Effects of the cinnamoyl group on liquid crystal aligning capabilities on PCEMA surfaces

Four kinds of poly(4-methacryloyloxychalcone) (PCEMA) photo-alignment materials were synthesized. The effect of the cinnamoyl group on liquid crystal (LC) aligning capabilities and electro-optical characteristics of photo-aligned twisted nematic (TN) liquid crystal displays (LCDs) was investigated by photo-dimerization. Uniform NLC alignment by linearly polarized UV exposure at normal incidence on the PCEMA surfaces having a high density of cinnamoyl groups was observed. Also, excellent voltage-transmittance (V-T) curves for the photo-aligned TN-LCDs on the PCEMA surfaces was achieved. We find that the V-T and response time characteristics can be improved by increasing the density of cinnamoyl groups.     

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.     

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.     

Response time mechanism for a photo-aligned vertical-alignment liquid crystal display on a homeotropic alignment layer

The electro-optical characteristics of the photo-aligned vertical-alignment liquid crystal display (VA-LCD) with a non-polarized UV exposure of 45° on homeotropic polyimide (PI) surface was investigated. The domain size of the photo-aligned VA-LCD increases proportionately with the UV exposure time. The LC alignment of the photo-aligned VA-LCD is attributed to photo-dissociation of the polymer by UV exposure on the homeotropic PI surface. Good voltage-transmittance characteristics of the photo-aligned VA-LCD without negative compensation film was measured. The response time of the photo-aligned VA-LCD was slow compared with a rubbing-aligned VA-LCD; this is considered to be due to the alignment of LC molecules.     

Synthesis,self‐assembly,and formation of photo‐crosslinking‐stabilized fluorescent micelles covalently containing zinc(II)‐bis(8‐hydroxyquinoline) for ABC triblock copolymer bearing cinnamoyl and 8‐hydroxyquinoline side groups

Triblock copolymers (MPEG‐b‐PCEMA‐b‐PHQHEMA) bearing cinnamoyl and 8‐hydroxyquinoline side groups with different block length are synthesized by a two‐step reversible addition fragmentation chain transfer polymerization of cinnamoyl ethyl methacrylate (CEMA) and 2‐((8‐hydroxyquinolin‐5‐yl)methoxy)ethyl methacrylate (HQHEMA), respectively. The self‐assembly of MPEG‐b‐PCEMA‐b‐PHQHEMA in mixture of THF and ethanol is investigated by varying the ratio of THF and ethanol. Spheric micelles with diameter of 63.7 nm and polydispersity of 0.128 are obtained for MPEG₁₁₃‐b‐PCEMA₁₅‐b‐PHQHEMA₁₇ in THF/ethanol with a volume ratio (v/v) of 5/5. The PCEMA inner shell of the resulted micelles is photo‐crosslinked under UV radiation to give stabilized micelles. The complex reaction of the stabilized micelles with Zn(II) is investigated under different conditions to give zinc(II)‐bis(8‐hydroxyquinoline)(Znq₂)‐containing micelles. When the complex reaction is carried out in THF/ethanol (v/v = 5/5) or THF/toluene (v/v = 6/4) with zinc acetate, fluorescent Znq₂‐containing micelles are obtained without obvious change in diameters and morphologies. The fluorescent micelles exhibit green emission with λ_max at 520 nm. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1056–1064     

Response time mechanism for a photo-aligned vertical-alignment liquid crystal display on a homeotropic alignment layer

The electro-optical characteristics of the photo-aligned vertical-alignment liquid crystal display (VA-LCD) with a non-polarized UV exposure of 45° on homeotropic polyimide (PI) surface was investigated. The domain size of the photo-aligned VA-LCD increases proportionately with the UV exposure time. The LC alignment of the photo-aligned VA-LCD is attributed to photo-dissociation of the polymer by UV exposure on the homeotropic PI surface. Good voltage-transmittance characteristics of the photo-aligned VA-LCD without negative compensation film was measured. The response time of the photo-aligned VA-LCD was slow compared with a rubbing-aligned VA-LCD; this is considered to be due to the alignment of LC molecules.     

Acetylene-containing highly birefringent rod-type reactive liquid crystals based on 2-methylhydroquinone

New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δn) values of 0.32–0.40.     

