Thermotropic and optical behaviour of new PDLC systems based on a polysulfone matrix and a cyanoazomethine liquid crystal

The thermotropic and optical characterisations of a novel polymer dispersed liquid crystal (PDLC) system based on polysulfone UDEL P-1700 as polymer matrix and a low molecular weight liquid crystal compound containing a mesogenic azomethine core and a cyano-substituent were investigated. The PDLC samples were prepared by solvent-induced phase separation (SIPS) and thermally induced phase separation (TIPS) methods using various compositions in the two components. Information on the morphology and phase structure was obtained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. PDLC systems with well-defined droplets were obtained for the composite with medium content of liquid crystal compound. The optical characterisation of these materials was performed by analysing their UV–visible absorption and photoluminescence emission as a function of the liquid crystal aggregation degree.     

Protein triggered ordering transitions in poly (L-lysine)-coated liquid crystal emulsion droplets

Here, we report a simple and label-free methodology for real-time monitoring of adsorption of proteins such as bovine serum albumin (BSA), concanavalin A (ConA) (a lectin) and cathepsin D (CathD) (a tumour marker) on micrometer-sized poly (L-lysine) (PLL) functionalised liquid crystal (LC) droplets dispersed in aqueous phases. Earlier, we had demonstrated that PLL, a positively charged natural peptide, can induce homeotropic ordering of LCs at LC-aqueous interface, and thus PLL-adsorbed LC droplets showed radial director configuration. Herein, it was observed that subsequent non-specific adsorption of anionic proteins such as BSA, ConA and CathD can trigger a quick transition in director configuration of PLL-LC droplets (primarily dominated by electrostatic interactions) to pre-radial or bipolar, thus acting as a simple optical probe for detection of these proteins up to μg/mL of concentrations. Further, the detection limits for these proteins are found to vary (BSA<ConA<CathD) which follow the similar order as their anionic charges, thus suggesting the role of different binding affinities of protein-PLL in realising the director configuration of LC droplets. Overall, this study offers new pathways utilising ordering transition in LC droplets which will strengthen the principles to recognise biomolecular interactions for various interfacial and sensing applications.     

Double emulsion droplets as microreactors for synthesis of magnetic macroporous polymer beads

An easy method is presented to fabricate monodisperse magnetic macroporous polymer beads（MMPBs）. Waterin-oil high internal phase emulsion（HIPE） is prepared by emulsifying aqueous iron ions solution in an oil phase containing monomers. The HIPE is introduced into a simple microfluidic device to fabricate monodisperse（water-in-oil）-in-water double emulsion droplets. The droplets serve as microreactors to synthesize Fe3O4 nanoparticles and are on-line polymerized to form MMPBs. The prepared MMPBs display uniform size, interconnected porous structure, superparamagnetic behavior and uniform distribution of Fe3O4 in polymer matrix. The MMPBs are characterized by scanning electron microscopy（SEM）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometry（VSM）. We believe that this method is a universal technique in preparing macroporous nanocomposite beads.     

Size control of phase‐separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Behavior of a nematic liquid near a grafted solid surface

We discuss the nematic order parameter and the polymer concentration profile for a solid surface carrying grafted chains. Different regimes are found, depending upon the polymer chain length and the grafting density. These ideas are compared with experimental results obtained with polystyrene in the presence of pentylcyanobiphenyl.     

Ternary hydrogen halide/base/benzene mixtures: A new generation of liquid clathrates

Liquid clathrates have been prepared via contact of excess hydrogen halide (chloride or bromide) with benzene solutions of various simple organic nitrogen containing bases. The liquid clathrates or solutions so formed have been characterized via¹H NMR and shown to be, as expected, ternary mixtures of hydrogen halide, benzene and salt.     

