Crossover in the wetting behavior at surfactant-laden liquid-crystal–water interfaces: Experiment and theory

Abstract

The behavior of a nematic liquid crystal at a surfactant-laden interface to an aqueous phase is studied under the condition of homeotropic anchoring. It is shown that with decreasing surfactant concentration the system shifts from surface-enhanced to surface-decreased order, i.e., the behavior changes from complete nematic wetting when the nematic-isotropic phase transition is approached from above to a different wetting behavior below the transition, characterized by a considerably decreased Maier-Saupe order parameter at the interface. The experimental behavior is analyzed within the framework of the Landau-de Gennes theory supplemented by a surface free energy, in which the wetting behavior is controlled by the magnitude of the anchoring strength and the preferred surface order parameter in comparison to the bulk order parameter. The theoretical modeling is able to account for all experimental observations.

Effects of surface anchoring on the electric Frederiks transition in ferronematic systems

“…5 area 1 is larger than area 2 and by the way the first cross point provides absolute minimum at the total free energy. This condition is well-known as the Maxwell construction [33,34]. The NLC director selects x 1 as the only acceptable value of θ 0 at the boundary surfaces.…”

Scattering of Light on Surfactant-Laden Liquid-Liquid Crystal Interface

“…The surfactant film at the nematic-isotropic interface reduces surface tension (Kim et al, 2004) and induces anchoring of the nematic liquid (Brake and Abbott, 2002;Brake et al, 2003;Kadivar et al, 2007). The presence of the adjacent nematic phase results in the anisotropy of the surface viscoelastic coefficients (Rey, 2000).…”

“…Surfactant-laden liquid-liquid crystal interfaces demonstrate interesting phase behavior (Price and Schwartz, 2007;Gupta et al, 2008), anchoring (Brake and Abbott, 2002;Brake et al, 2003;Kadivar et al, 2007), and wetting (Bahr, 2006) properties. Surfactants play an important role in the formation and stability of liquid-crystal emulsions (Kim et al, 1998;Park and Lee, 1999;Yamamoto and Tanaka, 2001;Caggioni et al, 2005).…”

Surface order at surfactant-laden interfaces between isotropic liquid crystals and liquid phases with different polarity

“…LCaqueous interfaces provide the advantage that the surfactant coverage of the interface can easily be varied by changing the surfactant bulk concentration. The resulting well-defined control of the ordering surface field enabled the study of novel wetting behaviors [34], smectic layering transitions [35], and nematic prewetting transitions [36].…”

“…In the above-mentioned studies [21,[34][35][36], we investigated the interface between LCs and either pure water or water doped with a small amount of surfactant (ionic surfactants were dissolved in the aqueous phase, nonionic surfactants in the LC bulk phase). In practice, liquid phases constituting emulsions are often multicomponent systems in which water is just one of several components.…”