Temperature dependent light transmission-light scattering switching of (homeotropic liquid crystalline polymer network/liquid crystals/chiral dopant) composite film

A (photo-polymerizable liquid crystal (LC) monomer/LCs/chiral dopant/photoinitiator) mixture with a smectic A (SmA)-chiral nematic (N*) phase transition was sandwiched between two ITO glass substrates which were not subjected to any surface orientation treatment. When an electric field-induced homeotropically oriented SmA phase of the mixture was irradiated with UV light, an oriented liquid crystalline polymer (LCP) network was formed upon photo-polymerization of the LC monomer. Then, a (homeotropically oriented LCP network/LCs/chiral dopant) composite with a SmA-N* phase transition was prepared. A focal-conic texture appeared in the heat-induced N* phase of the composite upon heating from the transparent state of the homeotropically oriented SmA phase; the focal-conic texture exhibited strong light scattering. Upon cooling the composite to the SmA phase, this phase was again homeotropically oriented due to the strong intermolecular interaction between the LC molecules and the homeotropically oriented LCP network. Thus, the transparent state of the SmA phase and the light scattering state of the N* phase occurred reversibly upon cooling and heating, accompanied by the thermal SmA-N* phase transition.     

Electrically induced and thermally erased properties of side-chain liquid crystalline polymer/liquid crystal/chiral dopant composites

The properties of synthesized side-chain liquid crystalline polymer (SCLCP)/liquid crystal (LC)/chiral dopant composites having a chiral nematic (N*) phase at room temperature were investigated by polarized optical microscopy (POM) and a UV/VIS/NIR spectrophotometer. The composite exhibited a planar texture after it was filled into cells under homogeneous boundary conditions and it was transparent. When an electric field was applied to the composite, a focal conic texture was formed and the composite became light scattering. After the electric field was turned off, the light-scattering state remained stable for some time, i.e. the light-scattering state exhibited a memory effect. The focal conic texture changed into the planar texture when the composite was heated and the composite became transparent again. Therefore, the composite had electrically induced and thermally erased properties. The SCLCP had some influence on the memory effect and on the thermo-electro-optical properties of the composite.     

Copolymer composition-dependent light transmission of polymer/liquid crystals composite films

Electrooptic responses (voltage and angular-dependent transmittance) of polymer/liquid crystal composite films with H, V, and unpolarized lights have been studied based on a nematic liquid crystal (Ro-5921) and four types of homopolymers and copolymers from ethyl methacrylate and styrene with different compositions. In this way, the index ratio of the polymer (n_p) to the ordinary refractive index of liquid crystal (n_o)(n_p/n_o) has been varied systematically, and the effect of the index ratio on viewing angle, applied voltage, response times, and transient response have been investigated. With increasing styrene content in the copolymer, droplet size increased, threshold (V_th) and saturation (V_sat) voltage, and rise time decreased. With n_p ≲ n_o, maximum transmittance occurred at normal incidence, regardless of the type of polarization. On the contrary with n_p > n_o, V-polarization gave a peak in the transmittance-voltage curve, and transmittance overshot upon removal of the field, and these were interpreted in terms of effective refractive index and two-step relaxations. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 55–64, 1998     

Electrically induced and thermally erased properties of side‐chain liquid crystalline polymer/liquid crystal/chiral dopant composites

The properties of synthesized side‐chain liquid crystalline polymer (SCLCP)/liquid crystal (LC)/chiral dopant composites having a chiral nematic (N*) phase at room temperature were investigated by polarized optical microscopy (POM) and a UV/VIS/NIR spectrophotometer. The composite exhibited a planar texture after it was filled into cells under homogeneous boundary conditions and it was transparent. When an electric field was applied to the composite, a focal conic texture was formed and the composite became light scattering. After the electric field was turned off, the light‐scattering state remained stable for some time, i.e. the light‐scattering state exhibited a memory effect. The focal conic texture changed into the planar texture when the composite was heated and the composite became transparent again. Therefore, the composite had electrically induced and thermally erased properties. The SCLCP had some influence on the memory effect and on the thermo‐electro‐optical properties of the composite.     