Effects of the fluorinated liquid crystal molecules on the electro-optical properties of polymer dispersed liquid crystal films

The different fluorinated liquid crystal (LC) molecules doped to E8 were used as LC component to prepare polymer dispersed liquid crystal (PDLC) films. The mass fraction of the LC mixture is fixed 50.0 wt%. Results indicate that doping 8.0 wt% fluorinated LC molecule ME3CP to E8 significantly reduced the driving voltage of the PDLC films, and the driving voltage reduced with the rise of mass fraction of ME3CP. Besides, the terminal flexible chain length of the fluorinated LC molecule influenced the LC mixture properties based on E8, such as the dielectric anisotropy, birefringence and viscosity of the LC mixture, and the morphology and the electro-optical properties of PDLC films were controlled not only by the physical properties of the LC mixture, but also by the terminal flexible chain length of the fluorinated LC molecule .     

Automation of static and dynamic non-dispersive liquid phase microextraction. Part 1: Approaches based on extractant drop-, plug-, film- and microflow-formation

Simplicity, effectiveness, swiftness, and environmental friendliness – these are the typical requirements for the state of the art development of green analytical techniques. Liquid phase microextraction (LPME) stands for a family of elegant sample pretreatment and analyte preconcentration techniques preserving these principles in numerous applications. By using only fractions of solvent and sample compared to classical liquid–liquid extraction, the extraction kinetics, the preconcentration factor, and the cost efficiency can be increased. Moreover, significant improvements can be made by automation, which is still a hot topic in analytical chemistry. This review surveys comprehensively and in two parts the developments of automation of non-dispersive LPME methodologies performed in static and dynamic modes. Their advantages and limitations and the reported analytical performances are discussed and put into perspective with the corresponding manual procedures. The automation strategies, techniques, and their operation advantages as well as their potentials are further described and discussed.     

Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal

Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4?-n-hexylbiphenyl (6CB) or 4-cyano-4?-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.     

CPI induction of liquid crystal behaviour in triphenylenes with a mixture of hydrophobic and hydrophilic side chains

2,3,6,7,10,11-Hexasubstituted triphenylenes have been synthesized that contain a mixture of hydrophobic (C₆H₁₃O) and hydrophilic (CH₃OCH₂CH₂OCH₂CH₂O) side chains. At one extreme HAT6 (1a) (six hydrophobic chains) shows thermotropic behaviour and at the other TP6EO2M (1e) (six hydrophilic chains) shows lyotropic behaviour. Of the triphenylenes with a mixture of hydrophobic and hydrophilic side chains, only the triphenylene with one hydrophilic side chain and five hydrophobic side chains (1b) gives a thermotropic columnar phase. None of the others show liquid crystal behaviour. However, all of these triphenylenes form binary 1:1 compounds when mixed with PDQ9 (2a) and with PTP9 (2b). These CPI (complimentary polytopic interaction) stabilized compounds give thermotropic hexagonal columnar phases over wide temperature ranges.     

Spreading and infiltration of inkjet-printed polymer solution droplets on a porous substrate

Simultaneous spreading and infiltration of inkjet-printed droplets has been studied. Small (54- and 63-microm diameter) droplets of an aqueous polymer solution (2.4 vol% polyacrylic acid, PAA, MW 60,000) were deposited on high green density porous ceramic beds, and the wetting-induced spreading and infiltration of the droplets were characterized. The time scales for spreading and infiltration were comparable (approximately milliseconds), resulting in interruption of the spreading prior to completion by infiltration of the liquid into the powder bed, a situation that has received little treatment in the literature. The infiltration time was varied by changing the pore size (via particle size) in the powder bed, and it was confirmed that slower infiltration resulted in greater spreading of the liquid. The spreading and infiltration of the droplet were modeled to examine the coupling between the two processes and allow prediction of the maximum extension of the droplet as a function of the powder bed particle size. The liquid spreading was found to follow r(t)=a(b+t)(n) behavior, and the effect of particle size on infiltration time was used to predict the point at which spreading ceases due to infiltration for various particle sizes.     