Effects of hyperbranched prepolymers prepared from butyl acrylate and butyl methacrylate on the electro‐optical properties of polymer dispersed liquid crystal

Two hyperbranched prepolymers were synthesized via the reversible addition‐fragmentation chain transfer copolymerization of butyl acrylate or butyl methacrylate with divinyl benzene, respectively. These prepolymers were used in the photopolymerization‐induced phase separation process of preparing polymer dispersed liquid crystal (PDLC) films with no risk of gelation. The morphologies of PDLC samples were investigated. Of particular interest was that the driving voltage (V₉₀) of PDLC with high glass transition temperature (T_g) matrix was as low as 5 V, whereas the V₉₀ of PDLC with low T_g matrix was still high. An explanation for this phenomenon is the hypothesis that different interaction modes function at the interface of liquid crystal and polymer. Meanwhile, the hysteresis of the two systems was minor, which correlated with the hyperbranched structure of polymer. The on‐state transmittance (T_ON) of PDLC films enhanced because of the well matching between the refractive index of polymer and that of liquid crystal. Copyright © 2011 John Wiley & Sons, Ltd.     

Generation of pretilt angle in NLCs and EO characteristics of a photo-aligned TN-LCD with oblique non-polarized UV light irradiation on a polyimide surface

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment in cells with oblique non-polarized ultraviolet (UV) light irradiation on polyimide (PI) surfaces. It was found that monodomain alignment of the NLC is obtained with an incident angle of 70 degrees and 75 degrees on the PI surface. It is considered that this alignment may be attributed to the anisotropic dispersion force due to photo-depolymerization of polymer on PI surfaces. Also, the generated NLC pretilt angles are all about 3 degrees at an incident angle of 70 degrees and 75 degrees for 1 h irradiation. Next, we observed that the voltage-transmittance characteristics for a photo-aligned twisted nematic (TN) LCD with an incident angle of 80 degrees on a PI surface were excellent. Also, we measured that the voltage-holding-ratio (VHR) of a photo-aligned TN-LCD is about 94%; it is almost same as obtained for rubbing-aligned TN-LCDs. Finally, the slow response time of photo-aligned TN-LCDs is attributable to their weak anchoring strength.     

Encapsulation of nanomaterials using an intermediary layer cross‐linkable ABC triblock copolymer

For the preparation of core‐shell nanoparticles containing functional nanomaterials, a photo‐cross‐linkable amphiphilic ABC triblock copolymer, poly(ethylene glycol)‐b‐poly(2‐cinnamoyloxyethyl methacrylate)‐b‐poly(methyl methacrylate) (PEG‐PCEMA‐PMMA), was synthesized. This triblock copolymer was then used to encapsulate Au nanoparticles or pyrene. The triblock copolymer of PEG‐b‐poly(2‐hydroxyethyl methacrylate)‐b‐PMMA (PEG‐PHEMA‐PMMA) (M_n = 15,800 g/mol, M_w/M_n = 1.58) was first synthesized by activators generated by electron transfer atom transfer radical polymerization. Its middle block was then functionalized with cinnamoyl chloride. The degrees of polymerization of the PEG, PHEMA, and PMMA blocks were 45, 13, and 98, respectively. PMMA‐tethered Au nanoparticles (with an average diameter of 3.0 nm) or pyrene was successfully encapsulated within the PEG‐PCEMA‐PMMA micelles. The intermediary layers of the micelles were then cross‐linked by UV irradiation. The spherical structures of the PEG‐PCEMA‐PMMA micelles containing Au nanoparticles or pyrene were not changed by the photo‐cross‐linking process and they showed excellent colloidal stability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4963–4970, 2009     

Syntheses of new diluents for medium birefringence liquid crystals materials

New liquid crystals of 3HEHV ((4-trans-propyl-cyclohexyl-1), (4?-vinyl-cyclohexyl-1?)-ethane-1,2) and 3HB2V ((4-trans-propyl-cyclohexyl-1), (4-butenyl-3,4)-benzene) were synthesised and evaluated as the diluents for medium birefringence liquid crystal mixtures. The procedures transferring cis-isomers into trans-isomers of the cyclohexane were described. The results showed that both 3HEHV and 3HB2V decrease the crystallisation temperature and the viscosities by doping them with the medium birefringence mixtures in a fraction of 15%. The characteristics of the structures are correlated with the properties of the mixtures.     