Photochromism in mixtures of liquid crystalline chiral copolymers with a photosensitive chiral dopant

Mixtures of a photosensitive chiral dopant based on ( )-menthone with left-handed and righthanded cholesteric copolymers were prepared. The phase behaviour and optical properties of the mixtures prepared were studied. The action of UV radiation on planar oriented films of such systems was shown to induce dramatic changes in the maximum reflection wavelength as a result of E-Z isomerization of the dopant molecules. The kinetics of photoisomerization of such mixtures in solution and in the bulk were investigated at different temperatures. The above mixtures can be considered as promising and uprecedented materials for coloured data recording and storage.     

Thermo-recording in (side chain type smectic A liquid crystal polymer/nematic liquid crystal/chiral dopant/dichroic dye) composite with a low power laser

Thermo-recording in a [side chain type smectic A liquid crystal polymer (SmA-LCP)/nematic liquid crystal (N-LC)/chiral dopant/dichroic dye] composite has been realized by using 2mW of power from a He-Ne laser. The laser irradiation-induced phase transitions of smectic A (SmA) → chiral nematic (N*) → SmA formed the dominant thermo-recording mechanism in the composite. Thermo-recording in the (SmA-LCP/N-LC/chiral dopant/dichroic dye) composite exhibited a higher contrast when compared with the non-polymeric (SmA-LC)/N-LC/chiral dopant/dichroic dye composite.     

Time‐dependent deformation of structurally chiral polymer networks in stabilized cholesteric liquid crystals

Polymerization of crosslinkable liquid crystal monomers in chiral liquid crystalline media stabilizes the phase and enables distinct electro‐optic properties relative to small‐molecule analogs. Particularly interesting are cases where the polymerization forms a crosslinked polymer network that maintains a “structural” chirality. Recent reports have employed this methodology to realize a diverse set of electro‐optic responses in polymer stabilized cholesteric liquid crystals (PSCLCs) including reflection bandwidth broadening, reflection wavelength tuning, and dynamic scattering modes. It has been proposed that the mechanism at the root of these electro‐optic responses is an ion‐mediated, electromechanical deformation of the stabilizing and structurally chiral polymer network. In an effort to better understand the nature of these deformations, here we have characterized the electro‐optic response of PSCLCs with different polymer concentrations and crosslink densities. The dynamic response of PSCLCs to electric fields exhibits a time‐dependent behavior reminiscent of the creep of polymeric materials to mechanical deformations. The electro‐optic response can be described as the superposition of two contributions: the fast deformation of a relatively soft component of the polymer network (1–2 s) and the slower (10–20 s) deformation of a harder component. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1087–1093     

The phase behaviour and optical properties of a nematic/chiral dopant liquid crystalline mixture system

The phase behaviour and aggregation states of a binary mixture of a nematic liquid crystal and a chiral dopant have been investigated. The nematic liquid crystal E7 was miscible with the chiral dopant S811 over their entire concentration range. Binary E7/S811 mixtures formed the N* phase for S811 contents under 20%, and the SmA* phase for S811 contents between 40% and 90%. BP and TGBA* frustrated phases were found during cooling, for S811 contents between 25% and 35%. The helical pitches of the binary mixtures decreased with increasing chiral dopant content. From XRD profiles, the orientational ordering of the binary composites was found to increase with increasing chiral dopant content.     

Monitoring kinetic processes in polymer solutions with time dependent static light scattering (TDSLS)

An overview of recent developments in TDSLS and auxiliary techniques is given. This includes background theory, and examples of results and applications for online monitoring of polymerization reactions, kinetics and structural determinations from degrading polymers, aggregation, and dissolution of dry polymer powders. Also, automatic dilution techniques allow for continuous characterization of the equilibrium states of multi-component solutions. Illustrations are given for the case where the change in polyelectrolyte dimensions, interactions and hydrodynamics can be probed.     

Temperature effect on the rubbing-induced optical phase retardation of a side group liquid crystalline polymer film

Recently we observed an unusual temperature dependence of the pretilt angle of a nematic liquid crystal generated at the rubbed surface of a side group liquid crystalline polymer film. To understand the mechanism, a detailed investigation of the temperature effect on the rubbing-induced optical phase retardation of a side group liquid crystalline polymer film has been carried out. On heating the film above the glass transition temperature of the polymer, a clear change is seen in the temperature dependence of the optical phase retardation. We infer from this investigation that the thermal variation of the rubbing-induced optical phase retardation results in a change in the temperature variation of the pretilt angle.     

