Apparent and Microscopic Contact Angles

472 Pages·2000·25.25 MB·English

by  Drelich

APPARENT
AND
MICROSCOPIC
CONTACATN GLES
Editors:
J Dreich, JS. Laskowski
af7dK:L. Miffs/
vs
/// P///
Utrecht Boston Koln Tokyo
2000
VSP BV Tel: [phone]
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0V SP BV 2000
First published in 2000
ISBN 90-6764-32 1-1
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permission of the copyright owner.
Printed in The Netherlands by Ridderprint bv, Ridderkerk.
Apparent and Microscopic Contact Angles, pp. ix-x
J. Drelich, J. S. Laskowski and K. L. Mittal (Eds)
0 VSP 2000.
Preface
This book chronicles the proceedings of the International Symposium on Apparent
and Microscopic Contact Angles held in conjunction with the American Chemical
Society Meeting in Boston, August 24-27, 1998.
The symposium was truly international and interdisciplinary and provided a forum
for almost 100 chemists, metallurgists, physicists and biologists from 17 countries
(Australia, Belarus, Belgium, Brazil, Canada, France, Germany, Israel, Italy, Japan,
Poland, Russia, Singapore, Sweden, Turkey, the United Kingdom and the United
States). The program included almost 70 oral and poster presentations.
The symposium in Boston provided an opportunity to discuss several controver-
sial issues associated with interfacial phenomena that govern the behavior of the
three-phase systems. Particularly welcomed were contributions on the molecular
and nanoscopic effects in wetting phenomena. We are on the verge of understanding
the arrangements of molecules at interfaces and their effect on microscopic proper-
ties of the three-phase systems, such as interfacial forces, interfacial tension, linear
excess energy, etc. The interfacial transition regions between immiscible phases are
the subject of current experimental and theoretical investigations, and the progress
in imaging and understanding of these regions was reported in Boston. Signifi-
cant improvements in examination of the line tension values were demonstrated,
although it is still uncertain whether the linear excess energy is of any importance
in practical situations.
It is well recognized in our scientific community that among the most significant
topics are the ones concerning the determination of the surface free energy of
solids through contact angle measurements. The models developed to determine
the surface free energy of solids from contact angle measurements, as pointed out
at the forum, still require improvements.
The methodologies and interpretations of the contact angle measurements at
heterogeneous, rough and/or powdered solids are vital in the area of applied surface
chemistry, and the number of papers presented at the symposium proves this point
very well. Although the material presented was ‘state-of-the-art’, both modeling
and experimentation with heterogeneous and rough surfaces are in an early stage
development, and we hope that this symposium stimulated the progress in this area.
The lecture room in which sessions of the International Symposium on Apparent
and Microscopic Contact Angles were held was overcrowded up to the very last
x Preface
presentation. This is another indication that advances in understanding of the
wetting phenomena attract the attention of a very broad audience.
As for this book, it contains 28 papers which were earlier published in three issues
of the Journal ofAdhesion Science and Technology (JAST) as follows: Volume 13,
No. 10 and No. 12, and Volume 14, No. 2. However, a large number of people
indicated interest in acquiring these three issues separately; concomitantly, we
decided to bring out this hard-bound book. It should be noted that in the book the
papers have been rearranged in a more logical manner vis-8-vis the order in which
they were published in the special issues of JAST.
The book is divided into four parts as follows: Part 1. Nanoscopic and Molecular
Effects on Contact Angles; Part 2. Surface Forces and Surface Free Energy; Part 3.
Wetting of Heterogeneous, Rough and Curved Surfaces; and Part 4. Dynamic
Effects in Contact Angle Measurements. The topics covered include: contact line
tension measurement; liquid drop surface topography; molecular mechanism of
hydrophobic transitions; stereochemical and conformational aspects of polymer
surfaces; determination of acid- base properties of metal oxides and polymers
by contact angle measurements; van Oss-Good theory of acid-base surface
free energies; AFM measurement of forces; thin liquid films; wettability of flat
and curved surfaces; contact angle hysteresis; factors affecting contact angle
measurements; dynamic wetting behavior; and effect of surfactants on wetting.
Now comes the pleasant task of thanking those who contributed in many and
varied ways. First, we would like to thank the session chairpersons: Terry D. Blake,
Ana M. Carmona-Ribeiro, Jaroslaw Drelich, Robert J. Good, Karina Grundke,
Robert Hayes, Janusz S. Laskowski, Lieng-Huang Lee, Glen McHale, John Ralston
and Claudio Della Volpe, for doing an excellent job in moderating the sessions.
