Experimental studies on the rheology of cubic blue phases

Abstract

We report detailed experimental studies on the rheology of cubic blue phases. We observe several flow regimes within each blue phase from rheomicroscopy and small angle light scattering experiments. Both the cubic blue phases exhibit solid-like response while the cholesteric phase shows gel-like behavior. The elastic modulus of BP-I is larger than that of BP-II. The shear induced yield transition occurs at a higher strain in BP-II than BP-I. Both the blue phases show stress relaxation through periodic modulation in step-strain experiments. Our results show that the rheological responses of these two phases are significantly different owing to the distinct networks of defect-disclinations.

Nonlinear Rheology and Fracture of Disclination Network in Cholesteric Blue Phase III

“…Similar viscosity curve for COC was presented by some researchers [30,31]. The steep increase in the viscosity during cooling and heating process is attributed to the formation of BPs [14,15]. As Henrich et al presented in their numerical simulation, the viscous stress response of BPs is significantly affected by the deformation of the disclination lines in BPs [18].…”

“…Similar viscoelastic properties, the existence of the plateau modulus and slow relaxation have been reported for soft solid-like materials such as concentrated emulsion, silica suspensions and biopolymer network systems [34][35][36]. Soft solid-like behavior has been similarly reported for BPI [14,15].…”

“…The increase in the viscosity is therefore a characteristic feature of the formation of BPs with disclination networks. It is expected that not only BPIII but also BPI and BPII show the increase of the viscosity when they are formed from isotropic and chiral nematic phases [14,15]. …”

Microfluidic flow of cholesteric liquid crystals

“…Finally, the apparent viscosity declines in all cases. This is expected as all systems we consider should shear thin, as found both in other simulations and experimentally 47 . The decrease of the apparent viscosity with increasing pressure gradient is more gradual for BPII than for CF1, which reflects the gradually dissolving DTC structure in the former.…”

“…We characterise the sequence of dynamical, flowinduced regimes, which we predict CF1 and BPII structures should display when subjected to a pressure driven flow in a microfluidic geometry with controlled anchoring conditions. Such experiments are now feasible, with techniques similar to those reported in a recent experimental work 47 . For CF1s we only considered strong and weak homeotropic anchoring conditions, as these are crucial for obtaining a stable CF1 phase without flow.…”