Shear Rheology of Lyotropic Liquid Crystals

摘要

We report on the rhological signatures of lyotropic liquid crystals (LC) formed by self-assembled lipids and water, and their dependence on phase structure, temperature and water content. Rheology in the linear viscoelastic regime revealed a specific signature that was characteristic of the topology of each liquid crystalline phase. Lamellar-to-cubic and cubic-to-hexagonal transitions, as well as transitions from each LC to isotropic fluid were easily identified by following the development of the storage and loss moduli, G' and G", respectively. Viscoelastic properties of both Ia3d and Pn3m cubic phases were shown to be strongly frequencydependent, following a pseudo-Maxwell behavior, with multiple relaxation times. Cubic-to-cubic transitions were captured by scaling the longest relaxation time, τ, with temperature and water volume fraction. Therefore, the set of the G', G'' and relaxation time τ, constitutes a consistent ensemble to identify the structure of the liquid crystal. Similar conclusions could be drawn by comparing relaxation spectra, for all liquid crystalline phases.