Molecular Filtration of Hydrocarbon Isomers Through Polymer/[Liquid Crystal] Composite Membranes

Ultrathin membranes of a polymer/(liquid crystal) mixture were prepared by spreading a single drop of a casting solution on the water surface. The thickness and the aggregation state of the water-cast membrane can be controlled by the kind of solvent and the concentration of the solution. In the case of a liquid crystalline state above the crystal-nematic phase transition temperature, T _KN, the polymer (liquid crystal) composite membrane follows Henry's law for the sorption isotherm of hydrocarbon gases and, also, Fickian sorption for the sorption-desorption kinetics. These results indicate that hydrocarbon gases permeate through a homogeneous medium composed of liquid crystalline molecules. Therefore, the permeability coefficients of hydrocarbon gases can be controlled by the dimensions of the channels through which the gas molecules diffuse. The channel for diffusion is generated by thermal or fluctuating molecular motion which opens up the intermolecular distance between liquid crystalline molecules. In the case of a self-supported liquid crystalline membrane, the channel dimension can be controlled in the range of several Å by both the intermolecular distance and the degree of thermal molecular motion of the liquid crystalline molecules. Separation of hydrocarbon isomers was investigated by use of composite membranes composed of a polymer matrix and self-supported liquid crystalline molecules.     

Morphology control of liquid crystalline composite gels based on molecular self-assembling kinetics

Liquid crystalline composite gels consisting of a low molecular mass gelator and a low molecular mass liquid crystal were prepared by two types of gelation method (continuous cooling and isothermal gelating), which provide different molecular self-assembling kinetics of the low molecular mass gelator as gelation proceeds. Optical microscopy and atomic force microscopy revealed that numerous fine strands of the one-dimensionally assembled low molecular mass gelators were formed in the composite gels for both the continuous cooling method and the isothermal gelating method. However, the thinner strands were more homogeneously dispersed in the isothermal gelation product at an appropriate temperature, than in the continuous cooling process. This difference in dispersion state of the strands was shown (by polarizing optical microscopy) to have a significant influence on the molecular alignment of the low molecular mass liquid crystal in the liquid crystalline composite gel. The electro-optical response and light scattering–transmitting switching, of the liquid crystalline composite gel in an applied electric field was extremely dependent on the morphology of the gelators. High contrast light switching was achieved for the composite prepared by isothermal gelation. The response time of electro-optical switching was less than 100?µs under 30?V_rms.     

Gas permeability of combined membrane systems with mobile liquid carrier

Gas transfer in a membrane system called a selective membrane valve (SMV) is studied. The SMV is a system consisting of two mobile gas phases, one mobile liquid phase, and two membranes acting as interfaces between gas and liquid. Such a membrane system has supplementary variable parameters and is designated for the separation of multicomponent gas mixtures. System permeability for individual gases (CO₂, O₂, and H₂) and its dependence on a flow rate of a liquid phase are studied. Time dependences of the non-steady state transfer of CO₂ through the immobile layer of chemisorbent (aqueous K₂CO₃ solution) at its different concentrations are studied for the first time. Two theoretical models are developed: the model of gas transfer through a selective membrane valve system with a mobile liquid absorbent (in the absence of chemical interaction) and the model of a non-steady-state transfer of CO₂ through the immobile layer of aqueous potassium carbonate solution. The first model makes it possible to determine gas-to-liquid diffusion coefficients; the second model permits us to plot kinetic permeability curves and to calculate system permeability with allowance for the CO₂ transfer accompanied by reversible chemical reaction with the carrier. The model dependences agree well with the experimental data.     

Morphology control of liquid crystalline composite gels based on molecular self-assembling kinetics

Liquid crystalline composite gels consisting of a low molecular mass gelator and a low molecular mass liquid crystal were prepared by two types of gelation method (continuous cooling and isothermal gelating), which provide different molecular self-assembling kinetics of the low molecular mass gelator as gelation proceeds. Optical microscopy and atomic force microscopy revealed that numerous fine strands of the one-dimensionally assembled low molecular mass gelators were formed in the composite gels for both the continuous cooling method and the isothermal gelating method. However, the thinner strands were more homogeneously dispersed in the isothermal gelation product at an appropriate temperature, than in the continuous cooling process. This difference in dispersion state of the strands was shown (by polarizing optical microscopy) to have a significant influence on the molecular alignment of the low molecular mass liquid crystal in the liquid crystalline composite gel. The electro-optical response and light scattering-transmitting switching, of the liquid crystalline composite gel in an applied electric field was extremely dependent on the morphology of the gelators. High contrast light switching was achieved for the composite prepared by isothermal gelation. The response time of electro-optical switching was less than 100 µs under 30 V_rms.     

