Investigations of the mixtures of semiconducting quantum scale particles in anisotropic liquid crystal (LC) medium have become a vibrant area of research primarily due to their very interesting phenomenology. The results of these investigations fall into four groups: (i) Photoluminescent emissive properties of the quantum particles ordinarily depend on the size, shape, and chemical nature of the particles. These undergo important changes in their spectrum, polarization, and isotropy of emission when dissolved in an anisotropic LC phase. Moreover, their response to external stimuli such as mechanical, optical, or electric fields is altered in important ways; (ii) physical properties of LCs such as viscosity, dielectric relaxation, etc are modified by the addition of quantum particles. Their presence in ferroelectric smectic LC is known to give rise to an antiferro- to ferri-electric phase transition and suppresses the paraelectric phase; (iii) switching characteristics of LC devices are altered in important ways by the addition of quantum particles. Their threshold voltage is usually lowered, contrast ratio, and switching speed of nematic, ferroelectric, and cholesteric devices may increase or decrease depending on the concentration, applied field, and particle anisotropy; and (iv) controlled aggregation of quantum particles at the interface between isotropic and LC domains, near added polystyrene beads, and in the vicinity of point defects gives rise to interesting photonic structures, enables studies of photon antibunching and single photon sources. Clearly, there is a need to understand the basic and applied aspects of these systems and find routes to their technological applications including sensors, electrooptical devices, and solar energy harvesting. This review provides an overview of recent work involving liquid crystals and a variety of quantum particles.

The mechanism responsible for liquid crystal (LC) alignment on mechanically buffed or UV exposed polymer films is poorly understood. A comprehensive study of LC alignment on variously prepared substrates unequivocally shows that the anisotropy in the surface roughness of the substrate completely determines the direction of LC alignment. In all the cases studied, including those where an anchoring transition occurs with temperature, the LC director (re)aligns in the directions of low roughness.

Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature of domain structure, microscopic smectic phase structure, relaxation mechanism, and sample history. These aspects of liquid crystal elastomers are briefly reviewed followed by a summary of the results of recent elastic and high-resolution X-ray diffraction studies of the shape memory effect and the dynamics of the formation of the smectic-C chevron-like layer structure. A possible route to realizing auxetic effect at molecular level is also discussed.

Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 Å between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from ∼35 to 42 Å in the orientationally ordered nematic ($N$) phase and from 27 to 32 Å in the columnar or middle ($M$) phase having long range lateral positional order. The assemblies’ length depends on concentration and consists of ∼23 molecules in the $N$ phase, becoming three to ten times larger in the $M$ phase. The scission energy is concentration dependent in the $N$ phase with values ∼7.19 ± 0.14 $k_{B}T$ (15 wt %), 2.73 ± 0.4 $k_{B}T$ (20 wt %), and 3.05 ± 0.2 $k_{B}T$ (25 wt %). Solutions of all concentrations undergo a spinodal decomposition at temperatures above ∼40 °C, resulting in DSCG-rich regions with the $M$ phase and water-rich regions in the $N$ and isotropic phases.

The effect of well-established homeotropically and homogeneously aligning polyimides, developed for calamitic liquid crystals, on the alignment of the nematic phases of bent-core mesogens was investigated using polarizing optical microscopy and conoscopy. Two polyimides, the homogeneously aligning SE7792 and the homeotropically aligning S659, were used to align three bent-core mesogens. Two of the mesogens, with an azo group in one of their arms, are found to align in a manner similar to the calamitic mesogens, while a fluorenone core based mesogen counter-intuitively aligns homogeneously on S659 coated surface and homeotropically on SE7792. Attractive interactions between unidirectionally oriented polyimide side-chains and the alkyl chains of mesogens determine the direction of alignment of the nematic director.

The temperature dependence of the orientational order parameters $\langle P_2\left(\cos \beta \right)\rangle$ and $\langle P_4\left(\cos \beta \right)\rangle$ in the nematic ($N$) and twist-bend nematic $\left(N_{\mathrm{tb}}\right)$ phases of the liquid crystal dimer CB7CB have been measured using x-ray and polarized Raman scattering. The $\langle P_2\left(\cos \beta \right)\rangle$ obtained from both techniques are the same, while $\langle P_4\left(\cos \beta \right)\rangle$, determined by Raman scattering is, as expected, systematically larger than its x-ray value. Both order parameters increase in the $N$ phase with decreasing temperature, drop across the $N-N_{\mathrm{tb}}$ transition, and continue to decrease. In the $N_{\mathrm{tb}}$ phase, the x-ray value of $\langle P_4\left(\cos \beta \right)\rangle$ eventually becomes negative, providing a direct and independent confirmation of a conical molecular orientational distribution. The heliconical tilt angle α, determined from orientational distribution functions in the $N_{\mathrm{tb}}$ phase, increases to $\sim {24}^{\circ }$ at $\sim 15$ K below the transition. In the $N_{\mathrm{tb}}$ phase, $\alpha \left(T\right)\propto {(T^{*}-T)}^{\lambda }$, with $\lambda =0.19\pm 0.03$. The transition supercools by 1.7 K, consistent with its weakly first-order nature. The value of λ is close to 0.25 indicating close proximity to a tricritical point.