The recent findings of large electrocaloric effects (ECEs) in ferroelectric polymers and in ferroelectric ceramic thin films have attracted great interest for developing new cooling cycles that are environmental friendly and have the potential to reach better efficiency than the existing vapor‐compression approach. Compared with these solid state ECE materials, a dielectric fluid with a large ECE can be more interesting because it may lead to new cooling cycles with simpler structures than these based on solid state ECE materials. Here it is shown that a large ECE can be realized in the liquid crystal (LC) 5CB near its nematic–isotropic (N‐I) phase transition. 5CB has a large dielectric anisotropy, which facilitates the electric‐field‐induced large polarization change. As a result, a large ECE, i.e., an isothermal entropy change of more than 23.6 J kg−1 K−1 is observed just above the N‐I transition.

We compare the performance of polymer-stabilized cholesteric liquid crystal diffraction gratings for two limits of the polymer morphology:  a one-dimensional array of polymer walls that extend through the grating thickness (“bulk network”), and a thin layer of patterned polymer fibrils localized at one surface (“surface network”). In each case, the polymer is spatially templated by the liquid crystal orientational order, but the depth of the network is dictated by UV absorbance of the liquid crystal and a choice of wavelength used to initiate photopolymerization. Whereas both polymer morphologies yield robust electrically switchable gratings, the surface-stabilized grating operates at lower field thresholds and shorter transition times. However, the patterning of the surface network significantly reduces the contrast between grating on and off states, a limitation that can be potentially offset by employing isotropic monomers index-matched to the liquid crystal.

In the banana-shaped achiral molecular system reported here, 1,3-phenylene bis[4-(3-chloro-4-n-octyloxy-phenyliminomethyl) benzoate] (PBCOB) and 1,3-pbenylene bis[4-(3-fluoro-4-n-octyloxy-phenyliminomethyl) benzoate] (PBFOB), their smectic mesophases, including a switchable banana phase B,, were identified by differential scanning calorimetry (DSC), X-ray scattering and polarizing optical microscopy (POM) studies. Both the left-and right-handed helical domains are spontaneously formed upon cooling from isotropic liquid to the switchable banana phase (B7). The homeotropic alignment and ferroelectric properties of banana-shaped liquid crystal are investigated. The spontaneous polarization for PBCOB is about 50 nC/cm2. Doping the PBCOB with a cyanohydrin-contain chiral smectic liquid crystal resulted in more right-handed helical structures.

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