The role of swelling,amorphous vs. crystalline content,charge density,and applied stress on the transport properties of polymeric films

Previously reported results on the transport behavior of crosslinked collagen membranes are reviewed and discussed. Under isoelectric conditions, alteration of the degree of swelling and of the state of the membrane are induced by changing salt type and concentration. The filtration coefficient L_p increases when swelling is increased in the amorphous state, decreases when swelling is increased in the crystalline state, and increases during the crystal—amorphous transition. Under non-isoelectric conditions (low pH, low ionic strength), L_p and swelling have the same trend in the amorphous state while they have opposite trends in the crystalline state. The trend of the reflection coefficient σ as a function of pH (a maximum is exhibited at pH ～ 3) is quantitatively explained on the basis of the competition between swelling and fixed charge density (the former includes a contribution due to the charge-induced phase transition at pH ～ 2, in addition to the usual Donnan contribution). The permeability to THO, ω_T, increases with increasing strain on the amorphous membrane and then goes through a maximum and a minimum when a stress-induced phase transition occurs. The relationship between frictional coefficients derived from irreversible thermodynamics and polymer-salt-water interactions deduced from equilibrium thermodynamics is pointed out.     

Synthesis and characterisation of biodegradable liquid crystal elastomer with the property of shape recovery

Novel shape recovery biodegradable liquid crystal (LC) elastomer is reported here for the first time. The method of synthesis of the shape memory biodegradable LC elastomer has been explored. During the reaction, the LC molecules are added to form LC polymers, and then cross-linking agent is added to form a cross-linked LC elastomer. The LC elastomer in this work is hydrophilic. In vitro degradation of the LC elastomer films in a buffer of pH 7.4 at 37°C shows that the LC elastomer has good degradability. The biodegradable LC elastomer exhibits liquid crystalline behaviour and has shape memory ability. Its shape memory and actuating properties also have been studied. The reversible transition from liquid crystalline phase to isotropic phase is utilised as the switching mechanism for these stimuli-responsive materials. When reheating the LC elastomer to 120°C, the shape will recover.     

Synthesis of an Azobenzene-containing Main-chain Crystalline Polymer and Photodeformation Behaviors of Its Supramolecular Hydrogen-bonded Fibers

The synthesis of a new azobenzene(azo)-containing main-chain crystalline polymer with reactive secondary amino groups in its backbone and photodeformation behaviors of its supramolecular hydrogen-bonded fibers are described. This main-chain azo polymer(namely Azo-MP6) was prepared via first the synthesis of a diacrylate-type azo monomer and its subsequent Michael addition copolymerization with trans-1,4-cyclohexanediamine under a mild reaction condition. Azo-MP6 was found to have a linear main-chain chemical structure instead of a branched one, as verified by comparing its ~1H-NMR spectrum with that of the azo polymer prepared via the polymer analogous reaction of AzoMP6 with acetic anhydride. The thermal stability, phase transition behavior, and photoresponsivity of Azo-MP6 were characterized with TGA,DSC, POM, XRD, and UV-Vis spectroscopy. The experimental results revealed that it had good thermal stability, low glass transition temperature,broad crystalline phase temperature range, and highly reversible photoresponsivity. Physically crosslinked supramolecular hydrogen-bonded fibers with good mechanical properties and a high alignment order of azo mesogens were readily fabricated from Azo-MP6 by using the simple melt spinning method, and they could show "reversible" photoinduced bending under the same UV light irradiation and good anti-fatigue properties.     

“Self-Lockable” Liquid Crystalline Diels–Alder Dynamic Network Actuators with Room Temperature Programmability and Solution Reprocessability

Novel main-chain liquid crystalline Diels—Alder dynamic networks (LCDANs) were prepared that exhibit unprecedented ease for actuator programming and reprocessing compared to existing liquid crystalline network (LCN) systems. Following cooling from 125 °C, LCDANs are deformed with aligned mesogens self-locked at room temperature by slowly formed Diels–Alder (DA) bonds, which allows for the formation of solid 3D actuators capable of reversible shape change, and strip walker and wheel-capable light-driven locomotion upon either thermally or optically induced order–disorder phase transition. Any actuator can readily be erased at 125 °C and reprogrammed into a new one under ambient conditions. Moreover, LCDANs can be processed directly from melt (for example, fiber drawing) and from solution (for example, casting tubular actuators), which cannot be achieved with LCNs using exchangeable covalent bonds. The combined attributes of LCDANs offer significant progress toward developing easily programmable/processable LCN actuators.     

