Structural Rheology of the Smectic Phase

Effects of shear-induced crystallization on the complex viscosity of lamellar-structured concentrated surfactant solutions

Material relationships at low temperatures were determined for concentrated surfactant solutions using a combination of rheological experiments, cross-polarized microscopy, calorimetry, and small angle X-ray scattering. A lamellar structured 70 wt% solution of sodium laureth sulfate in water was used as a model system. At cold temperatures (5 °C and 10 °C), the formation of surfactant crystals resulted in extremely high viscosity. The bulk flow behavior of multi-lamellar vesicles (20 °C) and focal conic defects (90 °C) in the lamellar phase was similar. Shear-induced crystallization at temperatures higher than the equilibrium crystallization temperature range resulted in an unusual complex viscosity peak. The effects of processing-relevant parameters including temperature, cooling time, and applied shear were investigated. Knowledge of key low-temperature structure-property-processing relationships for concentrated feedstocks is essential for the sustainable design and manufacturing of surfactant-based consumer products for applications such as cold-water laundry.

Energy dissipation mechanism of annihilating reverse tilt domains for various applied voltages

When a voltage is applied to a uniformly aligned nematic liquid crystal, a characteristic texture designated as reverse tilt domain (RTD) appears. The RTD, surrounded by a domain wall, gradually shrinks and finally disappears. The domain wall splits into a pair of disclination lines by increase of the voltage. This work examines the energy dissipation mechanism of annihilation dynamics by ascertaining the phenomenological viscosity Γ based on experimentation. To evaluate Γ, the time dependence of curvature radius R is analyzed using an equation R=Asqrt[t_{0}-t], where A is a fitting parameter. Parameter A decreased linearly with increasing applied voltage and suddenly became constant. Also, Γ was evaluated from A as a function of voltage. When the voltage reaches a critical value, Γ increased sharply to be one order of magnitude greater than that under low voltages. The critical voltage is consistent with the theoretically expected value at which the splitting of domain wall occurs. The transition of Γ is described clearly by localized deformation of the director field.

Shear-enhanced elasticity in the cubic blue phase I

We present results of the linear and nonlinear rheology of the cubic blue phase I (BPI). The elasticity of BPI is dominated by double-twist cylinders assembled in a body-centered cubic lattice, which can be specified by disclination lines. We find that the elasticity of BPI is enhanced by an order of magnitude by applying pre-shear. The shear-enhanced elasticity is attributed to a rearrangement of the disclination lines that are arrested in a metastable state. Our results are relevant for the understanding of the dynamics of disclinations in the cubic blue phases.

Orientation Control of Smectic Liquid Crystals via a Combination Method of Topographic Patterning and In-Plane Electric Field Application for a Linearly Polarized Illuminator

We dynamically controlled the configuration of layering structures built by smectic A liquid crystal molecules using the combination method of the microchannel confinement and the in-plane electric field to realize the linearly polarized illuminator and bistable structures. Once a mild in-plane electric field (∼30 V) is applied between polymeric walls, the layer configuration was changed from the toric focal conic domains to periodic zigzag patterns of alternatively packed focal conic domains. The transformed zigzag patterns maintained their structures even after turning off the applied electric fields, revealing the ability for use in a bistable memory device. Indeed, a strong electric field (∼100 V) can make unidirectionally aligned LC molecules along with the applied electric field via zigzag patterns, and electro-optical performance of resultant textures when the sample is mixed with fluorescent dyes was characterized to show a linearly polarized light illuminator. Our electric field in and on the confined geometries will be used in the fabrication of functional structures built by polar soft materials which can broaden applications in patterning platforms and efficient electro-optical devices in the near future.

Dynamic orientation transition of the lyotropic lamellar phase at high shear rates

The dynamic orientation behavior of the lamellar phase of a triblock copolymer is studied in a wide range of shear rates as a function of solvent composition. We find that various phases can be induced by increasing the shear rate. At low shear rates, the onion phase forms from planar lamellae with many defects. A further increase of the shear rate caused the onion structure to break down, and the lamellar phase recovers with fewer defects. Finally, the transition of the orientation from parallel to perpendicular is observed at high shear rates. In the orientation transition at high shear rates, a stable intermediate structure, to our knowledge, is found for the first time. We also find that the critical shear stress of the rupture of the onion phase coincides with the orientation transition. The consistency of the critical shear stress suggests that all orientation transitions at a high shear rate are dominated by a mechanical balance between the applied viscous stress and the internal relaxation mode of the lamellae.