Chiral Liquid Crystal Polymers Research Articles

Competition between Circularly Polarized Light and Molecular Chirality in the Assembly of Main-chain Liquid Crystalline Polymers

Abstract Polymeric systems responding to chiral information are actively pursued for applications in optoelectronics and photonics. Here we report on the diastereomeric relationship between chiral liquid crystal polymers and circularly polarized light (CPL). We synthesize a chiral copolymer incorporating photoisomerizable diazobenzene moieties as well as isosorbide-based monomers. The circular dichroism of the film can be inverted by irradiation with CPL indicating that the influence of the chiral subunits on the helicity of the cholesteric arrangement can be overruled by the action of CPL. By following the out-of-equilibrium photo-switching process over time, we demonstrate that the formation of helical ordering in the chiral liquid crystal phases is much faster by CPL irradiation than by heat.

The effect of different photoluminescent side-chain length on the phase behaviour of chiral liquid crystal polymer

ABSTRACT Fluorescent liquid crystal polymers have attracted much attention because of the combination of fluorescence, liquid crystallinity and processability. In this study, we designed and synthesised two series of photoluminescent cholesteric liquid crystal polysiloxanes, which contained cholesterol mesogens and fluorescein methyl ester with different side chain lengths. The chemical structures and liquid crystal properties of the polymers were investigated by the usual methods. The photoluminescent property were characterised by fluorescence spectroscopy. At the same time, the effects of the lengths of the fluorescent group chains on the liquid crystal and fluorescence properties of the polymers were studied. The results showed that the synthesised polymers possessing very good fluorescent and liquid crystal properties, which may has certain practical value and application prospect.

Synthesis of a polyacetylene derivative bearing aspirin with chiral charge carrier “chiralions”

The synthesis of a polyacetylene-bearing aspirin was conducted. Gas-phase iodine doping of the polymer provided evidence of chemical interaction between the polyene and iodine, which acted as an electron acceptor. The polymer in a chiral aspirin derivative shows entire helical structure with optical activity. The electronic properties of the π-conjugated chiral liquid crystal polymer blend with a helical structure were evaluated.

Influence of molecular weight on helical twisting power of oligomer chiral dopants

Chiral mesogenic monomers have been widely used in applications based on chiral liquid crystals, where polymerization is normally required to fulfill the device function. The change of molecular weight has a notable impact on the properties of the formed polymers. Herein, we systematically investigate the influence of molecular weight on the helical twisting power (HTP) of chiral oligomers when used as chiral dopants. Two series of side-chain and main-chain liquid crystal oligomers are synthesized and examined in terms of phase behavior, HTP value and dependence on temperature. The relationship between the HTP value and molecular weight of the oligomer is established, which is markedly dependent on the molecular structure. The insights obtained from the current study could help develop methods to in-situ analyze functional devices based on chiral liquid crystal polymers.

Induction of Polyacetylene to a Chiral Smectic Liquid Crystal-Chiral Direct Conversion.

The synthesis of polyacetylene-bearing pyrimidine-type three-ringed mesogenic core exhibiting smectic C (SmC) characteristics was conducted. Gas-phase iodine doping of the polymer provided evidence of chemical interaction between the polyene and iodine, which acted as an electron acceptor. The side-chain fluorine atom tilted the mesogen moiety to form SmC as a tilted liquid crystal. The addition of a small amount of chiral inducer yielded SmC* of the polymer as the chiral version of SmC. The liquid crystallinity and electronic properties of the π-conjugated chiral liquid crystal polymer with a helical structure were evaluated.

The Effect of the Applied Temperature on the Maximum Refleactive Wavelength in Chiral Liquid Crystal Polymers

The liqud crystals (LCs) monomers 4-(Undecenoic-1-yloxybenzoyloxy)-4’-cyanobenzene e M1 and 5-{4-[4-(4-undecyloxy) biphenyl] -oxycarbonyl} pentanoic acid cholesteryl ester M2 are synthesized. The liquid crystals polymer was synthesized by nematic and chiral LC monomers. The property of the LC materials are detected by POM and DSC. The bandgaps of the LC polymer are influenced by the change of temperature. The effect of temperature on the reflective wavelength is decreased from 513nm to 394nm with temperature increased. The chiral LC polymer is a one dimension photonic materials. The optical and thermal property of the CLCs polymer is controlled by the out field, and widely used for display, smart windows and chiral liquid crystal laser etc.

Modification of chiral liquid crystal polymers by charged 2D nanoplatelets towards colorful nanocomposites with tunable wetability

Chiral liquid crystal polymers (CLCPs) with spontaneous ordered structure, unique optical properties and high flexibility are promising smart materials. However, their broad application is inevitably limited by the single attribute of chiral mesophase in the cases of fabricating functional materials with multiple attributes. In this work, a novel and effective method of modifying CLCPs by charged two-dimensional (2D) zirconium phosphate (ZrP) nanoplatelets is established. ZrP nanoplatelets can be incorporated into the matrix of CLCPs by the host-guest effect. The dispersed ZrP nanoplatelets can increase the glass transition temperature due to the steric hindrance. The incorporation of ZrP nanoplatelets can increase the thermal decomposition temperature of CLCPs from 274.2 °C to 316.9 °C when the ZrP content ranging from 0 wt% to 20 wt%. The CLCP-ZrP nanocomposites exhibit typical thermochromism in the visible light region in response to temperature. The intercalation of ZrP nanoplatelets can tune the wettability of CLCPs from hydrophobicity to hydrophilicity, the contact angles are within the range from 26.25° to 110.0°. We believe the modification of CLCPs by ZrP nanoplatelets paves the way to functionalize polymer matrix by a variety of novel 2D materials, such as black phosphorus, MXenes and transition-metal dichalcogenides, and to fabricate multifunctional nanocomposites.

