The behaviour of the anisotropic electrical conductivity of liquid crystal–gold nanoparticle (LC‐GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol‐capped GNPs has been investigated. The nematic–isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ_∥) and orthogonal (σ_⊥) to the director shows a much smaller but definite decrease as X increases.

We report complex permittivity characteristics in composites of gold nanoparticles (GNP) and a weakly polar nematic liquid crystal possessing a low frequency director relaxation. Differential calorimetric measurements show that the inclusion of GNP has a strong influence on the isotropic–nematic (fluid–orientational fluid) transition temperature as well its first order character in terms of the transition entropy. The absolute value of conductivity increases by two to three orders of magnitude with respect to that for the host liquid crystal and its concentration dependence is demonstrated to be described by the percolation scaling law generally observed in composites of metal particles and polymers. However, the obtained exponent is much smaller, possibly owing to thermal fluctuations present in the fluid-like nematic medium. The activation energy governing the temperature dependence of conductivity is much higher in the nematic than in the isotropic phase. The frequency dependence of the ac conductivity exhibits a critical frequency that is concentration-dependent, but the exponents obtained defy Jonscher's Universal Response principle. A surprising feature is the observation of a substantial increase of not only the principal permittivity values, but their anisotropy as well. These studies also constitute the first report on the influence of GNP on the director relaxation mode of nematics. In contrast to the behaviour of the static permittivity, the dynamics of the system as measured using the director relaxation is seen to become faster with the presence of GNP. We provide an explanation for this antagonistic behaviour in terms of the alignment of the liquid crystal molecules in the vicinity of GNP, and the importance of the weak polarity of the liquid crystals used.

Existing liquid crystal (LC) smart window technologies are yet to make inroads into the consumer market largely due to more than 50% of the cost-share of the tin-doped indium oxide (ITO) layer used as the transparent conducting electrode (TCE). In this work, we demonstrate the deployment of a low-cost hybrid TCE as a pathbreaking alternative to ITO in LC smart windows with no compromise in device performance in comparison to standard ITO-based devices. Theoretical modeling puts on a firmer ground the concept of a thin, moderately conducting layer superposed on a micro/nano wire mesh to achieve a uniform electric field, imperative for the efficient operation of LC devices. To illustrate its innovative features, a large-area (10 × 10 cm²) polymer dispersed LC smart window is devised using a hybrid TCE fabricated by spray-coating SnO₂ over an Al mesh formed by the self-crack templating method. The device exhibits a high transparency modulation of ∼94% without any degradation even after 400 days. Further, a new idea of a window-cum-display (60 × 50 cm²) with twelve as-fabricated devices assembled in a 4 × 3 matrix having individual and remote control of each row is demonstrated. Bearing commercialization aspects in mind, the entire fabrication is made industry compatible and scalable.

We have synthesized four different types of dimesogenic compounds involving the cholesteryl moiety as one of the mesogenic constituents, and have investigated their liquid crystalline properties. The molecular structures of these dimesogens have been confirmed by spectral analyses; they exhibit a rich polymorphism, as revealed by optical microscopic and differential scanning calorimetric observations. The studies show that the mesomorphic behaviour is sensitive to the nature of the terminal alkyl chains, and to the structure of the 'second mesogen' that is attached to the cholesteryl unit through a polymethylene spacer.