Temperature Dependence of Liquid Contact Angle at a Deformable Solid Surface
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erature Dependence of Liquid Contact Angle at a Deformable Solid Surface A. I. Rusanov* Mendeleev Center, St. Petersburg State University, St. Petersburg, 199034 Russia *e-mail: [email protected] Received April 15, 2020; revised April 20, 2020; accepted April 24, 2020
Abstract—To date, it has been reliably shown by direct methods that a sessile droplet on a solid surface causes deformation of the substrate. For solids with rather low elasticity moduli, in particular, elastomers, this phenomenon becomes observable, and the deformation work reaches values sufficiently large to take it into account in the theory when necessary. Within the framework of the current theory of capillarity and the generalized Young equation, it is most convenient to introduce the deformation work (realized along and inside the three-phase contact line) into the line tension. The resultant effective line tension is several orders of magnitude higher than the usual one (for undeformable solids); therefore, it manifests itself even in macroscopic (although small) droplets. While the usual line tension is just a small correction to the classical Young equation, when elastomers are used as substrates, the effective line tension may become the main term and govern surface phenomena. In this communication, the results of work [Budziak, C.J., Varcha-Butler, E.I., and Neumann, A.W., J. Appl. Polym. Sci., 1991, vol. 42, p. 1959], which is devoted to studying the temperature dependence of liquid contact angles at elastomers, are discussed from the aforementioned points of view. The following facts have been explained: the higher the surface tension of a liquid the larger the contact angle at the same substrate; most probably, the contact angle increases with temperature; the temperature dependence of a contact angle cannot be strong because of the mutual compensation of the temperature dependences of the surface tension of a wetting liquid and the elasticity modulus of an elastomeric substrate. DOI: 10.1134/S1061933X20050142
INTRODUCTION A solid substrate is an inevitable participant of wetting phenomena, with its properties affecting much of the problem in question. Elasticity is an important feature, which distinguish solids from liquids. When studying wetting, the overwhelming majority of solids, whether it be crystalline or amorphous (glassy) bodies, possess high elasticity moduli. In both theoretical considerations and interpretations of experimental data, the use of the model of a perfectly rigid body is a common approach for them. At the same time, there are solids with low elasticity moduli, such as rubbers, vulcanizates, and gels, which are deformable in the course of wetting. The number of such bodies persistently grows due to the development of the chemistry of elastomers and gels. The theory of wetting of deformable solids was substantially developed in the last quarter of the 20th century (see review [1]) due to the discovery of the anisotropic wetting of deformed elastomers. Bartenev and Akopyan [2] were the first to observe this phenom
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