Temperature effect on the rubbing-induced optical phase retardation of a side group liquid crystalline polymer film

Recently we observed an unusual temperature dependence of the pretilt angle of a nematic liquid crystal generated at the rubbed surface of a side group liquid crystalline polymer film. To understand the mechanism, a detailed investigation of the temperature effect on the rubbing-induced optical phase retardation of a side group liquid crystalline polymer film has been carried out. On heating the film above the glass transition temperature of the polymer, a clear change is seen in the temperature dependence of the optical phase retardation. We infer from this investigation that the thermal variation of the rubbing-induced optical phase retardation results in a change in the temperature variation of the pretilt angle.     

The thermally sensitive characteristics of a (smectic LCP/ nematic LC/chiral dopant) ternary composite system

A transition between the transparent smectic A (SmA) phase and the light scattering chiral nematic (N*) phase was realized based on the thermally induced SmA N* phase transition for the homeotropically aligned \[liquid crystalline polymer (LCP)/liquid crystal (LC)/chiral dopant] ternary composite system. The LCP played an important role in increasing the intensity of the light scattering of the heat-induced N* phase. Meanwhile the effects of the composition of the ternary composite system on the thermo-optical characteristics were also investigated.     

Doping effects of fluorinated chiral dopant in blue phase liquid crystals and its electro-optical behavior

ABSTRACT

We reported a fluorine-containing binaphthyl derivative, denoted as BD-F, which showed a low helical twisted power. The blue phase liquid crystal (BPLC) doped with BD-F achieved a lower operating voltage than that only used traditional chiral dopant, resulting from the larger dielectric property of fluorinated BD-F. In addition, the BPLC composite exhibited a wider temperature range and an enhanced Kerr effect with the decreased frequency. In terms of the applications, the devices revealed microsecond response time, thereby providing broad prospects for photonics and displays.     

Temperature dependent study of rayleigh wing scattering in liquid acetonitrile

The results of a study on the temperature dependence of the Rayleigh wing scattering in liquid acetonitrile are presented. It was found that the relaxation times increase with rising temperature, a result which is in contradiction to the internal viscosity picture, which has been used to explain the high frequency wing scattering. However, a calculation utilizing a simple cell model of liquids produces results that are in reasonable agreement with experiment.     

Multiple scattering of light from polymer dispersed liquid crystal material

Light scattering from polymer dispersed liquid crystal (PDLC) material has been studied experimentally and by Monte Carlo simulation. Light scattering was measured as a function of both scattering angle and cell thickness. The cell thicknesses of practical interest are in an intermediate regime where neither single scattering nor light diffusion applies. Both the angular and the thickness dependence of the scattering intensity can be described accurately by a Monte Carlo simulation of multiple scattering from a homogeneous distribution of independent scatterers. The model smoothly interpolates between the single scattering limit for thin cells and the diffusion limit for thick cells. It can easily be extended to include any specific feature of a scattering display system.     

Fourier-transform infrared study of the switching process in a ferroelectric liquid crystalline polymer

The implementation of the step-scan technique on our FT-IR spectrometer enabled us to follow the electric-field induced reorientation dynamics of different molecular segments of a ferroelectric liquid crystalline polymer on a sub-millisecond time scale. It was detected that not only the mesogen but also the spacer and at least part of the backbone take part in the reorientation process.     

Temperature behaviour of a liquid crystal comb polymer: Light scattering and noise of the scattered light

Measurements of the intensity of the monochromatic light transmitted through and scattered by a comb polymer with a polyacrylamide main chain were performed between room temperature and the isotropization temperature of the polymer. The stationary noise of the light scattered at low angle was measured in the same temperature interval. The transmitted intensity is observed to increase strongly above the smectic S_I2-S_c2 transition, where the intensity of the light scattered at low angles is maximized. The power dissipated by the molecular fluctuations dramatically increases above the transition between the two smectic phases. The spectral density curves display a Lorentzian character only below the S_I2-S_c2 transition. At higher temperatures, a more complex frequency behaviour of the stationary noise spectra is observed. Such a behaviour is interpreted in terms of a model explicitly invoking the effect of the Brownian movement of segments of the main chain (backbone) of the polymer on the side chain fluctuations. The parameters governing the Brownian movements of both main and side chains, and their evolution with temperature, are determined and discussed in the light of a simple structural model.     

