Cholesteric Liquid Crystalline Films Research Articles

Fabrication of Polymer/Cholesteric Liquid Crystal Films and Fibers Using the Nonsolvent and Phase Separation Method.

In recent years, liquid crystal materials have drawn great interest because of their wide range of applications. Among various thermochromic materials, cholesteric liquid crystalline (CLC) materials have been well studied and reported. CLC materials have the advantages of ready manipulation and multiple color transitions. For the further development of smart clothing and wearable electronics, however, the incorporation of CLC materials into polymers still remains challenging. The difficulties lie in the prevention of leakage of CLC and retention of the cholesteric liquid crystalline phase. In this work, we demonstrate a versatile nonsolvent and phase separation method using polar solvents to incorporate CLC microspheres into polymer matrix. Poly(vinyl alcohol) (PVA), a water-soluble polymer, is chosen as the polymer because of its high transparency and ease to handle. Using spin-coating and wet spinning techniques, PVA/CLC films and fibers can be fabricated. The formation of CLC microspheres in the polymer matrix is characterized through optical and polarized microscopy. Compared with the CLC films, the PVA/CLC composites demonstrate superior thermal stability. Moreover, both PVA/CLC films and fibers exhibit good color stability from the electrical tests. This work provides an effective strategy to prepare polymer/CLC composites, paving a wide avenue toward applications in smart textiles, display technologies, and medical devices.

Dual mechanochromism of cellulosic cholesteric liquid-crystalline films: wide-ranging colour control and circular dichroism inversion by mechanical stimulus

We found that cellulosic liquid-crystalline films displayed not only a wide-ranging colour change but also inversion of circular dichroism upon a mechanical stimulus.

Experimental Investigation of the Polarization Plane Rotation of Light in Cholesteric Liquid-Crystalline Film with an Anisotropic Defect Layer

This paper experimentally demonstrated that in the cholesteric liquid-crystalline films it is possible to induce defect, which can be controlled by external electric field. Three cases of induced defects were examined and the main result of the experiment is that the rotation of polarization plane has maximum value when light first propagates through chiral liquid-crystalline photonic structure and then falls to the anisotropic layer. We have also supporting calculations, showing an agreement between experimental results and theoretical calculations. We present a new liquid crystal device configuration that performs as a tunable linear polarizer for both polarized and unpolarized lights.

UV irradiation gradient induced banded texture in photo-polymerized ethyl-cyanoethyl cellulose/poly(acrylic acid) cholesteric liquid crystalline films and patterns fabrication thereof

The photo-polymerization-induced banded texture of ethyl-cyanoethyl cellulose/acrylic acid/copper acrylate ((E-CE)C/AA/CuAA2) cholesteric liquid crystalline (CLC) solutions were investigated. The results indicate that the CLC phase can be fixed by the photo-polymerization. Banded texture was obtained in the photo-polymerized CLC films. The orientation of the banded texture induced by the photo-polymerization depends on the gradient of UV irradiations on the surface of the (E-CE)C/AA/CuAA2 CLC solutions. CLC films with different patterns can be obtained by introducing the UV irradiation gradient on the (E-CE)C/AA/CuAA2 CLC solutions surface by using masks with different patterns. The simple approach for the fabrication of CLC films with different patterns may have the potential application in the fields of holographic image storage.

Circular Differential Scattering of Light in Films of Chiral Polyfluorene

Circular differential transmission in thick films (1.1 mum) of poly{9,9-bis[(3S)-3,7-dimethyloctyl]-2,7-fluorene} is investigated. The vitrified liquid crystalline film obtained after annealing shows high circular differential transmission of light in the wavelength range where the polyfluorene does not absorb (lambda > 450 nm). Using a specifically designed chiroptical setup, we show that circular selective reflection of light in which the circular polarization of the light is retained after reflection, a process which is characteristic for cholesteric liquid crystalline films, makes a negligible contribution to the differential transmission. Using an integrating sphere, we show that circular differential scattering can account for the observed circular differential transmission for lambda > 450 nm.

Rotational Reorganization of Doped Cholesteric Liquid Crystalline Films

In this paper an unprecedented rotational reorganization of cholesteric liquid crystalline films is described. This rotational reorganization results from the conversion of a chiral molecular motor dopant to an isomer with a different helical twisting power, leading to a change in the cholesteric pitch. The direction of this reorganization is correlated to the sign of the change in helical twisting power of the dopant. The rotational reorganization of the liquid crystalline film was used to rotate microscopic objects 4 orders of magnitude larger than the bistable dopants in the film, which shows that molecular motors and switches can perform work. The surface of the doped cholesteric liquid crystalline films was found to possess a regular surface relief, whose periodicity coincides with typical cholesteric polygonal line textures. These surface features originate from the cholesteric superstructure in the liquid crystalline film, which in turn is the result of the presence of the chiral dopant. As such, the presence of the dopant is expressed in these distinct surface structures. A possible mechanism at the origin of the rotational reorganization of liquid crystalline films and the cholesteric surface relief is discussed.

Controlling the Color of Cholesteric Liquid‐Crystalline Films by Photoirradiation of a Chiroptical Molecular Switch Used as Dopant

AbstractUsing thin films of a cholesteric mixture of acrylates 2 and 3 doped with the chiroptical molecular switch (M)‐trans‐1, photocontrol of the reflection color between red and green is possible. This doped liquid‐crystal (LC) film can be used for photoinduced writing, color reading, and photoinduced locking (via polymerization) of chiral, optically written information.