Wetting transitions in a cylindrical pore.

The wetting behavior of two-phase systems confined inside cylindrical pores is studied theoretically. The confined geometry gives rise to wetting configurations, or microstructures, which have no analog in the wellstudied planar case. Many features observed in experiments on binary liquid mixtures in porous media, previously interpreted in terms of random fields, are shown to be consistent with wetting in a confined geometry with no randomness. Disciplines Physical Sciences and Mathematics | Physics Comments At the time of publication, author Douglas J. Durian was affiliated with Exxon Research and Engineering Company. Currently, he is a faculty member at the Physics Department at the University of Pennsylvania. This journal article is available at ScholarlyCommons: https://repository.upenn.edu/physics_papers/635 VOLUME 65, NUMBER 15 PHYSICAL REVIEW LETTERS 8 OCTOBER 1990 Wetting Transitions in a Cylindrical Pore Andrea J. Liu, D. 3. Durian, Eric Herbolzheimer, and S. A. Safran Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801 (Received 26 March 1990) The wetting behavior of two-phase systems confined inside cylindrical pores is studied theoretically. The confined geometry gives rise to wetting configurations, or microstructures, which have no analog in the well-studied planar case. Many features observed in experiments on binary liquid mixtures in porous media, previously interpreted in terms of random fields, are shown to be consistent with wetting in a confined geometry with no randomness. PACS numbers: 64.60.—i, 47.20.Dr, 47.55.Mh, 68.45.6d Binary liquid mixtures inside porous media have attracted considerable attention because of their rich behavior, potential applications, and proposed connection to the random-field Ising model. Experiments on such systems 5 display a variety of results, but two general features consistently emerge: (i) There is metastability and, correspondingly, strong history dependence, deep within the two-phase region; and (ii) macroscopic phase separation does not occur, even far inside the coexistence region of the bulk mixture. Although these features are qualitatively consistent with the random-field model, they are typically observed far from the bulk critical point, where the model is not expected to apply. ' Here, we directly consider the phenomenon of wetting, which plays an important role in porous media. It is notoriously difficult, however, to characterize the contorted geometries of porous media, which, in turn, must influence the wetting behavior. We have ventured away from the well-studied planar case by examining wetting in an idealized geometry, namely, a single cylindrical pore. We have derived a wetting phase diagram and have found that the experimentally observed features, (i) and (ii) above, are qualitatively consistent with our model, which contains no randomness Previous theoretical work on two-phase systems in cylindrical pores has focused on the phenomenon of capillary condensation, where the pore fills up with a single phase rich in the wetting component. A confined geometry in contact with a bulk reservoir at two-phase coexistence will contain only this single, wetting phase. To achieve two-phase coexistence inside a confined geometry, we impose the constraint of constant overall composition (as in experiments on binary liquid mixtures confined in sealed Vycor samples ), and obtain an analog of the wetting transition. Since the constraint requires the system to be finite, the phase transitions we encounter are rounded. A summary of our results for a cylindrical pore of radius ro and length L »ro filled with a binary liquid mixture is given by the wetting phase diagram of Fig. 1. We assume throughout the case of fixed critical composition and symmetric coexistence curve, so that the volume fraction occupied by each phase is 2 . In equilibrium, 8%%%999