Crystallization of condensation droplets on a liquid surface

Highly ordered microporous two-dimensional membranes have been obtained from polymer solutions (Widawski et al. (1994) Nature 369: 397–399). Recently, a mechanism for the formation of such membranes was proposed, involving water vapour condensation (induced by the rapid evaporation of the volatile solvent) onto the surface of solutions and the formation of floating water droplets. Unfortunately, the droplets growth process was not observed, and consequently only qualitative information was reported. In the present paper, results of light-scattering experiments with this system are reported. The formation of water droplets growing at the surface of the solution has been observed and the evolution with time of the mean droplet radius has been found to be described by a power law with an exponent of 1/3, proving that no coalescence processes occur. This particular behaviour is attributed to the precipitation of the polymer at the water/solution interface and to the formation of a mechanically resistant polymer layer encapsulating each droplet. In this way, water droplets behave like solid particles, allowing compact sheets to be formed. The presence of important surface currents is believed to promote the formation of “polycrystal” and “monocrystal” patterns. Received: 4 January 1999 Accepted in revised form: 15 February 1999     

Spreading and sorption of droplets on layered porous substrates

In this paper spreading and sorption of a droplet on an anisotropic, layered porous substrate are investigated numerically. Flow in the saturated part of the porous material is governed by Darcy's law, assuming a sharp wetting front separating the saturated regions from the dry regions. Numerical results are presented for spreading and sorption of droplets in their dependence on the material and process parameters for axisymmetric configurations. Limiting cases of sorption into infinitely thick and very thin porous layers are considered. For an analytical sorption model for thin substrates fed by an infinite reservoir a correction term taking into account the flow resistance in the inlet region is derived and the consistence of the modified model with numerical and experimental results is shown. For two-layer substrates, numerical results on the influence of the layer permeabilities on the sorption kinetics are presented.     

Synthesis and properties of reactive liquid crystal monomers and side-chain liquid crystalline polymers

Two nematic liquid crystal (LC) monomers containing double bonds in the side chain were designed and synthesised. Length of the side groups varied from 1 to 2 methylene units. The side-chain polymers were synthesised by hydrosilylation reaction. The molecular structures of the intermediates and the LC monomers were characterised by Fourier transform infrared, elemental analysis and nuclear magnetic resonance spectroscopy. The thermal phase behaviour of the monomers and polymers were investigated by differential scanning calorimetry and polar optical microscopy coupled with hot stage. The LC monomers showed only one nematic mesophase in the cooling process. And, the two polymers exhibit an enantiotroppic nematic mesophase either in the heating or in the cooling process.     

Thermal transition of a wholly aromatic thermotropic liquid crystalline copolyester

A copolyester was prepared from p-hydroxybenzoic acid (HBA), 2,6-naphthalene dicaboxylic acid (NDA), and hydroquinone (HQ). Thermal transition behavior and the crystal structure of this copolyester were investigated by using polarized light microscopy (PLM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) after annealing at solid-phase polymerization conditions. A glass transition or newly ordered structure in the 270–290°C range was observed on annealing at 260°C, which increased with annealing time, attributed to mobility and reactive rearrangement in amorphous regions. Broad and unclear WAXD profiles and multimelting behaviors were found on annealing at 280°C, and explained by hexagonal and orthorhombic lattice formation and transformation. A large increase in melting temperature was observed only on annealing at a temperature (320°C) near the crystal–nematic transition, suggesting annealing temperatures near the melting point are required for sufficient mobility to afford crystalline rearrangement via transesterification. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3763–3769, 1999     

Curing of liquid crystalline epoxy resins with a biguanide

This work extends the authors' investigations on liquid crystalline epoxy resins prepared from diglycidyl ether of 4,4′-dihydroxybiphenyl (DGE-DHBP) and aliphatic dicarboxylic compounds (ADC) or difunctional aromatic compounds. Syntheses and properties of these liquid crystalline epoxy resins are described elsewhere. In this paper a study on the curing reaction of the above mentioned liquid crystalline epoxy resins is presented. Ortho-tolylbiguanide was applied as the curing agent. The curing reactions were investigated by differential scanning calorimetry, microscopic observations and IR spectroscopy. Depending upon the temperature program of curing, it was possible to obtain polymeric networks with liquid crystalline order. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2739–2745, 1997     

