Microstructure of variable pitch cholesteric films and its relationship with the optical properties

Abstract

A way to make cholesteric films reflecting in a broad wavelength band consists in associating different cholesteric pitches in the same film. In two previous papers, we proposed an efficient method to produce variable pitch films, based on a thermal processing, and we studied the optical properties of these films with respect to the time of processing. In the present paper, we study the microstructure of such films with respect to the processing time by means of transmission electron microscopy. The cholesteric phase is shown to be very well ordered. Within a wide range of annealing times, its periodicity is progressive from one face to the other of the film. A description of the evolution of the structure with respect to the processing time is given, and classified in three stages, corresponding to the three stages already stated from the optical properties. The relationship between the evolution of the structure and the optical properties is discussed. PACS. 61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures -61.30.-v Liquid crystals -61.16.Bg Transmission, reflection and scanning electron microscopy (including EBIC)

Wide‐band reflective polarizers from cholesteric liquid crystals with stable optical properties

“…1,2 Much attention has been recently focused on wide-band reflective polarizers (WBRPs) from cholesteric liquid crystals because they are of great importance for practical applications. [3][4][5] Introducing a pitch gradient is an ideal method for increasing the reflective bandwidth of a cholesteric liquid crystal. The pitch difference is often formed by the molecular diffusion of optically active monomers with different optical reactivities and fixed by photopolymerization.…”

Characteristics of wide-band reflection of polymer-stabilised cholesteric liquid crystal cell prepared from an unsticking technique

“…However, for some specific applications such as full-colour or white-or-black reflective displays, wide-band reflective polarisers are desired. Recently, much attention has focused on non-uniform pitch distribution in PSCLC to obtain a wide-band reflection effect (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). The unsticking technique, having been used in fabricating dichroic sponge polymer dispersed liquid crystal (D-SPDLC) films (25), was introduced into the preparation of wide-band reflective cells in this study.…”

Preparation and reflectance properties of new cholesteric liquid crystalline copolymers containing cholesteryl group

“…It has been demonstrated that introducing a pitch gradient (or forming a pitch difference) is an ideal method for increasing the reflection bandwidth of a Ch-LC [4,5]. Some widely investigated examples can be found in previous reports [4][5][6][7][8][9][10][11][12][13][14][15][16]. Recently, the choice of polymer stabilized cholesteric liquid crystals (PSCLCs) elaborated under specific ways has offered an important route to increase the reflection bandwidth [4][5][6][7][8][9][10][11][12][13].…”