"STUDY OF SELF-ORGANIZATION OF SILVER HALIDES IN GEL-LIKE
PHASES IN THE PRESENCE OF CONVECTION"
A. MINAŘÍK, L. Lapčík, L. Lapčík, jr.
Tomas Bata University in Zlin, Institute of Physics & Material Engineering,
Nad Stráněmi 4511, CZ – 760 05 Zlín, Czech Republic
e-mail: [email protected], web: www.ft.utb.cz/czech/UFMI
Phone: +420 57 603 5086 Fax: +402 57 603 5141
KEY WORDS
self-organization, Bénard-Marangoni convection, silver halides, gel-like phases, polysaccharides
Introduction
Study of self-organization is very interesting from the
theoretical point of view with respect to understanding the basic physical phenomena and the
mutual bonds of these complex structures creation.
This problem is also interesting from the practical
point of view. Advantageous results may be
received connected with practical application of thin
polymer layers on different surfaces. For-example in
applied surface protection layer containing minimal
amount of defects and differently organized
functional microstructures, with an application
in industrial area and medicine.
What is self-organization? It is a process, which is
working “alone” without any external driven forces influence (“without manager”), resulting in a creation
of organized structures and patterns by means
of mutual interaction of units on the same level. This
process is very sensitive to initial conditions and it is
connected with transport of matter and energy, nonlinearity, non-reversibility and stochasticity. For
purposes of our research Bénard-Marangoni
convection was chosen as a model, with regard
to the extensive study of this problem in last years
[1-3]. This instability is characteristic for liquid with
a free surface and it is thickness smaller than 1 cm.
The dominant effect seem to be change in surface
tension, as a result of temperature fluctuation in the
surface layer.
As a dispersion medium for inorganic particles,
aqueous solution of hydroxyethyl cellulose was used,
with respect to it is ability to create hydro-gels with
certain amount of bonded water and a tendency to
self-aggregation during the solvent evaporation.
The main aim of this study was evaluation of the
factors determining a creation and a fixation of the
organized structures (Bénard-Marangoni cells
and crystals AgBr, AgCl, etc.) in gel-like matrix
of hydroxyethyl cellulose. This problem has not been
properly studied and explained for the complicate
character of the solidification process under
presence of dispersed silver halides [1,3,4].
Experimental
Materials and methods:
Hydroxyethyl cellulose (2-HEC), silver nitrate
(AgNO3), lithium bromide (LiBr) was obtained from
Sigma-Aldrich in p.a. quality. The molecular weight
4
of 2-HEC was 9×10 Da.
Concentration of 2-HEC in solution was 1g in 100 g
of de-ionized water, viscosity of the prepared 2-HEC
in water was around 3 mPa.s. Dispersion of AgBr
was prepared by precipitation reaction stated in
Figure 2. First silver nitrate and lithium bromide were
separately dissolved in water. After dissolution were
these solutions mixed with concentrated 2-HEC
in water.
Substrates for preparation of thin layer films from
solution were glass Petri dishes, carefully cleaned
with chromsulfuric acid, ethanol and de-ionized
water by usual procedure.
The thin polymer films were prepared in special
Micro-condensation drying system – MCDS, which
has been developed for the purposes of this study.
The whole MCDS consist of 8 sub-units situated on
two special anti-vibration tables and regulated with
four independent sub-systems.
The created self-organized structures, in the range
of this paper, were characterized by means of the
optical microscopy. Optical microscope Nikon,
Eclipse E50i and digital camera Canon Power Shot
A640 with resolution 10 Mpix, were used.
Results and discussion
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Fig. 1. Examples of organized structures of 0,01 M AgBr
(starting concentration) in hydroxyethyl cellulose films
prepared at different conditions: A) T = 0,3 °C, velocity
of drying = k; B)T = 6 °C, velocity of drying = 1,3k.
Figures were obtained from optical microscopy (image
in behind represents edge of circle film).
Conclusions
Based on the experimental results it can be
concluded: self-organization of silver halides (AgBr,
AgCl, etc.) in gel-like phases of hydroxyethyl
cellulose is a complex process, depending on
concentration and types of reagents, dispersive
medium, temperature, temperature gradient, velocity
of drying, etc. These very sensitive processes result
in creation of characteristic structures (BénardMarangoni cells) with different distribution of
crystallic and polymeric material in the studied films,
which is evident in Figures 1 and 2.
Acknowledgements
The authors would like to express their gratitude for
financing of this research by the Ministry
of Education, Youth and Physical Training of the
Czech Republic (Grant VZ MSM7088352101).
AgNO3 + LiBr  AgBr + LiNO3
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Fig. 2. Examples of organized structures of 0,05 M AgBr
(starting concentration) in hydroxyethyl cellulose films
prepared at different conditions: A) T = 0,3 °C, velocity
of drying = k; B)T = 6 °C, velocity of drying = 1,3k.
Figures were obtained from optical microscopy (image
in behind represents edge of circle film).
References
[1] Coline, P., Legros, J. C. Valerde, M. G. Nonlinear
Dynamics of Surface-Tension-Driven Instabilites.
Wiley-VCH Berlin, 2001. ISBN 3-527-40291-8
[2] Sakurai, Sh., Furukawa, Ch., Okutsu, A., Miyoshi,
A. Nomura, Sh. Control mesh pattern of surface
corrugation via rate of solvent evaporation in
solution casting of polymer film in the presence
of convection. Polymer. 2002, vol. 43.
[3] Schatz, M. F., Vanhook, S. J., Mccormick, W. D.,
Swift, J. B., Swinney, H. L. Time-independent
square patterns in surface-tension-driven Bénard
convection. Phys.Fluids. 1999, vol. 11, p. 2577-2582.
(taken from Colinet - 2001).
[4] Sperka, G. Crystal growth in gels – a survey.
Progress in Colloid & Polymer Science. 1988,
vol. 77.