Thermal Switching of the Reflection in Chiral Nematic Mesoporous Organosilica Films Infiltrated with Liquid Crystals

Abstract

Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays.

Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

“…Moreover, due to the helical internal structure, the reflected light is circularly polarized with the same handedness as the helix (Dumanli et al, 2014;Lagerwall et al, 2014;Park et al, 2014). These photonic films have immediate application potential in many photonic materials and devices, e.g., in security papers for anti-counterfeiting purposes (Tabor et al, 2012), sensors (Giese et al, 2013a;Zhang et al, 2013), or in mirrorless lasing (Lagerwall et al, 2014;Wenzlik et al, 2014). Further enhancements are possible by letting the liquid crystalline order organize guest nanoparticles Liu et al, 2014;Nguyen et al, 2014;Querejeta-Fernandez et al, 2014) or template an inorganic or other organic phase that is synthesized within the polysaccharide suspension (Shopsowitz et al, 2010(Shopsowitz et al, , 2012a(Shopsowitz et al, ,b, 2014Kelly et al, 2012;Giese et al, 2013b;Khan et al, 2013).…”

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

“…We are currently experiencing an increasing interest in gas sensors based on liquid crystals (LCs) [32][33][34][35][36][37][38][39][40][41], functioning at room temperature, requiring no energy supply as they are powered by thermal energy alone, and delivering a strong optical response that is easily detected without complex spectroscopic equipment. The response is due to the ability of certain gas molecules, even at low concentration, to strongly influence the liquid crystal self-assembly [40,[42][43][44][45], triggering a reorientation of the liquid crystal director [32,34,43,44], a change in period of the supramolecular helix of shortpitch cholesterics [19,36,42,[46][47][48], or even complete loss of long-range ordering [11].…”

“…In these cases the LC sensor response arises from an analyte-induced change of anchoring conditions, leading to a major change in director field geometry within the sample, which in turn results in a strong change in optical properties. Other researchers [37,38,41] have demonstrated alternative approaches for exploiting LCs as sensors to chemical agents, sensitised either through doping or other chemical modifications.…”

Liquid Crystals of Cellulosics: Fascinating Ordered Structures for the Design of Functional Material Systems

“…It was possible to vary the structural color, derived from the chiral nematic pitch of the hybrids, across the entire visible spectrum by simply changing the CNC/silica composition or by modifying the preparation conditions. They successfully assigned diverse functionalities to the chiral nematic mesoporous silicas by loading organic or inorganic functional guest substances into the mesopores [135][136][137]. Scheme 5 outlines the preparation protocol used.…”

“…The above results demonstrating many colorful materials could hold much appeal, but attention should be called to the fact that all the materials based on CNC chiral mesomorphy share the common feature of preserving a left-handed Loading 4-cyano-4'-octylbiphenyl into the mesopores [136] Polymerization of conjugated polymer in the mesopores [137] Removal of CNC via calcination or acid hydrolysis…”