Electropolymerization rates of polythiophene/polypyrrole composite polymer with some dopant ions

Pyrrole, thiophene, and a mixture of the two monomers were electrochemically polymerized to investigate polymerization rates and the morphology change of the polymer matrix, and to improve the aging and cyclic voltammetric behaviors of the polymers. Thiophene was polymerized on a smooth surface of Pt electrode by two steps. The first step was controlled by electron transfer at the electrical double layer and the other by diffusion of the monomer reacting on the immobilized layer consisting of the precoated thiophene polymer. The electropolymerization rate of the second step was 1.85 × 10⁻⁴ cm³ mol⁻¹ s⁻¹, which is faster by 8.63 × 10² times than the first step. Some supporting electrolytes such as KPF₆, LiClO₄, TBAP, and TBABF₄ were employed in the polymerization reaction to see the effects of dopant anions on the polymerization rate, and KPF₆ was the fastest one at 2.41 × 10⁻⁶ cm s⁻¹. However, owing to its sensitivity to oxygen, LiClO₄ was used for the polymerization that is fairly stable in air and the same rate as KPF₆. For the competitive polymerization reaction of the two monomers the rate of thiophene was found to be about 11 times slower than that of thiophene alone. When the starting concentration of the thiophene monomer was higher than pyrrole by five times, its portion in the composite polymer was found to be only 8–10%. However, this level gave desirable results in terms of redox properties and aging. The resistance against aging was explained by the morphology change, which came from great shrinking of its porosity. © 1997 John Wiley & Sons, Inc.     

Fabrication of flexible light shutter using liquid crystals with polymer structure

We fabricated a light shutter using plastic substrates for high visibility of a flexible see-through display. To achieve a flexible light shutter using liquid crystals (LC), it is essential to maintain the cell gap when the light shutter is bent. We studied methods to fabricate flexible LC light shutters using plastic substrates. We demonstrated light shutters that are initially transparent and flexible with or without polymer walls. We have elucidated that polymer walls and networks provide mechanical stability against the bending of an LC light shutter without any degradation in the electro-optic characteristics. We predict that a flexible light shutter provides not only high visibility but also mechanical stability to a flexible see-through display by positioning it at the back of a flexible see-through display panel.     

Novel liquid crystalline structures of a chiral side chain polymer and its phase transitions

Two novel smectic bilayer structures have been identified in an enantiomerically enriched chiral side chain polymer containing the highly dipolar nitrile group at stereocentres. The structures were characterized by electron diffraction, electron microscopy, and X-ray diffraction. In both phases each smectic layer has a bilayer structure with backbones and spacers confined in a thin disordered region between two sublayers of mesogenic segments. One of the structures which we denote as CrE* has the unusual feature of having its side chains arranged parallel to the layer normal in spite of its enantiomeric bias and twisted nature. In the second structure side chains are tilted by 34.8° with respect to the layer normal and we denote this phase as CrH*_c In both structures each sublayer contains three different orientations of orthorhombic (CrE) or monoclinic (CrH*_c) lattices which are related to one another by rotations of ± 60° about the c-axis. In both the CrH*_c and the CrE* phases, lattices in each sublayer are regularly rotated about the c-axis by 5.9° relative to those in the adjacent sublayer. The observation of a chiral CrH phase is uncommon and in this specific case the structure is unique since the rotation between adjacent layers occurs about the sidechain axis (c-axis) (CrH*_c) and not about the layer normal (c-axis) (CrH*_c). We believe the system undergoes a change in molecular organization from CrH*_c to CrE* as a result of a chemical reaction which joins a fraction of the stereocentres through covalent bonds. With increasing temperature the CrE* structure was found to transform to a special orthorhombic untwisted smectic phase in which a = 31/2b, denoted here as CrE_h. The structure then transforms to a hexatic S_B phase and finally to a S_A phase at yet higher temperatures.