Breathing Pores on Command: Redox‐Responsive Spongy Membranes from Poly(ferrocenylsilane)s

Redox‐responsive porous membranes can be readily formed by electrostatic complexation between redox active poly(ferrocenylsilane) PFS‐based poly(ionic liquid)s and organic acids. Redox‐induced changes on this membrane demonstrated reversible switching between more open and more closed porous structures. By taking advantage of the structure changes in the oxidized and reduced states, the porous membrane exhibits reversible permeability control and shows great potential in gated filtration, catalysis, and controlled release.     

Gas permeability and stability of poly(1-trimethylsilyl-1-propyne-co-1-phenyl-1-propyne) membranes

A significant reduction in the gas permeability of the poly(1-trimethylsilyl-1-propyne) (PMSP) membrane was investigated in terms of the membrane thickness and the storage environment. The effects of physical aging were observed with thinner membranes and under vacuum conditions compared with storage in air. The decrease in the permeability coefficient was dependent on the decrease in the hole saturation constant of Langmuir adsorption (C'_H), which is related to the volume of the microvoids. Physical aging in the PMSP membrane affected not only the glassy domain but also the rubbery one. To stabilize the permeability of the PMSP membrane, a poly(1-trimethylsilyl-1-propyne-co-1-phenyl-1-propyne) [poly(TMSP-co-PP)] membrane was prepared. Poly(TMSP-co-PP) has the same unit of poly(1-phenyl-1-propyne), which membrane has stable permeability. The poly(TMSP-co-PP) with less than 20 mol % PP content was estimated to be a random copolymer based on theoretical gas permeation analysis. In the poly(TMSP-co-PP) membrane, the relation between the PP content and C'_H was similar to the relation between the PP content and the gas permeability. The stability of the permeability was dependent on the PP content. The poly(TMSP-co-PP) membrane containing 10 mol % PP had both high permeability and good stability under some of the aging conditions performed in this work. © 1995 John Wiley & Sons, Inc.     

Gas permeation properties of blend and copolymer membranes composed of 1-trimethylsilyl-1-propyne and 1-phenyl-1-propyne structures

The poly(1-trimethylsilyl-1-propyne) (PMSP) has the potential to be an important membrane gas separation material due to the fact that it has the highest gas permeability of all polymeric membranes. One problem with PMSP is a decrease in the gas permeability with age. In order to understand the aging processes, we studied the change in free volume and the molecular motions of the PMSP and its membranes modified with 1-phenyl-1-propyne (PP) structures; that is, a copolymer and a blend of PMSP and PPP. During aging, the unrelaxed volume of the PMSP membrane was relaxed, and the molecular motion of carbons dropped, suggesting that the decrease in the microvoids caused a tighter chain packing. The copolymer and blend membrane had stable permeability compared to the PMSP. In particular, the addition of a small amount of the PP structure provided excellent stability with high gas permeability. A decrease in the unrelaxed volume of modified membranes was hardly observed with age; however, the molecular motion of some carbons slightly changed. This change did not affect the gas permeability. In this case, a larger unrelaxed volume was probably a dominant factor in the gas permeation of the PMSP rich membranes relative to the molecular motion in the T₁ measurement. © 1997 John Wiley & Sons, Inc.     

“Self‐Lockable” Liquid Crystalline Diels–Alder Dynamic Network Actuators with Room Temperature Programmability and Solution Reprocessability

Novel main‐chain liquid crystalline Diels—Alder dynamic networks (LCDANs) were prepared that exhibit unprecedented ease for actuator programming and reprocessing compared to existing liquid crystalline network (LCN) systems. Following cooling from 125 °C, LCDANs are deformed with aligned mesogens self‐locked at room temperature by slowly formed Diels–Alder (DA) bonds, which allows for the formation of solid 3D actuators capable of reversible shape change, and strip walker and wheel‐capable light‐driven locomotion upon either thermally or optically induced order–disorder phase transition. Any actuator can readily be erased at 125 °C and reprogrammed into a new one under ambient conditions. Moreover, LCDANs can be processed directly from melt (for example, fiber drawing) and from solution (for example, casting tubular actuators), which cannot be achieved with LCNs using exchangeable covalent bonds. The combined attributes of LCDANs offer significant progress toward developing easily programmable/processable LCN actuators.     

