Preparation and thermo-optical characteristics of a smart polymer-stabilized liquid crystal thin film based on smectic A–chiral nematic phase transition

Abstract

A smart polymer stabilized liquid crystal (PSLC) thin film with temperature-controllable light transmittance was prepared based on a smectic-A (SmA)–chiral nematic (N*) phase transition, and then the effect of the composition and the preparation condition of the PSLC film on its thermo-optical (T-O) characteristics has been investigated in detail. Within the temperature range of the SmA phase, the PSLC shows a strong opaque state due to the focal conic alignment of liquid crystal (LC) molecules, while the film exhibits a transparent state result from the parallel alignment of N* phase LC molecules at a higher temperature. Importantly, the PSLC films with different temperature of phase transition and contrast ratio can be prepared by changing the composition of photo-polymerizable monomer/LC/chiral dopant. According to the competition between the polymerization of the curable monomers and the diffusion of LC molecules, the ultraviolet (UV) curing surrounding temperature and the intensity of UV irradiation play a critical role in tuning the size of the polymer network meshes, which in turn influence the contrast ratio and the switching speed of the film. Our observations are expected to pave the way for preparing smart PSLC thin films for applications in areas of smart windows, thermo-detectors and other information recording devices.

Nature‐Inspired Emerging Chiral Liquid Crystal Nanostructures: From Molecular Self‐Assembly to DNA Mesophase and Nanocolloids

“…Using this methodology, Kent Optronics developed a product named as e-TransFlector, such an electrically switchable transreflective LC device can be rapidly and reversibly switched between full-color reflection, half-reflection, and fully transparent states through applying a low electric field as shown in Figure 5d-f. Several other research groups have also put extensive efforts to develop the cholesteric films with switchable reflection bandwidth. [99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115] For example, Schenning and co-workers reported electrically switchable broadband photonic reflection in infrared regions by developing polymer network-stabilized cholesteric thin films. [99,100] White and co-workers found that broadband photonic reflection could be dynamically switched in polymer stabilized cholesteric LCs with negative dielectric anisotropy under DC electric fields, Figure 3.…”

“…[108] These adaptive devices allow the maximum infrared light to enter in winter while efficiently reflect solar infrared light in summer, which holds great potential in architectural and automotive applications with intelligent adaptability and energy efficiency. [108][109][110][111][112]…”

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

“…These properties led to a range of CLC materials that are responsive to various stimuli (e.g. light, electric field, or temperature) and change properties such as reflectivity or surface topography . For the fabrication of stimulus‐responsive LC polymer films, both polymer liquid crystalline elastomers and glassy networks have been used …”

Effects of polymer network on electrically induced reflection band broadening of cholesteric liquid crystals

“…They affected the polymer network morphology and then broadening through the viscosity. It might also influence the broadening through other factors such as the molecular size, polarity, solubility, and other properties of the chiral dopants …”

“…The liquid crystal has a positive dielectric anisotropy and change orientation when an external electric field is applied. This type of polymer stabilized CLCs have been used to make a variety of optical devices such as displays, high‐efficiency filters, and smart windows . In these devices, the polymer network produces a pitch gradient or a non‐uniform pitch distribution with thermal or optical stimuli, template, and micro‐gel blending .…”