acid-Base Tool’ evaluates the surface energy parameters of a given solid
using the contact angles of three different test liquids. Van Oss et al have shown
that the contribution due to acid-base interactions can be expressed in terms of the
product of their electron donor and electron acceptor components by using three
liquids, one apolar and two polar. Recommended test liquids are methylene iodide
or bromonaphthalene for the apolar liquid and a polar liquid pair of either water
and glycerol or water and formamide.
Reference:
1. C.J. van Oss, R.J. Good and M.K. Chaudhury; Adv. Colloid Interface Sci. 28,
35 (1987).
2. C.J. van Oss, R.J. Good and M.K. Chaudhury, J.; Chromatography 191, 53
(1987).
3. C.J. van Oss, R.J. Good and M.K. Chaudhury, J.; Langmuir 4, 884 (1988).
Procedure
This is a step by step procedure of how to use the Acid-Base Tool:
Step 1. Open the Acid-Base Tool.
DROPimage Page 37
Step 2. Select File | Open from the Acid-Base Tool’s menu and open one or more
files generated by the Contact Angle Tool or from RH Imaging 2001 (denoted by
the *.CA extension), or use the data already in the Contact Angle Tool. In this
example the PARAFILM.CA file is used. If one or more files are already opened
in the Contact Angle File Control, the new records are added to those already
present. All active data are shown in the Contact Angle File Control.
Step 3. Select the desired Solid, Liquid 1, Liquid 2, and Liquid 3 from the drop
down lists.
Step 4. The surface energy measurements are automatically calculated when the
appropriate solid and liquid combinations are selected. The results are displayed in
the Surface Energy of Solid section.
The Close button closes the window, but keeps the live data.
The Reset button erases all live data, but does not close the window.
The Recalc button is used for experimenting with contact angle values and/or
using values measured by other methods/programs. Numbers different from those
automatically calculated may be entered in the Average Contact Angle boxes.
Clicking the Recalc button will then calculate the resulting surface energies.
DROPimage Page 38
Surface Energy Tool
Purpose
The ‘Surface Energy Tool’ evaluates the surface energy of a given solid using the
contact angles of two different test liquids.
The geometric-mean method uses two pure liquids denoting their dispersive and
non-dispersive values. Water and methylene iodide are a convenient choice for
test liquids. Different liquid pairs tend to give different results. The surface
energies and polarities of some low-energy solids obtained by this method are
often much lower than those calculated by other methods.
Reference: D.K. Owens and R.C. Wendt, J Appl Polym. Sci. 13, 1741 (1969).
The harmonic-mean method also uses two liquids in its calculations. The results
obtained with this method are regarded as accurate by Wu and agree remarkably
well with other methods. Wu claims that this method is especially suitable for
polymers, but this finding has, however been disputed. Some researchers consider
that non-dispersive interactions across interfaces are mainly of acid-base nature
and in that situation recommend using the acid/base tool. The harmonic-mean
method may not always give a solution, depending on the measured data.
Reference: S. Wu, J Polym. Sci C34, 19 (1971).
Procedure
This is a step by step example of how to use the Surface Energy Tool:
Step 1. Open the Surface Energy Tool.
DROPimage Page 39
Step 2. Select File|Open from the Surface Energy Tool’s menu and open one or
more files generated by the Contact Angle Tool or from RH Imaging 2001
(denoted by the *.CA extension), or use the data already in the Contact Angle
Tool. In this example the PARAFILM.CA file is used. If one or more files are
already opened in the Contact Angle File Control, the new records are added to
those already present. All active data are shown in the Contact Angle File Control.
Step 3. Select the desired Solid, Liquid 1and Liquid 2 from the drop down lists.
Step 4. To calculate the surface energy using the harmonic method, click on the
Harmonic button.
To calculate the surface energy using the geometric method, click on the
Geometric button. The results will be displayed in the Surface Energy of Solid
area.
The Close button closes the window, but keeps the live data.
The Reset button erases all live data, but does not close the window.
It is possible to experiment with contact angle values and/or using values
measured by other methods/programs. Numbers different from those
automatically calculated may be entered in the Average Contact Angle boxes.
Clicking the Harmonic or Geometric button will then recalculate the resulting
surface energies.
