Structure formation of liquid-crystalline isotropic AB block copolymers in nematic solvents

AB block copolymers with an isotropic and a nematic block are synthesized by living anionic copolymerization of isotropic and mesogenic methacrylates. The complete phase diagrams of the corresponding homopolymers with the nematic solvent have been established. In dilute solution (0.2 to 5% by weight) in a low-molar-mass nematic solvent, the copolymers exhibit two different types of structure formation. Polymers with high isotropic block fraction form irreversible networks as a results of phase separation followed by vitrification of the polymer-rich phase. Polymers with high nematic block fraction on the other hand form thermoreversible threadlike structures perfectly ordered parallel to the director of the nematic solvent. These structures cannot be explained by a macroscopic phase separation process but more likely by a formation of micellar-like aggregates.     

Preparation of a unique microporous structure via two step phase separation in the course of drying a ternary polymer solution

A unique porous polymeric film was prepared by drying a ternary polymer solution: a polystyrene (PS), polyethylene glycol (PEG), and toluene solution. Highly ordered micropores, ranging from 5 to 12 mum in diameter, were formed on the film surface, and the rim of each micropore was surrounded by a ring of PEG. The effects of the weight ratio of the polymer blend and molecular weight of the polymer (PEG) on the porous structure were investigated. Based on in situ visual observation and light scattering measurements, the formation mechanism of the porous structure was speculated to be a two step phase separation: the phase separation into PEG-rich and PEG-poor (i.e., PS-rich) phases occurred first at the surface area of the ternary solutions, where polymers were condensed due to solvent evaporation. The PEG-rich phase became droplets and had an ordered structure on the surface. The PEG-poor phase became a matrix where PS and solvent coexisted as a single phase solution. Secondary phase separation then followed in the PEG droplets, which was induced by further solvent evaporation, and formed into solvent-rich and PEG-rich domains within the droplets. Solvent evaporation and secondary phase separation created a cavity structure in each PEG droplet structured on the film surface.     

Chain conformations and phase separation in polymer solutions with varying solvent quality

Molecular dynamics simulations are used to investigate the conformations of a single polymer chain, represented by the Kremer-Grest bead-spring model, in a solution with a Lennard-Jones liquid as the solvent when the interaction strength between the polymer and solvent is varied. Results show that when the polymer-solvent interaction is unfavorable, the chain collapses as one would expect in a poor solvent. For more attractive polymer-solvent interactions, the solvent quality improves and the chain is increasingly solvated and exhibits ideal and then swollen conformations. However, as the polymer-solvent interaction strength is increased further to be more than about twice the strength of the polymer-polymer and solvent-solvent interactions, the chain exhibits an unexpected collapsing behavior. Correspondingly, for strong polymer-solvent attractions, phase separation is observed in the solutions of multiple chains. These results indicate that the solvent becomes effectively poor again at very attractive polymer-solvent interactions. Nonetheless, the mechanism of chain collapsing and phase separation in this limit differs from the case with a poor solvent rendered by unfavorable polymer-solvent interactions. In the latter, the solvent is excluded from the domain of the collapsed chains while in the former, the solvent is still present in the pervaded volume of a collapsed chain or in the polymer-rich domain that phase separates from the pure solvent. In the limit of strong polymer-solvent attractions, the solvent behaves as a glue to stick monomers together, causing a single chain to collapse and multiple chains to aggregate and phase separate.     

Semi-interpenetrating polymer networks with controllable morphology - arrest of demixing by thermoreversible gelation

Semi-interpenetrating polymer networks with well defined morphologies were obtained using a three-step process, separating morphology formation and polymerization/crosslinking. Different phase textures were formed when (spinodal) liquid/liquid demixing of a solution of atactic polystyrene in methacrylate monomers was arrested by thermoreversible gelation (vitrification) of the polymer-rich phase at a desired stage. Subsequent UV-polymerization of the methacrylate allowed to study the morphology by transmission electron microscopy. Phase diagrams of polymer solutions with low and high viscosities are reported. Depending on the initial solution viscosities and the applied cooling conditions, morphologies both with a dispersed as well with a continuous polystyrene phase could be obtained at PS concentrations already below 10 %. Mechanical measurements indicated only partial demixing in the semi-IPN's.     