Regulating the modulus of a chiral liquid crystal polymer network by light.

We report a novel way to modulate the elastic modulus of azobenzene containing liquid crystal networks (LCNs) by exposure to light. The elastic modulus can cycle between different levels by controlling the illumination conditions. Exposing the polymer network to UV light near the trans absorption band of azobenzene gives a small reduction of the glass transition temperature thereby lowering the modulus. The addition of blue light addressing the cis absorption band surprisingly amplifies this effect. The continuous oscillatory effects of the trans-to-cis isomerization of the azobenzene overrule the overall net cis conversion. The influence on the chain dynamics of the network is demonstrated by dynamic mechanical thermal analysis which shows a large shift of the glass transition temperature and a modulus decrease by more than two orders of magnitude. The initial high modulus and the glassy state are recovered within a minute in the dark by switching off the light sources, despite the observation that azobenzene is still predominantly in its cis state. Based on these new findings, we are able to create a shape memory polymer LCN film at room temperature using light.

Synthesis and characterization of chiral liquid crystal polymers containing donor–acceptor group

A series of new chiral side-chain liquid crystalline polymers with electron donor–acceptor action were prepared containing chiral monomer with donor group and nematic LC monomer with acceptor group. All polymers were synthesized by graft polymerization using polymethylhydrosiloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), thermogravimetric analyses (TGA), and X-ray diffraction measurements (XRD). The chemical structures of monomers and polymers were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra (1H NMR and 13CNMR). M1 did not show liquid crystalline phase and M2 turned out nematic phase on heating and cooling cycle. Polymers P2–P7 were cholesteric phase. Cholesteric phase and low glass temperature liquid crystalline polymers have been obtained, which offered the possibility of application. Experimental results demonstrated that the glass-transition temperatures rose and isotropization temperatures decreased and the ranges of the mesophase temperature reduced with increasing the content of chiral agent. All of the obtained polymers showed high thermal stability.

Chiral liquid crystal polymers with potential ferroelectric properties: Synthesis and characterization

Abstract The synthesis and thermal properties are described of new series of chiral side chain liquid crystalline polymers containing monomeric units constituted by a biphenylyl moiety variously spaced from the hydrocarbon backbone both in length and functionality. SA and chiral Sc phases were detected in different ranges of temperature whose onset and stability are dependent on the length and parity of the polymethylene spacer.

Cholesteric mesophases

In the past few years, there have been important developments concerning the role and the use of chirality in liquid crystals. An example which is now relatively well known is the chiral smectic C* low molecular weight liquid crystal (LMWLC) which lowers the response time of displays by a factor between one hundred and one thousand [1-3]. In chiral liquid crystal polymers (cholesteric or twisted nematic and smectic C*), it is necessary to understand the relation between the chemical structure and the properties of mesophases in liquid and solid polymer. Furthermore, chirality is also found in abundance in biopolymers and may be important for life processes. Applications in industry (high modulus fibers, sensors, non linear optics...) have already been realised or are being pursued.The aim of this paper is to emphasize the polymer character of these liquid crystals. What is the influence of the molecular weight, the degree of substitution, the viscoelasticity and the existence of a glass transition? How to use the polymer character to obtain new informations on the liquid crystal state or to make new devices?This rapid overview roughly covers the following parts:(1) Formation and general properties of cholesteric mesophases: we give a rapid discussion of thermotropics and lyotropics, of the influence of degree of polymerisation, degree of substitution, concentration, temperature..., on the cholesteric-isotropic transition and on the order observed by textures or as described more quantitatively by the order parameter.(2) Optical properties: we give a brief presentation of a theoretical work concerning the pitch prediction taking into account the asymmetric term in the interaction potential and the comparison with experimental results.(3) Textures and defects which are mainly observed in these mesophases.(4) Flow properties and rheological behaviour which are fundamental for processing.(5) Blue phases near the isotropic-cholesteric transition which are discussed with emphasis on the specificity of the polymer state.It is usual to distinguish main chain and side chain liquid crystal polymers [4, 5], which may be modelled as indicated in Fig. 1.Cellulosic derivatives are good examples of main chain cholesteric polymers [6]. Cellulose is a very abundant polymer: each year, biosynthesis produces about 1011 tons of cellulose. It readily accepts grafting of substituents, thus producing derivatives like cellulose acetate of hydroxypropylcellulose.Examples of side chain liquid crystal polymers are those obtained with homo- or copolymers of polyacrilate, polymethacrylate or polysiloxane.

Chiral liquid crystal polymers. 6. Preparation and properties in solution and in bulk of optically active thermotropic copolyesters

Preparation par polycondensation en solution de (S)-propanediol-1,2 et de melange, de terephtalate de bis(carboxy-4 phenyle) lineaire, mesogene et de phtalate de bis(carboxy-4 phenyle) isomere, non mesogene ou d'isophtalate de bis(carboxy-4 phenyle)

Chiral Liquid Crystal Polymers. 5. Synthesis and Characterization of Thermotropic Polyesters of 3-O-alkylated Glycerols

Abstract The preparation is reported of a new series of chiral polyesters based on mesogenic bis(4-carboxy-phenyl) terephthalate triads and optically active or raceraic 3-O-substituted glycerols. An analysis of the properties in solution and in bulk of the prepared polymers is presented. All the investigated samples exhibit a thermotropic behavior in rather accessible temperature ranges. Cholesteric structures displaying temperature dependent reflection of visible light were evidenced in all the optically active polymers.

Chiral liquid crystal polymers, 4. Chiroptical properties of thermotropic polyesters in dilute solution

Chiral liquid crystal polymers, 4. Chiroptical properties of thermotropic polyesters in dilute solution