Diblock copolymer nanostructures

Polystyrene-block-poly(2-cinnamoylethyl methacrylate) (PS-b-PCEMA) and poly(acrylic acid)-block-poly(2-cinnamoylethyl methacrylate) (PAA-b-PCEMA) were synthesized. These polymers formed micelles with PCEMA as the core in solvents poor for the PCEMA block but good for the other blocks. When the PS block was much longer than the PCEMA block, star micelles were prepared. The PCEMA cores of these micelles were then photo-crosslinked to yield PS star polymers. Nanospheres of PCEMA were obtained by photolyzing crew-cut micelles of PAA-b-PCEMA, in which the water-soluble PAA block was much shorter than the water-insoluble PCEMA block. PS-b-PCEMA self-assembled at silica and their THF/cyclopentane micellar solution interfaces to form diblock monolayers called polymer brushes, in which the insoluble PCEMA block spread like a melt on the silica surface and the chains of the soluble PS block stretched into the solution phase like bristles of a brush. By tuning the relative composition, PCEMA in bulk formed cylindrical micro-domains dispersed in the continuous PS matrix. Irradiation of the PS-b-PCEMA brushes enabled our preparation of crosslinked PS-b-PCEMA monolayers. Nanofibers were prepared by dissolving in THF the irradiated PS-b-PCEMA films with crosslinked cylindrical PCEMA micro-domains.     

Liquid crystal alignment and pretilt angle generation on a photopolymer layer based on N-(phenyl)maleimide

A photopolymer based on N-(phenyl)maleimide was synthesized and the liquid crystal (LC) alignment effects of the photopolymer layer on homeotropic alignment were studied. Good LC alignment with UV exposure of PMI5CA (N-(phenyl)maleimide with a 5-carbon chain cinnamoyl group) was obtained. However, defective LC alignment was observed for PMI3CA (N-(phenyl)maleimide with a 3-carbon chain cinnamoyl group) and PMIF (N-(phenyl)maleimide including a fluoro-cinnamoyl group). Good LC alignment with UV exposure on the PMI5CA surface was observed with annealing temperature up to 150°C. It seems that the LC aligning ability of the photopolymer layers based on N-(phenyl)maleimide depends on the side chain length of the photopolymer.     

SYNTHESIS AND MESOMORPHIC PROPERTIES OF PALLADIUM CHELATES OF LIQUID CRYSTAL POLYSILOXANE WITH β-DIKETONE-BASED SIDE CHAINS

A new type of palladium chelate of β-diketone-based side chain liquid crystal polysiloxane (Pd-DKLCP) has been synthesized by chelation reaction of palladium dichloride with polymeric ligand, β-diketone polysiloxane (DKLCP), using THF as solvent at R.T.. The Pd-chelation results in greatly increasing the phase transition temperature T_K and the enthalpy change △H_K from crystal to liquid crystal state and making the temperature range of LC state △T(△T=T_(Cl)-T_K) widened. All these chelates Pd-DKLCP's do not show T_(Cl) until decomposition at 205℃. It is noteworthy that the Pd-chelation can exert more positive effect on the mesomorphic behaviour of the polymer ligand than the counterpart Cu-DKLCP does. It is probable due to the bigger size of disc-like mesogen formed from β-diketone and Pd~(+2) ion with 4d orbital.     

A novel liquid crystals photoalignment layer-by-layer self-assembled film fabricated with long side-chain cinnamate polyelectrolyte

A novel photoalignment film for liquid crystals (LC) was prepared based on layer-by-layer self-assembly of photosensitive long side-chain cinnamate polyelectrolyte. A series of self-assembled films with different methylene spacer groups was prepared and used as alignment film. The film became anisotropic, and could induce uniform alignment of LC after irradiation by linearly polarised ultraviolet light (LPUVL). The effects of spacer chain lengths of the cinnamoyl polycations on the structure and photoalignment properties of the self-assembled film were studied. The polycation films with longer spacer chain obtained a larger dichroic ratio after LPUVL irradiation. The contrast ratio (T _max/T _min) of the LC cell increased with spacer chain length increase. However, it was found that the thermal stability of PSS/PACPYn films decreased with increasing chain length of polycation.     

