Capillary Thermodynamics of Nematic Polymer Interfaces

The Cahn‐Hoffman capillarity vector thermodynamics formalism for curved anisotropic interfaces is adapted to soft liquid crystalline polymer‐isotropic fluid interfaces. The Cahn‐Hoffman formalism in conjunction with the interfacial Landau‐de Gennes model is used to derive compact expressions for the capillary pressure, tangential Marangoni force, and interfacial torque. It is shown that the interfacial thermodynamics of nematic polymers can be analyzed in terms of three distinct modes: (i) area size change, (ii) area rotation, and (iii) tensor order parameter curvature. The formalism allows to clearly identify the nature and magnitude of these three contributions. Characteristic cases biaxial and uniaxial nematic ordering states are analyzed. Anisotropic liquid crystal surfaces display a number of novel interfacial effects: (a) capillary pressure even for flat surfaces, (b) tensor order parameter‐dependent renormalization of the tension coefficients due to anchoring energy, (c) tensor order parameter‐driven transitions between classical Laplace pressure and non‐classical behavior, (d) Laplace‐like capillary pressure due solely to orientation curvature, (e) generation of Marangoni forces through interfacial order and/or orientation gradients, and (f) surface torques generation.

Schematic of the geometry considered in this article.