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.
We investigate the role of competing nonlinear responses in the formation and propagation of bright spatial solitons. We use nematic liquid crystals (NLCs) exhibiting both thermo-optic and reorientational nonlinearities with continuous-wave beams. In a suitably prepared dye-doped sample and dual beam collinear geometry, thermal heating in the visible affects reorientational self-focusing in the near infrared, altering light propagation and self-trapping.
We demonstrate a new successful technique for inducing a monodomain in blue phase (BP) liquid crystals (BPLCs). By application of an AC voltage during the cooling or heating of the material into the BP temperature range, a fairly homogeneous BP area was obtained, compared to the case without voltage. We determined that applying a voltage of 3.3V/mu m was very effective in terms of obtaining a monodomain: for four of the seven different applied cooling/heating rates an area ratio of more than 99% was obtained for one particular BP orientation. This study describes a successful and replicable technique to make a BPLC monodomain, which is important for the development of BPLCs and other applications
In this Letter, we report on measurements of the complex permittivity of highly anisotropic nematic liquid crystals at microwave frequencies as a function of the AC bias voltage. Permittivity measurements have been performed by the split post dielectric resonator technique. The experiments have shown that when the AC bias voltage increases from 0 to 8 V, the real part of the permittivity of these liquid crystals changes by up to 28%. The tunability and the relatively low dielectric losses observed in these liquid crystal mixtures mean that they are ideal materials for the design of tunable microwave components.
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