Effects of prepolymer structure in holographic polymer dispersed liquid crystal

Three different types of polyols—poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and poly(tetramethylene glycol)—with different molecular weights (M_n) were incorporated into the prepolymer structure, and the effects were examined with regard to the morphology and performance of holographic polymer dispersed liquid crystal. Among them, PEG showing the lowest glass transition temperature (T_g) exhibited the lowest threshold voltage (V_th), lowest operating voltage (V_op), and lowest diffraction efficiency with slow grating formation owing to its high viscosity of prepolymer mixture. The T_g decreased with increasing M_n because of the decreased crosslink density and hydrogen bonding, which reduced the anchoring strength, V_th and V_op. PPG400 gave V_th and V_op of approximately 7 and 24 V, respectively, with a contrast ratio of approximately 12. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Functional polymethacrylates as bacteriostatic polymers

Two copolymers, P(PCEMA-co-MMA) and P(t-BMA-block-PCEMA), were prepared via ATRP using 2-(phenoxycarbonyloxy)ethyl methacrylate (PCEMA) as reactive monomer and methyl methacrylate (MMA) or tert-butyl methacrylate (t-BMA) as co-monomers. Alternatively phenoxycarbonyloxy decorated polymethacrylates were obtained via polymer analogous reaction: P(HEMA) was reacted with phenyl chloroformate to yield P(PCEMA). The highly reactive phenoxycarbonyloxy groups were used for polymer analogous reactions with nucleophiles to obtain polymers with ionic/hydrophilic and hydrophobic side groups. Different amines with long alkyl chains or tertiary amine groups were reacted with phenoxycarbonyloxy decorated polymers and subsequently reacted with methyl iodide to obtain amphipathic polymers with bacteriostatic properties.     

Influence of functional groups on the self-assembly of liquid crystals

Functional groups in the molecule play an important role in the molecular o rganization process.To reveal the influence of functional groups on the self-assembly at interface,herein,the self-assembly structures of three liquid crystal molecules,which only differ in the functional groups,are explicitly characterized by using scanning tunneling microscopy(STM).The high-resolution STM images demonstrate the difference between the supramolecular assembly structures of three liquid crystal molecules,which attribute to the hydrogen bonding interaction and π-π stacking interaction between different functional groups.The density functional theory(DFT) results also confirm the influence of these functional groups on the self-assemblies.The effort on the self-assembly of liquid crystal molecules at interface could enhance the understanding of the supramolecular assembly mechanism and benefit the further application of liquid crystals.     

Influence of the smectic A-nematic transitional order on the formation of the smectic phases of 4-n-hexyloxybenzylidene-4′-n-butyIaniline and 4-n-butyloxybenzylidene-4′-n-octyIaniline from an electrically deformed nematic phase

Abstract

The crucial role of the smectic A-nematic transitional order for the formation of the smectic A, B and G phases from an electrically deformed nematic phase of the liquid crystal 4-n-hexyloxy-benzylidene-4′-n-butylaniline (6O.4) with a typical smectic A-nematic first order transition and the formation of the smectic A and B phases from an electrically deformed nematic phase of the liquid crystal (4-n-butyloxy-benzylidene-4′-n-octylaniline (40.8) with a smectic A-nematic second order transition has been demonstrated. The nematic phase was deformed by an AC voltage of 2U,_th 5U _th and 10U _th, where U _th is the threshold voltage which causes the appearance of the Fréedericksz transition in the homeotropic nematic layer. The smectic textures have been observed on free cooling of the nematic phase or after the use of an oven. The smectic A phase of the liquid crystal 60.4 was observed with the formation of a clear smectic A-nematic phase boundary while the smectic A phase of the liquid crystal 40.8 has been formed from intermediate pretransitional stripes, observed by Cladis and Torza [1]. The homeotropic anchoring of the direction was crucial for the formation of the smectic phases of the liquid crystal 40.8 but not significant for the liquid crystal 60.4.     

Effect of carbon nanotubes on phase transitions of nematic liquid crystals

Phase diagrams of multi‐wall carbon nanotube (MWNT)/nematic liquid crystal (E7) and buckminsterfullerene (C₆₀‐I _h)/nematic liquid crystal (E7) binary systems have been investigated by means of polarizing optical microscopy and differential scanning calorimetry. It was found that the isotropic–nematic phase transition temperature (T _NI) of the liquid crystal component was enhanced by the incorporation of MWNT within a small composition gap. A chimney‐type phase diagram can be identified in the MWNT/E7 mixture over a narrow range of ～0.1–0.2% MWNT concentration. Upon substituting the nanotubes with isotropic fillers such as fullerene, the (C₆₀‐I _h)/E7 blend showed no discernible change of T _NI in the same concentration range of the chimney of the MWNT/E7 mixture, suggesting a significant contribution of anisotropy (or the aspect ratio) of the nanotubes to the entropy of the system containing liquid crystal molecules. This enhanced T _NI phenomenon may be attributed to anisotropic alignment of liquid crystal molecules along the carbon nanotube bundles.