NOTE: In the geometric mean method the surface energies are calculated by
solving linear equations in the square root of the energies. In some cases,
especially if the polar component is low, measurement inaccuracy may cause one
of these to become negative, while the square is positive. These values are clearly
in error, and the program will indicate this by changing the color of the result box
to yellow. If this happens, you should reconsider your results.
DROPimage Page 40
Work of Adhesion Tool
Purpose
The ‘Work of Adhesion Tool’ determines an index of wetting ability of a liquid
for a solid. The Adsorption Theory proposes that van der Waals interactions
should be sufficient for good adhesion. The liquid/solid thermodynamic
considerations give rise to this equation relating the reversible work of adhesion
and surface free energies according to Young and Dupre, noting that the process
of adhesion may be described in terms of opposites, namely the process of
separation.
Reference:
Buff, F.P. “The theory of capillarity”, in Encyclopedia of Physics; Flugge, S., Ed:
Springer-Verlag: Berlin, 1960; pp. 281-304.
Procedure
This is a step by step example of how to use the Work of Adhesion Tool:
Step 1. Open the Work of Adhesion Tool.
Step 2. Select File|Open from the Work of Adhesion Tool’s menu and open one
or more files generated by the Contact Angle Tool or from RH Imaging 2001
(denoted by the *.CA extension), or use the data already in the Contact Angle
Tool. In this example the PARAFILM.CA file is used. If one or more files are
already opened in the Contact Angle File Control, the new records are added to
those already present. All active data are shown in the Contact Angle File Control.
Step 3. Select the desired Solid and Liquid from the drop down lists.
DROPimage Page 41
Step 4. The work of adhesion measurement is automatically calculated when the
appropriate solid and liquid combination is selected.
The Close button closes the window, but keeps the live data.
The Reset button erases all live data, but does not close the window.
Zisman’s Plot Tool
Purpose
The ‘Zisman’s Plot Tool’ summarizes wetting behavior and allows predictions of
an interpolative nature using a homologous series of liquids. Extensive series of
measurements of contact angles of various liquids on low-energy polymer
substrates were reported by W.A. Zisman, inventor of the ramé-hart Contact
Angle Goniometer, and his coworkers at the Naval Research Laboratory. An
empirical linear relation was found between the cosine of the contact angle and the
surface tension of the liquid of the sessile drop. The extrapolation of the line to
cos() = 1 gives the “critical surface tension” of the substrate.
DROPimage Page 42
The term “critical” is used because any liquid on the Zisman plot whose surface
tension is greater than the “critical surface tension” makes a finite contact angle
with the substrate. Critical surface tension values are useful empirical values that
characterize relative degrees of surface energy of polymer substrates. Zisman’s
empirical prediction fails for liquids that form hydrogen bonds or acid-base
interactions with the substrate. These liquids would spread spontaneously on the
substrate.
Reference: W.A. Zisman, ACS Adv. Chem. Ser. 43, 1 (1964).
Procedure
This is a step by step example of how to use the Zisman’s Plot Tool:
Step 1. Open the Zisman’s Plot Tool.
Step 2. Select File|Open from the Zisman’s Plot Tool’s menu and open one or
more files generated by the Contact Angle Tool or from RH Imaging 2001
(denoted by the *.CA extension), or use the data already in the Contact Angle
Tool. In this example the PARAFILM.CA file is used. If one or more files are
already opened in the Contact Angle File Control, the new records are added to
those already present. All active data are shown in the Contact Angle File Control.
Step 3. Select the desired Solid and Liquid from the drop down lists. Click on the
Add to Graph button. Select a second Liquid and click on the Add to Graph
button. Two or more solid/liquid combinations must be chosen in order for points
to be plotted on the graph.
Note: Click on the Add ALL to Graph button to automatically plot each point on
the graph.
Step 5. The critical surface tension for the given solid is automatically calculated
when two or more solid/liquid combinations have been selected. The error given
is calculated from the Standard Error of the regression in the x-direction at the
critical surface tension.
The Close button closes the window, but keeps the live data.
The Reset button erases the plot and all live data, but does not close the window.