Ordered nanostructures at two different length scales mediated by temperature: A triphenylene‐containing mesogen‐jacketed liquid crystalline polymer with a long spacer

A mesogen‐jacketed liquid crystalline polymer (MJLCP) containing triphenylene (Tp) moieties in the side chains with 12 methylene units as spacers (denoted as PP12V) was synthesized. Its liquid crystalline (LC) phase behavior was studied with a combination of solution ¹H NMR, solid‐state NMR, gel permeation chromatography, thermogravimetric analysis, polarized light microscopy, differential scanning calorimetry, and one‐ and two‐dimensional wide‐angle X‐ray diffraction. By simply varying the temperature, two ordered nanostructures at sub‐10‐nm length scales originating from two LC building blocks were obtained in one polymer. The low‐temperature phase of the polymer is a hexagonal columnar phase (Φ_H, a = 2.06 nm) self‐organized by Tp discotic mesogens. The high‐temperature phase is a nematic columnar phase with a larger dimension (a′ = 4.07 nm) developed by the rod‐like supramolecular mesogen—the MJLCP chain as a whole. A re‐entrant isotropic phase is found in the medium temperature range. Partially homeotropic alignment of the polymer can be achieved when treated with an electric field, with the polymer in the Φ_H phase developed by the Tp moieties. The incorporation of Tp moieties through relatively long spacers (12 methylene units) disrupts the ordered packing of the MJLCP at low temperatures, which is the first case for main‐chain/side‐chain combined LC polymers with MJLCPs as the main‐chain LC building block to the best of our knowledge. The relationship of the molecular structure and the novel phase behavior of PP12V has implications in the design of LC polymers containing nanobuilding blocks toward constructing ordered nanostructures at different length scales. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 295–304     

PVT and oscillatory tests to analyze pressure effects on polypropylene/Rodrun LC3000 blends: Determination of the pressure dependency of the viscosity

A combined analysis of Pressure-Volume-Temperature (PVT), Dynamic Mechanical Thermal Analysis (DMTA) and oscillatory flow measurements for blends of a polypropylene (PP) with a commercial liquid crystalline polymer (Rodrun LC3000) is presented. This analysis allows the determination of the pressure-viscosity coefficient b = ∂lnη₀/∂P. This coefficient depends on the Rodrun LC3000 content, increasing with it and is of the same order of magnitude as values reported for several commercial polymers showing a similar dependence of the viscosity on pressure. The analysis of the pressure dependence of Tg (related to b) leads to the conclusion that the number of segments involved in the glass transition of PP increases with the Rodrun LC3000 content, thus demonstrating that the polymers are not totally immiscible. As far as the authors know, this is the first time that the dependence of the viscosity on the pressure has been reported for thermoplastic/liquid crystalline polymer blends.     

Permeability and morphology of poly(cis‐butadiene)/ester‐ether liquid crystal composite membranes

Various amounts of diethylene glycol bis[4‐(4′‐ethoxybenzoyloxy)benzoate] (DEBEB) were added into a poly(cis‐butadiene) (PB) membrane to improve its gas permeation ability. This type of rubber/liquid crystal (LC) composite membranes showed two obvious characteristics that are different from the gas permeation behavior reported in previous literature: (1) The permeabilities to O₂, N₂, and CO₂ were enhanced at room temperature, for example, the permeabilities for the PB/DEBEB (90/10) membrane were higher above six times than those of PB membrane under the same conditions. It is suggested that the interface microvoids probably existed on pontes between polar crystal domains and nonpolar PB matrix. (2) All relationships between the permeability coefficient (P) and temperature (T) were characterized by N‐shape, that is, there were the peaks and valleys on the P‐T curves. Furthermore, morphology studies demonstrated that when DEBEB content in the membranes was above 10 wt %, it was spherically dispersed and embedded in the PB matrix in a crystal domain state. Gas permeation characteristics of the composite membranes were appropriately interpreted as together influence results of DEBEB phase transition behavior and the membrane morphology. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1833–1840, 2000     

Nano/subnano-tuning of porous ceramic membranes for molecular separation

In sol–gel processing, porous ceramic membranes can be prepared by sol-coating porous substrates and drying for gelling, followed by a firing process. Ceramic membranes prepared by sol–gel processing can be categorized into amorphous materials such as silica, and crystalline materials such as alumina and titania. Amorphous silica networks, which can be prepared by the polymeric sol route, have ultra-microporous pores that allow small molecules such as helium and hydrogen to permeate. On the other hand, crystalline materials, which are mostly prepared by the colloidal sol route, have nano-sized pores in the range of one to several nanometers. In this article, sol–gel derived SiO₂ and TiO₂ membranes with controlled pore sizes in the range of sub-nano to nanometers will be reviewed with respect to membrane preparation and to their application in the separation of the gas and liquid phases. Ceramic membranes with high performance can be obtained by precise control of membrane structures (pore size, pore size distribution, thickness, pore shape, etc.) and membrane materials (SiO₂, TiO₂, composite oxide, hybrid materials, etc.). Nano/subnano-tuning of porous ceramic membranes is quite important for the improvement of membrane permeability and selectivity.     

