Applicaation Repo
ort
Application repo
ort:
AR278
Ind
dustry section
n:
All indu
ustries
Authors:
M. Jin, R.
R Sanedrin, D.
D Frese, C.
Scheithauer, and T. Willers
W
Date:
6
03/2016
Me
ethod:
Keyywords:
Liquid
d Needle as external unit
or inte
egrated in the
e MSA
Drop Shape
e Analyzer –
DSA100
Contactt angle, liquid
d needle, drop
p deposition, super-hydrophobic surfacce
Re
eplacing the solid
d needle by a liqu
uid one when
w
me
easuring
sttatic conttact anglles
Co
omparison of the trad
ditional sollid needle dosing sysstem and a novel preessure-base
ed dosing
system, a so--called Liquid Needle
e
Ab
bstract
Ne
eedle-deposition of sessile
e drops is a well-establishe
w
ed method in
n contact ang
gle analysis. H
However, customers regularly
drops on sup
rep
port user-dep
pendent varia
ations of contact angles aas well as pro
oblems to de
eposit liquid d
per-hydropho
obic
surrfaces, or theyy demand higher deposition speeds. H
Here we prese
ent a new tec
chnique for d
drop deposition that is based
on a Liquid Neeedle in contrasst to a solid one.
o
Further, we highlight the main find
dings of a sciientific study published in the
Jou
urnal of Collo
oid and Polyymer Science (DOI 10.10007/s00396-01
15-3823-1) [1
1] where we thoroughly compared both
b
tecchniques usin
ng 14 differen
nt sample surfaces. We sh
how that the
e resulting co
ontact angles of droplets dosed by eitther
tecchnique are iidentical. In addition, we explain how
w potential pitfalls
p
of nee
edle-dosing – when not carried out very
v
carrefully – are e
eliminated by the alternativ
ve Liquid Neeedle dosing te
echnique.
KRÜ
ÜSS GmbH | Bo
orsteler Chausse
ee 85 | 22453 Hamburg
H
| Germ
many | www.krruss.de
1 | 4
Ba
ackground
Contact angle measurements are wid
dely used ass a
fun
echnique to
ndamental te
o investigate
e and descrribe
surrface and intterface pheno
omena. In multiple
m
fieldss of
ind
dustry such m
measurementss are carried out to optim
mize
adh
hesion of coaatings and understand wetting of liqu
uids
on solid substraates, or as parrt of quality control processses
to check surfacce activation as well as surface
s
clean
ning
ste
eps.
The
e basic way h
how liquid drops are depo
osited onto so
olid
sam
mple surface
es has not changed
c
eve
er since opttical
con
ntact angle measuremen
nts had been
n established
d: A
dro
op of liquid iss generated at
a the tip of a needle, whic h is
ntly
the
en carefully b
brought in co
ontact with an
nd subsequen
transferred to th
he sample surrface.
osing runs in
nto limitation
ns when sup
perThiis way of do
hyd
drophobic su
urfaces or fasst deposition
n speeds are an
issu
ue [1]. In add
dition, errone
eous results may
m be obtain
ned
if the
t
drop dep
position is not performed
d very carefu
ully.
Variations in me
easured conttact angles be
etween differrent
use
ers can occurr (see Fig. 1), while it is of high interestt to
ren
nder the expe
eriment as use
er-independe
ent as possiblee.
Fig
g. 2: Formation
n/deposition o
of a drop of water
w
on a PD
DMS
surrface. Left: cla
assical needlee dosing syste
em (NDS). Right:
new
w pressure-based Liquid Needle dosin
ng system (PDS).
Fig
gure from reference [1] with kind permissiion of Springe
er.
In order to show
w that the neew technique
e leads to results
equal to those obtained
o
withh (thoroughly
y applied) nee
edle
do
osing, we hav
ve performed
d an extensive comparative
stu
udy between both dosing ttechniques.
Ex
xperimental section
Sta
atic contact angle
a
measureements were performed with
w
a Drop
D
Shape Analyzer – D
DSA100 and evaluated ussing
the
e software AD
DVANCE. To aassure a repeatable and usserind
dependent drop depositio
on, an autom
matic proced
dure
wa
as defined in the
t software ffor both dosing systems.
Eacch different sample
s
was aanalyzed with
h the same liight
setttings and fitting
f
algorrithms. Meassurements were
w
carrried out under ambient co
onditions.
Co
ontact angle measurement
m
ts were carried out on 14 very
v
diffferent sample
es:
 Hydrophilic
H
su
urfaces (glasss, smartphone
e display)
Fig. 1: Deposition
n of a drop off water onto a PDMS substrrate.
Eve
en small chang
ges in needle position can cause
c
the drop
p to
be squeezed an
nd thus lead to different (smaller) conttact
ang
gles. This efffect is particularly important for surfaaces
exh
hibiting large ccontact angle hysteresis.
To avoid these potential pitffalls, we have
e developed aand
implemented an alternatiive pressure
e-based dossing
tecchnique whicch builds the
e drop with a well-defin
ned
liqu
uid jet (referrred to as Liq
quid Needle) directly on the
sub
bstrate (see FFig. 2). The Liquid Needle is optimized
d to
deposit a drop
p as carefully as possib
ble, while otther
nee
edle-less tech
hniques repo
orted in literatture introducce a
con
nsiderable am
mount of kin
netic energy into the drrop,
cau
using the dro
op to “splash
h” onto the surface. Conttact
ang
gles obtaine
ed from e. g. falling drops
d
thereffore
desscribe the ressult of a de-w
wetting proce
ess and are m
most
oftten significan
ntly smaller th
han contact angles obtain
ned
fro
om needle dosing systems..