DROPimage Page 43
Solid Liquid Liquid Tool
Purpose
The ‘Solid-Liquid-Liquid Surface Energy Tool’ evaluates the surface energy of a
given solid using the contact angles of one test liquid on a solid submerged in a
series of different liquids according to the method of Shultz et al. According to
this method a plot of W - H + WHcos vs. (Wd)1/2 - (H)1/2 gives a straight line
with the intersection ESW = 2(SpWp)1/2 and slope 2(Sd)1/2. From these values the
surface energy of the solid, Sd (dispersive) and Sp (polar) are calculated. (Here W
denotes the polar liquid, usually water, and H the external unpolar liquid, usually a
hydrocarbon). It is noted that the interfacial tension WH is needed for this
calculation. Mutual solubility between the two liquids may be a problem with this
method.
Water or formamide is usually used as the test liquid and a series of hydrocarbons
as the continuos phase (hexane, cycohexane, octane, decane, hexadecane). At least
2 different liquids must be used. The method is especially useful for high-energy
solids as metals and oxides that are otherwise wetted by most liquids.
Reference:
J.Schultz, K.Tsutsumi and J.-B. Donnet, J.Colloid Interface Sci 59, 272 and 277
(1977)
DROPimage Page 44
Procedure
This is a step by step example of how to use the Solid-Liquid-Liquid Surface
Energy Tool:
Step 1. Open the Solid-Liquid-Liquid (SLL) Surface Energy Tool.
Step 2. Select File|Open from the SLL Surface Energy Tool’s menu and open one
or more files generated by the Contact Angle Tool or from RH Imaging 2001
(denoted by the *.CA extension), or use the data already in the Contact Angle
Tool. In this example the PLATINUM.CA file is used. If one or more files are
already opened in the Contact Angle File Control, the new records are added to
those already present. All active data are shown in the Contact Angle File Control.
The Contact Angle File may contain surface tension data in addition to contact
angles.
Step 3. Select the desired Solid and Droplet Liquid from the drop down lists.
Select one External Liquid and click on the Add to Graph button. Select a second
External Liquid and click on the Add to Graph button. Two or more external
liquids must be chosen in order for points to be plotted on the graph. The
interfacial tension between the Droplet liquid and External liquids may be
included in the Contact Angle file if the file is produced from normal interfacial
tension results (both contact angle and interfacial tension are calculated). If the
interfacial tension is not present in the file, the Interfacial Tension box will
become white, and you must input the interfacial tension in the box.
Note: Click on the Add ALL to Graph button to automatically add all External
Liquids to the graph. This can only be used if ALL interfacial tensions are present
in the file(s).
Step 5. The surface energy for the given solid is automatically calculated when
two or more liquid-liquid combinations have been selected.
The Close button closes the window, but keeps the live data.
The Reset button erases the plot and all live data, but does not close the window.
DROPimage Page 45
Surface Energy (Multi Liquids) Tool
Purpose
The ‘Surface Energy (Multi Liquids) Tool’ evaluates the surface energy of a given
solid using the contact angles of two ore more test liquids. With two liquids it
gives the same result as the Surface Energy (Two Liquids) tool as these two tools
use the same theoretical foundation. When using more than 2 liquids, this tool is
more useful than taking the average value of all possible pairs of liquids. The
method is based on plotting the equation
 cos   1
L
2
 dL
  Sd   Sp
 pL
 dL
The left side is plotted as a function of the right hand fraction and a straight line
fitted through the data points gives the square root of the dispersive and polar
component of the solid’s surface energy.
DROPimage Page 46
Reference: Rabel, W., “Wetting theory and its application to the study and use of
the surface properties of polymers”, Farbe + Lack (1971), 77(10), 997-1006.
The slope of the line can theoretically not become negative, but errors in the
measurements may cause the experimental slope to become negative. If this
happens, the tool will give an error message, in addition the result box for the
polar part of the SE will become yellow. The measurements should in this case be
examined for possible errors (surface roughness may often be the cause of such
errors).
The displayed error limits are the standard deviations calculated from the
regression line and do not take the errors in the contact angles into consideration,
as these are usually lower.
Procedure
This is a step by step example of how to use the Surface Energy Tool:
Step 1. Open the Surface Energy (Multi Liquids) Tool.
