Model Calculations for Wetting Studies: The Role of Contact Angle and Adsorption in Wetting Energetics

Abstract

This paper was prepared for the Oilfield Chemistry Symposium of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., May 24–25, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract This distinction between low energy surfaces on which liquids exhibit finite contact angles and high energy surfaces on which liquid spreading occurs is extended to the vapor-solid interface, where it is assumed that multilayer adsorption at saturation pressure of the vapor occurs in the liquid spreading case, while submonolayer adsorption is characteristic of the nonspreading case. An empirical relationship is established between contact angle and adsorption at saturation pressure. Thermodynamic quantities of interest in wetting phenomena are calculated on the basis of energetic parameters in the adsorption expression. Introduction Wetting refers to the interaction between liquid and solid phases in the presence of saturated vapor. Traditionally, the subject has been approached from the observational standpoint (does a liquid drop spread on the subject solid or does it retain a semblance of its drop character?). Interpretation has centered on the mechanical properties of the interfacial systems in analogy to treatments applied to the more accessible liquid-vapor interface. This approach is reflected by the Young Equation, , (1) where terms refer to interfacial tensions, the particular interface being identified by subscripts indicating the phases present and being the angle (measured through the liquid) characterizing the three phase line of contact. Interfacial tensions are recognized as numerically equivalent to interfacial free energies but Eq. 1 remains an expression which reflects but does not quantize the wetting phenomenon since SV and SL are not amenable to measurement. Melrose has cataloged the thermodynamic relationships relevant to the energetics of wetting in a common notational structure and, in so doing, called attention to the energetic parameters which should be accessible to parameters which should be accessible to experiment. These are embodied in the following two equations: (2) (3)