An electrically light-transmittance-switchable film with a low driving voltage based on liquid crystal/polymer composites

ABSTRACT

As a typical class of electrically light-transmittance-switchable (ELTS) composites materials, polymer dispersed liquid crystal (PDLC) films have been widely used in displays, smart windows, light shutters, etc. However, the commercialised PDLC film still requires a comparatively high voltage to maintain its transparent state, leading to huge power consumption and even a potential safety risk. In this regard, we proposed a ‘heat followed UV’ stepwise polymerisation strategy for preparing a kind of ELTS film with a low driving voltage (~20.7 V) through constructing a coexistent system of polymer dispersed and polymer stabilised liquid crystal (PD&SLC). In this new PD&SLC system, vertically orientated polymer networks were formed within LC domains to induce the vertical alignment of LC, thereby reducing the driving voltage. Also, the as-made PD&SLC film exhibited good flexibility due to the high content of polymer. Moreover, the effects of the liquid crystalline polymerisable monomers content on the polymer morphologies as well as the electro-optical properties of the as-made PD&SLC films were elaborately investigated.     

Synthesis of a novel star liquid crystal polymer using trifunctional initiator via atom transfer radical polymerization

In this paper, two types of three-arm star mesogen-jacketed crystal polymers (MJLCPs) with different core (that is hard core and soft core) were synthesized by 2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), which was initiated by two different trifunctional initiators 1,3,5-(2′-bromo-2′-methylpropionato)benzene (I_a) and 1,1,1-tris(2-bromoisobutyryloxymethyl)propane (I_b), respectively. Characterization of these polymers by ¹H NMR and GPC clearly supported the formation of a three-arm star-shaped PMPCS. The resulting three-arm star PMPCS possessed narrow molecular weight distribution, and its molecular weight (M_n,NMR) agreed well with the theoretical value, which reveals the quantitative initiation efficiency. The liquid-crystalline behaviors of the two types of three-arm star polymer with different structure were also investigated by differential scanning calorimeter (DSC) and polarized optical microscope (POM). We found that the liquid-crystalline behavior was incorrelated with structure of core but correlated with the length of three-arm star polymer arm. Only each arm of the three-arm star-shaped polymers with a M_n,GPC beyond 0.90 × 10⁴ g/mol could form a liquid crystalline phase,which was found to be stable up to the decomposition temperature of these tri-arm MJLCPs.     

Influence of molecular weight on liquid crystalline behavior of linear and star mesogen‐jacketed liquid crystal polymers

A series of novel multi‐armed (di‐, tri‐ and tetra‐armed) mesogen‐jacketed liquid crystal polymers (MJLCPs) were synthesized by atom transfer radical polymerization (ATRP) of {2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}(MPCS) using di‐, tri‐ and tetrafunctional initiator, respectively. The results show that the number average molecular weight (M_n,GPC) was increased versus monomer conversion, and the polydispersities were quite narrow (<1.19), which is the characteristic of controlled polymerization. The chemical structures of these multi‐armed mesogen‐jacketed liquid crystal polymers were confirmed by ¹H NMR. The liquid crystalline behavior of these multi‐armed MJLCPs with arms ranging from two to four was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide‐angle X‐ray diffraction (WAXD). It was found that liquid crystalline phases appeared simply when the number molecular weights (M_n,GPC) of these multi‐armed MJLCPs was higher than a certain critical values, that is, M_n,GPC > 1.87 × 10⁴ g/mol, 1.84 × 10⁴ g/mol, 2.69 × 10⁴ and 3.68 × 10⁴ g/mol, which were initiated by coil difunctional initiator, hard difunctional initiator, trifunctional initiator and tetrafunctional initiator, respectively. All the liquid crystalline phase was found to be stable up to the decomposition temperature of these multi‐armed MJLCPs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3232–3244, 2005