 Hydrophobic
H
surfaces (P22i super-hydrophobic paper,
polydimethyls
p
siloxane PDM
MS)
 Technical
T
poly
ymers (polyetthylene PE, po
olypropylene PP,
polyamide
p
PA
A6)
 Silicon
S
waferss (wafer 1, waffer 2)
 Self-assemble
S
ed monolayyers on SiO
S 2 (dichlo
orodimethylsilane
d
e DDMS, aminopropyltrimethoxysilane
APTMS)
A
 Rough
R
surfaces (DDMS-sillanized sand papers of grain
sizes
s
500, 100
00, and 1500)
With the samp
ples we coverred a broad range of wa
ater
contact angles from very l ow (smartph
hone display)) to
verry high (P2i hydrophobicc paper) and
d also differrent
degrees of surrface homog
geneity (from
m homogeneous
SA
AMs to sand paper
p
samplees with a maccroscopic surfface
rou
ughness).
All samples were
w
cleaned
d and dried
d prior to the
me
easurements. A detai led descrip
ption of the
exp
perimental se
etup and thee sample preparation can be
fou
und in the cite
ed reference [1].
KRÜ
ÜSS GmbH | Bo
orsteler Chausse
ee 85 | 22453 Hamburg
H
| Germ
many | www.krruss.de
2 | 4
Re
esults
The
e results of contact ang
gle measurem
ments on thee 14 samples are shown
n in Fig. 3a aand Fig. 3b, with water and
a
diio
odomethane as test liquids, respectively.
a
b
domethane (bo
ottom, 3b) contact angle ass measured aft
fter dosing witth the NDS (open
Fig. 3: Mean stattic water (top, 3a) and diiod
columns) and PD
DS (filled colu
umns). The errror bars reflecct the standarrd deviation as obtained fro
om a minimum of 20 differrent
ops measured.. Figures adap
pted from reference [1] with kind permissiion of Springer.
dro
Forr all sampless, both ways of dosing give
g
comparaable
con
ntact angles aand small standard deviations.
Concerning the
e effect of th
he needle de
eposition on the
con
ntact angle on surfaces with a high
h contact an
ngle
hyssteresis such as PDMS (see fig. 1), on
ne can conclu
ude
tha
at the liquid needle is an
n even more
e careful wayy of
dro
op deposition
n than the solid needle, as the resultting
con
ntact angle o
on PDMS is evven higher for PDS compaared
to NDS [1].
ond, non-polar test liquid we
Forr diiodomethane as a seco
also obtained w
well-compara
able contact angles for b
both
dosing types (FFig. 3b). For glass, the co
ontact angless of
1 µL
han
µ drops dose
ed by PDS were
w
significan
ntly smaller th
tho
ose dosed by NDS. This ca
an be explaine
ed by the hig
gher
density of diio
odomethane compared to
t water, wh
hich
brings more kin
netic energy into the dro
op [1]. A sim
mple
way to rule ou
ut the influen
nce of this ad
dditional kineetic
energy on con
ntact angles is to dose a recommend
ded
dro
op volume of
o 2 to 2.5 µµL instead off 1 µL. Then the
kin
netic energy of the liquid
d jet dissipate
es over a larrger
dro
op volume and
a
both do
osing systemss yield identtical
contact angles (dark
(
blue co lumns).
n super-hydro
ophobic surfaaces like the P2i paper, it was
w
On
not possible to transfer drop
ps of volumess as small as 3 µL
to the surface with
w the NDSS. This is due to the very low
surrface free en
nergy (very lo
ow adhesive interactions)) of
this sample. Therefore drop s of 6 µL had
d to be used for
ND
DS (Fig. 3a, green
g
bar). Inn contrast, drops of virtu
ually
anyy volume can
n be dosed onn such samples with the PDS.
P
This is somethin
ng we consideer a strong po
oint of the PD
DS.
matic measureement of 20 drops using the
The fully autom
ND
DS and the PDS
P
usually ttook around 220 s and 54
5 s,
resspectively, which
w
makess the PDS a much faster
tecchnique for an
nalyzing a surrface.
KRÜ
ÜSS GmbH | Bo
orsteler Chausse
ee 85 | 22453 Hamburg
H
| Germ
many | www.krruss.de
3 | 4
Summary
We present a new way of dosing called Liquid Needle
which is based on a liquid jet building up a drop on a
solid substrate for static optical contact angle
measurements. This new technique is compared with the
classical technique of using a solid needle for dosing in a
study of two common test liquids on 14 very different
solid substrates.
The obtained contact angles are basically identical for
both drop deposition methods, while the Liquid Needle
method offers some advantages over the classical
method: experiments are much faster and drop
deposition on super-hydrophobic surfaces is easily
possible.
Most importantly, any possible influence by the user and
resulting issues with reproducibility of results are virtually
ruled out for this novel drop deposition technique. This
will help to further increase the comparability of contact
angles measured by various groups. In conclusion, we
believe that using the Liquid Needle is advantageous for
many contact angle studies and may become another
standard method in optical contact angle measurements.
A detailed description of all experimental conditions and
discussion of all results can be found in the article
published in the Journal of Colloid and Polymer Science
[1].
Literature
[1]
M. Jin, R. Sanedrin, D. Frese, C. Scheithauer and T.
Willers, “Replacing the solid needle by a liquid one
when measuring static and advancing contact
angles”, Colloid Polym. Sci. 294(4), 657-665,
DOI 10.1007/s00396-015-3823-1 (2016).
KRÜSS GmbH | Borsteler Chaussee 85 | 22453 Hamburg | Germany | www.kruss.de
4 | 4