Step 2. Select File|Open from the Tool’s menu and open one or more files
generated by the Contact Angle Tool or from RH Imaging 2001 (denoted by the
*.CA extension), or use the data already in the Contact Angle Tool. In this
example the PARAFILM.CA file is used. If one or more files are already opened,
the new records are added to those already present. All active data are shown in
the Contact Angle Tool and the Contact Angle File Control (if open).
Step 3. Select the desired Solid and Liquid from the drop down lists. Click on the
Add to Graph button. Select a second Liquid and click on the Add to Graph
button. Two or more solid/liquid combinations must be chosen in order for points
to be plotted on the graph.
Note: Click on the Add ALL to Graph button to automatically plot each point on
the graph.
Step 5. The surface energies for the given solid are automatically calculated when
two or more solid/liquid combinations have been selected. The error given is
calculated from the Standard Error of the regression in the y-direction.
The Close button closes the window, but keeps the live data.
The Reset button erases the plot and all live data, but does not close the window.
DROPimage Page 47
One Liquid Surface Energy Tool
Purpose
The ‘One Liquid Surface Energy Tool’ evaluates the surface energy of a given
solid using the contact angles of a single test liquid. The surface energy is
calculated from a surface equation of state to describe the correlation between the
contact angle, the surface tension of the liquid, and the surface energy of the solid.
The surface equation of state is
cos   1  2
 S   
e
L
L  S
2
,
where  is an experimentally determined constant. Arguments in the literature
have appeared for using this equation instead of the traditional surface energy or
acid-base methods. The authors referred to determined  = 0.0001247 (mN/m)-2.
The program uses an iterative process to solve this equation for the solid’s surface
energy, L.
Reference: Kwok, D.Y, Neumann, A.W., “Contact angle measurement and
contact angle interpretation”, Adv. Colloid Interface Sci., 81 (1999), 167-249.
Procedure
This is a step by step example of how to use the One Liquid Surface Energy tool:
Step 1. Open the One Liquid Surface Energy tool.
Step 2. Select File|Open from the Tool’s menu and open one or more files
generated by the Contact Angle Tool or from RH Imaging 2001 (denoted by the
DROPimage Page 48
*.CA extension), or use the data already in the Contact Angle Tool. In this
example the PARAFILM.CA file is used. If one or more files are already opened
in the Contact Angle tool, the new records are added to those already present. All
active data are shown in the Contact Angle tool and/or in the Contact Angle File
Control (if open).
Step 3. Select the desired Solid and Liquid from the drop down lists.
Step 4. The surface energy is automatically calculated when the appropriate solid
and liquid combination is selected.
The Close button closes the window, but keeps the live data.
The Reset button erases all live data, but does not close the window.
Take a Picture
By pressing this button, a new image is acquired and displayed in the Main
viewport. The picture may then be measured, copied, saved and filtered.
Filter Picture
The image in the viewport is “filtered”, i.e. the drop’s profile is detected. The
profile may be saved to a binary or text file for later retrieval. In the latter case,
the, data may also be read by other programs, plotted, etc.
Update Plot
The Update Plot button updates the profile plot and cursors in case they have
disappeared, partly or completely, due to windows hiding and un-hiding
operations, in the few cases this is not done automatically.
DROPimage Page 49
APPENDIX
INSTALLATION
To install DROPimage on the hard-disk, please run the DropStdxxxx_Setup.exe
file on the distribution Disk. The installation program also copies the program
icon to your program group of choice. It is recommended that the installation
directory c:\DropImage be used. The Install program will place an icon on your
desktop and a line in the “ramé-hart DROPimage” group in the Start menu.
The program is copy protected, meaning that you will have to obtain a registration
number by calling ramé-hart, instrument co. The registration screen will only
appear the first time you start the program, or by reinstallations. If you reinstall
the program on the same PC, the same registration number may be used.
If you want to uninstall the program and its files, in Windows 2000 or XP, select
the Add/remove programs icon in the Control Panel, select DROPimage Standard
and press Remove. In Windows Vista, select Uninstall a program in the Control
Panel, select DROPimage Standard and select Uninstall from the menu bar. The
Uninstall program does not remove files that have been created after the program
was installed, such as Contact Angle (CA) files, log-files (TXT), Bitmaps (PIC,
BMP, etc.), and Profile file (DAT, TXT). You have to remove these files
manually.