A qualitative skin layer formation mechanism for membranes made by dry/wet phase inversion

Optimized membranes made by a dry/wet phase inversion process using forced-convective evaporation consist of an ultrathin and pore-free skin layer supported by a nodular transition layer underlying open-cell, sponge-like substructure. It is suggested that the out-ermost region of such case membranes undergo phase separation by spinodal decomposition in the initial stages of the evaporation process. As a result of the small scale of phase separation present in polymer?solvent systems, an appreciable capillary pressure occurs in the interstitial space filled with the polymer-poor phase in contact with air. The resulting force acts normal to the membrane–air interface, which tends to consolidate the polymer-rich phase to form a nonporous surface layer. © 1993 John Wiley & Sons, Inc.     

Dynamics of liquid–liquid demixing: mesoscopic simulations of polymer solutions

In this article, the mesoscopic simulation method dissipative particle dynamics (DPD) is applied to study the dynamics of polymer–solvent liquid–liquid phase separation. It will be shown that the degree of branching has a pronounced effect on the radius of gyration and the centre of mass diffusion of the polymer. Based on the simulation results it can be concluded that the difference in chemical potential between the mixed and the demixed state is the main driving force behind the centre of mass diffusion (and thus phase separation), rather than the reduced radius of gyration due to to polymer chain collapse.     

Microscale fish bowls: a new class of latex particles with hollow interiors and engineered porous structures in their surfaces

Microscale fish bowls, hollow particles with engineered holes in their surfaces, were prepared using two different methods. In the first method, commercial latex beads suspended in water were swollen with a good solvent of the polymer, followed by freezing with liquid nitrogen and evaporation of the solvent below 0 degrees C. While one big hole was generated when the amount of solvent used for the swelling was relatively low, small holes could be produced in the outer surface of each bowl by increasing the degree of swelling. The porosity and pore structure show a similar dependence on the degree of swelling for both amorphous and semicrystalline polymers even though they are supposed to exhibit different phase behaviors during the freezing and solvent evaporation processes. In the second method, a polymer emulsion in water was prepared and then frozen with liquid nitrogen, followed by solvent evaporation below 0 degrees C. The porosity and pore structure could be controlled by adjusting the concentration of the polymer solution used to prepare the emulsion. As for encapsulation, the bowl-shaped particles could be transformed back into solid beads via thermal annealing at a temperature near the glass transition temperature of the polymer or by adding a good solvent of the polymer to the colloidal suspension. In a proof-of-concept experiment, microscale fish bowls were fabricated from poly(caprolactone), quickly loaded with a fluorescent dye, and sealed through thermal annealing. The encapsulated dye could then be slowly released in a phosphate buffered saline, suggesting their potential use as a new class of microscale capsules for drug delivery.     

Phase separation and gelation of polymer-dispersed liquid crystals

Polymerization-induced phase separation in polymer-dispersed liquid crystal is studied by computer simulations in two dimensions. The domain morphology resulting from phase separation is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter, taking into account the viscoelastic effects and gelation due to polymerization. Comparing the morphology of phase separation by temperature quench, it is shown that the viscoelastic effects and gelation enable the polymer-rich phase to form a stable interconnected domain even when the polymer component is minority. The experimental evidence consistent with this characteristic feature is also given.     