The authors should be thanked for their contribution, cooperation, interest and
enthusiasm. The time and efforts of the reviewers in providing valuable comments
is gratefully acknowledged. We would like to acknowledge the assistance of the
American Chemical Society through the Petroleum Research Fund Program and
Division of Colloid and Surface Chemistry; University of Utah through the College
of Mines and Earth Sciences; Michigan Technological University through the
Department of Metallurgical and Materials Engineering; and University of British
Columbia through the Department of Mining and Mineral Process Engineering, for
support of the symposium. Last, but not least, we are appreciative of the excellent
job done by the VSP staff in producing this book.
We sincerely hope this book summarizing the cumulative wisdom of a legion
of researchers and commenting on the contemporary research will serve as a
fountainhead for new ideas in the wonderful (but complex) world of contact angles.
Jaroslaw Drelich
Janusz S. Laskowski
K. L. Mittal
Contents
Preface ix
PART 1. NANOSCOPIC AND MOLECULAR EFFECTS ON
CONTACT ANGLES
Measurement of contact line tension by analysis of the three-phase
boundary with nanometer resolution
is Pompe, A. Fery and S. Herminghaus 3
Nanometer resolution of liquid surface topography by scanning force
microscopy
A. Fery, is Pompe and S. Herminghaus 13
Instability of the three-phase contact region and its effect on contact
angle relaxation
J. Drelich 27
Molecular mechanisms of hydrophobic transitions
V V Yaminsb 47
Wetting of SiO2 surfaces by phospholipid dispersions
L. C. Salay and A. M. Carmona-Ribeiro 95
Wettability and microstructure of polymer surfaces: stereochemical and
conformational aspects
0. N. Tretinnikov 111
Contact angles on quartz induced by adsorption of heteropolar
hydrocarbons
X. Xie and N. R. Morrow 129
PART 2. SURFACE FORCES AND SURFACE FREE ENERGY
Determination of the acid-base properties of metal oxide films and of
polymers by contact angle measurements
E. McCafferty and J. P. Wightman 149
Acid-base surface free energies of solids and the definition of scales in
the Good-van Oss-Chaudhury theory
C. Della Volpe and S. Siboni 171
vi Contents
The gap between the measured and calculated liquid- liquid interfacial
tensions derived from contact angles
L.-H. Lee 209
Effect of an external radiofrequency electric field on the surface free
energy components of calcium carbonate in the presence of cationic and
anionic surfactants
E. Chibowski, L. Hotysz and M. Lubomska 229
AFM measurements of hydrophobic forces between a polyethylene
sphere and silanated silica plates - the significance of surface roughness
J. Nalaskowski, S. Veeramasuneni, J. Hupka and J. D. Miller 245
Self-organization in unstable thin liquid films: dynamics and patterns in
systems displaying a secondary minimum
J. Singh and A. Sharma 26 1
PART 3. WETTING OF HETEROGENEOUS, ROUGH AND
CURVED SURFACES
Underwater captive bubble technique on curved surfaces of blended
poly dimethylsiloxanes
E. A. Angu, R. C. Cameron, S. K. Pollack and W E. Collins 285
Thermodynamic equilibrium and stability of liquid films and droplets on
fibers
A. I? Neimark 301
Estimation of contact angles on fibers
G. McHale, S. M. Rowan, M. I. Newton and N. A. Kab 3 19
Evolution of surface chemistry and physical properties during thin film
polymerization of thermotropic liquid crystalline polymers
K. -X. Ma, T. -S. Chung, P: K. Pallathadka and S. -S. Feng 333
The combined effect of roughness and heterogeneity on contact angles:
