The Dynamics of Solvent Evaporation from Hydroxypropylcellulose/Methanol Solutions with Lyotropic Liquid Crystalline Capability

Thin films of hydroxypropylcellulose (HPC)/methanol (MeOH) solutions were juxtaposed against air in a diffusion couple geometry at room temperature and the solvent was allowed to diffuse away and evaporate from the solution in a controlled manner. The diffusion couple geometry produced a uniform film for optical assessment of liquid crystalline potential between crossed polarizers. After an induction period, a stable microstructure developed in which the interior of the sample remained isotropic followed by a cholesteric liquid crystalline band, with characteristic disclination defects and texture, followed by a crystalline band nearest to the external surface. The width of the total characteristic birefringent band was measured over time and provided information concerning the dynamics and trajectory of solvent transport and evaporation from the cover slip edge. The apparent solvent diffusion coefficient for the HPC/MeOH system was measured at room temperature as a function of initial concentration. Diffusion couple optical microscopy data were compared to both solution rheological characteristics as well as model diffusion data from finite difference calculations in order to validate the observed concentration dependence of diffusion.