Thermal and UV shape shifting of surface topography

The confinement of LCE materials into surface monodomains via micropatterning leads to the formation of reversible, shape-shifting surface patterns. The individual features are liquid crystalline monodomains, and by switching to an isotropic state using light or heat, the features switch between imprinted circular features and anisotropic liquid crystalline features.     

Characterization and gas permeation of polycarbonateliquid crystal composite membrane

Polymer/liquid crystal composite membranes were cast from a 1,2-dichloroethane solution of polycarbonate (PC) and N-(4-ethoxybenzylidene-4'-n- butylaniline) (EBBA). The mixing state of the polymer/liquid crystal composite membrane was investigated on the basis of differential scanning calorimetry, x-ray, density, sorption isotherm and sorption—desorption studies and also by electron microscopic observations. EBBA molecules in the composite membrane exist in an almost molecularly dispersed state up to an EBBA fraction of 30 wt%, and in the case of EBBA fractions above 30 wt% form a crystal domain as the mutual continuous phase among the network of polycarbonate fibrils. The composite membrane containing EBBA of 60 wt% can be handled as a homogeneous medium when considering gas permeation.The diffusive permeability coefficient to water reveals a distinct jump in the vicinity of the crystal—liquid crystal phase transition temperature of EBBA. The permeability coefficients, P, to hydrocarbon gases increases 100-200 times over several degrees in the phase transition temperature range. P for hydrocarbon gases decreases with increasing number of carbon atoms below the phase transition temperature, but increases with increasing number of carbon atoms above it. These results suggest that the permeation process is predominantly controlled by diffusion mechanism below the transition temperature of EBBA, while the solubility factor significantly affects gas permeation above it.     

Changes of electrochemical responses of the bulk solution species by thermotropic permeability of liquid crystalline membranes coated on electrodes

Liquid crystalline/polymer composite membrane-coated electrodes were prepared by casting a 1,2-dichloroethane solution of N-(4-ethoxybenzylidene)-4′-n-butylaniline (EBBA) and polycarbonate (PC) on an electrode surface. The temperature-dependence of the permeability of the EBBA/PC composite membrane on electrodes to Fe(CN)^3?₆ ion as a solution-phase redox ion was investigated by means of hydrodynamic voltammetry at a rotating disk electrode. The permeability changed with temperature over the range of the crystalline-nematic-phase transition temperature of EBBA. It is demonstrated that the observed temperature-dependence of the permeability reflects the thermotropic properties of EBBA in the EBBA/PC composite membrane. Furthermore, the dependence of the limiting current of the steady-state current-potential curves for the reduction of Fe(CN)^—₆ at the EBBA/PC composite membrane-coated electrode upon the membrane thickness, the blend ratio of EBBA and PC and the concentration of Fe(CN)^3?₆ in a bulk solution was examined in order to understand the transport process of Fe(CN)^?3₆ through the EBBA/PC composite membrane from the membrane/solution interface to the electrode/membrane interface. The transport process of Fe(CN)^3?₆ within the membrane was found to obey Fick's Law.     

Fluorescence study of a thermotropic liquid crystal: Bis (p-hexyloxyphenyl) terephthalate

The microstructure of the low molecular weight thermotropic liquid crystal, bis(p-hexyloxyphenyl)terephthalate (PP6), was analysed by fluorescence. The material has an emission around 400 nm in its various liquid crystalline phases, but this emission disappears in the isotropic phase. The emission was attributed to fluorescence from an intermolecular ground state complex between two different chromophores of PP6 based on fluorescence experiments of model compounds and dilute PP6 solutions. No peak shifts were observed on changing temperature, while the fluorescence intensity decreased as the temperature was increased. The fluorescence intensity changed dramatically at the phase transitions. An abrupt change in the fluorescence intensity was observed on changing depending on the temperature especially at the smectic-nematic transition temperature. Thus, the intermolecular fluorescence of the liquid crystal is greatly affected by the phase structure and the order of liquid crystalline phase.