the case of polymer coating for stone protection
C. Della Volpe, A. Penati, R. Peruzzi, S. Siboni, L. Toniolo
and C. Colombo 349
Microsphere tensiometry to measure advancing and receding contact
angles on individual particles
S. Ecke, M. Preuss and H.-J. Butt 377
Wettability of fine solids extracted from bitumen froth
F: Chen, J. A. Finch, Z. Xu and J. Czarnecki 389
Modification of calcium carbonate surface properties: macroscopic and
microscopic investigations
M. Chamerois, M. Francois, F: Villie'ras and J. Yvon 405
Contents vii
Factors influencing contact angle measurements on wood particles by
column wicking
M. E. P. Wiilinder and D. J. Gardner 419
A new model to determine contact angles on swelling polymer particles
by the column wicking method
S. Q. Shi and D. J. Gardner 43 1
PART 4. DYNAMIC EFFECTS IN CONTACT ANGLE
MEASUREMENT
Determination of the peripheral contact angle of sessile drops on solids
from the rate of evaporation
H. Y Erbil 447
Analysis of evaporating droplets using ellipsoidal cap geometry
H. I: Erbil, G. McHale, S. M. Rowan and M. I. Newton 457
Surfactant-induced wetting singularities in confined solid- liquid-liquid
systems: kinetic and dynamic aspects
H. Haidara, L. Vonna and J. Schultz 475
An acoustic technique for the monitoring of dynamic wetting behavior
G. McHale, M. I. Newton, M. K. Banerjee and S. M. Rowan 487
Dynamic contact angle explanation of flow rate-dependent
saturation- pressure relationships during transient liquid flow in
unsaturated porous media
S. l? Friedman 497
Subject index 521
Author index 523
Part 1
Nanoscopic and Molecular
Effects on Contact Angles
Apparent and Microscopic Contact Angles, pp. 3- 12
J. Drelich, J. S. Laskowski and K. L. Mittal (Eds)
0 VSP 2000.
Measurement of contact line tension by analysis of the
three-phase boundary with nanometer resolution
T. POMPE, A. FERY and S. HERMINGHAUS 2,*
'
MPl fur Kolloide und Grengachen, 0-14424 Potsdam, Germany
Abteilung Angewandte Physik, Universitat Ulm, Albert-Einstein-Allee 1I , 0-89081, Ulm, Germany
Received in final form 11 February 1999
Abstract-Liquid structures on solid substrates have been imaged with a resolution in the nanometer
range by scanning force microscopy in the tapping mode. Using substrates with an artificially
patterned wettability, characteristic features in the three-phase contact line were induced, which allow
the contact line tension to be determined. The values in the range of -1 x N obtained for
sessile droplets of hexaethylene glycol are consistent with theoretical predictions.
Key words: Contact line tension; scanning force microscopy; modified Young equation.
1. INTRODUCTION
The contact line tension, i.e. the excess free energy of a three-phase contact line, is
probably the most controversial quantity in wetting science. This is mainly due
to its poor accessibility. The theory predicts that typical values of the contact
line tension, t,s hould be in the range of a few tens of piconewtons [ 1-71, The
characteristic length scale, I, at which these forces become important can readily
be obtained by comparison with typical values of interfacial tensions, y, yielding
1 := t / y x lo-" N/10-2 N m-l -- 1 nm. At much larger scales, interfacial
tensions are expected to dominate all measurements of line tension effects, and
particular care must be taken in experiments. The classical approach for tackling
the problem is to investigate the dependence of the contact angle of small sessile
droplets on their size. The smaller a droplet becomes, the larger the effect of the
contact line tension on its shape. For a positive line tension, the droplet base is
contracted, which gives rise to a larger value of the contact angle. This is expressed
by the modified Young equation for a liquid droplet on a plane solid surface, which
*To whom correspondence should be addressed. E-mail: [email protected]
4 7: Pompe et al.
reads
1 ,
cos(@) = cos(@yo",g) - -1 -1
Y R'
where 0 is the actual contact angle that the droplet forms with the substrate and
is the contact angle which would be derived from Young's equation (Le. for
@young
a straight contact line or an infinitely large drop). R is the radius of the (circular)
contact line and y is the surface tension of the liquid. This nomenclature will be
used throughout this paper. Assuming the theoretically predicted values of the
contact line tension to be true, one is faced with the necessity of investigating
extremely small droplets in order for the change in contact angle to be measurable.
For instance, for a water droplet, a radius of contact line curvature of 20 nm on a
substrate with Young's contact angle of 30" gives rise to a change in the contact
angle (with respect to its value for a straight contact line) of only 1" when a contact
line tension of lo-" N is assumed. In marked contrast, experiments have been
performed for a long time using optical techniques on droplets with typical sizes of
at least several tens of micrometers. The results show an exceptionally large scatter
in the magnitude of the contact line tensions obtained: values ranging from lop5t o
N, both positive and negative, are reported in the literature [8-121.
From the diagram presented in Fig. 1, it is quite straightforward to imagine how
such a large scatter in the experimental values of the contact line tension may
come about. Since every surface is, as far as its surface energy is concerned,
inhomogeneous at least at a very small scale, the contact line is expected to
exhibit a corrugation as shown in the figure, which is not accessible with optical
imaging techniques. As a consequence, the total free energy of the contact line
which is measured using a coarse-graining experimental technique (such as optical
microscopy) consists not only of the genuine contact line tension or its sum over the
corrugations as proposed by Neumann and co-workers [13], but also of the excess
free energy connected to the increased total surface near this line. Since the typical
length scale at which the wettability of the substrate varies is likely to exceed the
above-mentioned critical length 1, the measured line tension may well exceed its
Figure 1. Schematic diagram of a macroscopic liquid droplet on a microscopically heterogeneous
surface. Optical techniques would yield an apparent radius of curvature of the contact line from the
base of the macroscopic droplet. The real radius of curvature of the contact line (from the local
corrugations) is beyond their resolution limit.