RELATION BETWIGEN e @ N T A C T ANGLE AND SURFACE ROUGHNESS ceramic surfaces by the variable-temperature method, it is safe to say that the analysis of contact angle behavior as a function of solid surface composition and liquid surface tension is now essentially consistent for a large variety of surfaces over a wide range of e have shown the similarity of the temperature effect on yo for a variety of low-energy surfaces. As yet this cannot be done for high-energy
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surfaces because the results are not couched in a language which we can presently handle. The concepts of yo, -yes,and T,,, and the recognition that ye is essentially a function of surface composition and a linear decreasing function of temperature appear adequate to provide a sound foundation and a framework on which to broaden the whole field concerned with the contact angle, spreading, and wetting.
Experimental Study of the Relation between Contact Angle and Surface Roughness by Y. Tamai and K. Aratani*l Chemical Research Institute of Nan-Aqueous Solutions, Tohoku University, Sendai, J a p a n
(Receized November 15, 1071)
Publication costs assisted by the Research Laboratories of Kawasaki Steel Corporation
The effect of surface roughness on the contact angle of a liquid was studied for the silica glass-mercury system using the sessile drop method. Silica glass plates were roughened in three different ways and classified in three groups. Considering the roughness profiles and the electron micrographs of these surfaces, a model of roughened surface was proposed. Assuming Wenzel’s relation, the parameters of the model were estimated from the experimental data of one group. The experimental data of the other two groups were explained satisfactorily by this model, proving Wenzel’s theory t o hold.
Introduction It is a well-known fact that the contact angle of a
measured with a sessile drop of mercury on the surface of silica glass which was roughened to various extents.
sessile liquid drop on a plane surface of a solid depends Experimental Section largely on thc roughness of the plane. To explain the Preparation of the Specimen. The silica glass plates effect of roughness, Wenze12proposed a theory in which used were of 10 X 10 X 1 mm in size and roughened in the increase in the surface area of a roughened plane is three different ways. The first way was t o abrade the shown to be responsible for the change of the contact specimen with carborundum abrasive followed by sucangle. After Wenzel, Gassie and B a ~ t e r D , ~e r ~ a g i n , ~ cessive polishings for different times with diamond Shuttleworth and Bailey,6 Good,6 and Johnson and paste. In this way the prepared specimens had Dettre’ have tried to derive Wenzel’s relation by thermodifferent surface finishes ranging from a maximum dynamic treatments. Several investigators have compared the experimental results with Wenzel’s equa(1) Research Laboratories of Kawasaki Steel Corp., Chiba, Japan. tion. However some of the comparisons %-ereof qual(2) R. N. Wenzel, I n d . Eng. Chem., 28, 988 (1936). itative natureJ8and others were not successful in com(3) A. B. D. Cassie and S. Baxter, Trans. Faraday Sac., 40, 546 (1944). paring the results with the theoryeg (4) €3. V. Deryagin, Dokl. Akad. Nauk U S S R , 51, 357 (1946). The present work was planned to examine the rela(5) R. Shuttleworth and G. L. J. Bailey, D ~ C U SFaraday S. SOC.,3, tion between the measured contact angle and the rough16 (1948). ness of a surface on the basis of Wenzel’s equation, by (6) R . J. Good, J. Amer. Chem. Soc., 74, 5041 (1952). making an approximate model of surface geometry (7) R. E. Johnson, Jr., and R. Dettre, Surface Colloid Sci., 2, 85 (1969). consistent with experimental observation and by intro(8) R. E. Johnson and R. H. Dettre, Advan. Chem. Ser., No. 43, 112 ducing the roughness factor based on this model into (1963). Wenzel’s equation. (9) F. E. Bartell and J. W. Shepard, J . Phvs. Chem., 57, 211, 455, For this purpose the advancing contact angle was 458 (1953). The Journal of Physical Chemistry, Val. 76, S o . $9,197.9
Y. TAMAI AND I