Liquid-liquid equilibria of polyrotaxane and poly(vinyl alcohol)

Liquid–liquid equillibria (LLE) of the tertiary system of hydroxypropylated polyrotaxane (HPPR)–poly(vinyl alcohol) (PVA)–solvent have been investigated by focusing on the internal structures of HPPR–PVA blend gels. The phase diagrams of the HPPR–PVA aqueous systems displayed two liquid phases at a high concentration and molecular weight of PVA. This result was consistent with the prediction of the Flory–Huggins lattice model. On the contrary, the HPPR–PVA–DMSO system exhibited only a single phase. The HPPR–PVA blend gels crosslinked in dimethylsulfoxide (DMSO) were highly transparent over a wide concentration range, while the gels prepared in water were opaque at high polymer concentrations. Spherical domains were observed in the opaque gels by laser scanning confocal microscopy, and the sizes of the domains were significantly dependent on the amount of cross-linking reagent utilized. These results indicated that the transparency of the HPPR–PVA blend gels was strongly affected by the competition between the liquid–liquid two-phase separation and the crosslinking HPPR and PVA polymers during the preparation of the blend gels.     

Radiolytic synthesis and characterization of Ag-PVA nanocomposites

The Ag-PVA nanocomposites with different contents of inorganic phase were prepared by reduction of Ag⁺ ions in aqueous PVA solution by gamma irradiation followed by solvent evaporation. Optical properties of the colloidal solutions and the nanocomposite films were investigated using UV-vis spectroscopy. Structural characterization of the Ag nanoparticles was performed by TEM and XRD. Interaction of the Ag nanoparticles with polymer matrix and the heat resistance of the nanocomposites were followed by IR spectroscopy and DSC analysis. IR spectra indicated that Ag nanofiller interact with PVA chain over OH groups. The changes of heat resistance upon the increase of the content of inorganic phase are correlated to the adsorption of polymer chains on the surface of Ag nanoparticles.     

Controlled assembly of silica microspheres in spherically confined polymer particles by using self-organized precipitation (SORP) method

Assembly of submicron-sized microspheres has received much attention due to its high potential for wide variety of applications. We have developed a preparation method of polymer particles by simple mixing of a poor solvent into the polymer solution followed by evaporation of a good solvent. By using this technique, silica nanoparticles and polymer composite particles were prepared. Preparation of three-dimensional assemblies of silica particles in polymer particles and composite Janus particles are shown.     

Thermoplastic polymer‐dispersed liquid crystals prepared from solvent‐induced phase separation with predictions using solubility parameters

The optical effects of liquid crystals can be realized when the mesogens are dispersed in a supporting and stabilizing polymer phase. Thermoplastics were chosen for their structural reversibility and ease of fabrication of polymer‐dispersed liquid crystals (PDLCs) from solution via solvent‐induced phase separation (SIPS). The component match and tuning in PDLCs was achieved in a common solvent through predictions of solubility parameters. The PDLCs were first prepared using SIPS and were then exposed to thermal treatments on a hot stage polarizing microscope or in a differential scanning calorimeter. At elevated temperatures the polymer and mesogen may become miscible, while upon cooling thermally induced phase separation (TIPS) should occur, preferably above the isotropic–nematic transition temperature. The nematic phase existed within disperse phase droplets that were stabilized and supported by the matrix polymer. The temperature range of the nematic phase was extended in the PDLC configuration. The droplet size was important for liquid crystalline optical behaviour. Polymer–mesogen interactions, identified through solubility parameters, were important in ensuring sufficient but not coarse phase separation.     

Prediction of vapor–liquid and liquid–liquid equilibria for polymer systems: Comparison of activity coefficient models

A large number of equations of state and activity coefficient models capable of describing phase equilibria in polymer solutions are available today, but only a few of these models have been applied to different systems. It is therefore useful to investigate the performance of existing thermodynamic models for complex polymer solutions which have not yet been widely studied. The present work studies the application of several activity coefficient models [P.J. Flory, Principles of Polymer Chemistry, Cornell University Press, New York, NY, 1953; T. Oishi, J.M. Prausnitz, Estimation of solvent activities in polymer solutions using a group-contribution method, Ind. Eng. Chem. Process Design Dev. 17 (1978) 333; H.S. Elbro, A. Fredenslund, P. Rasmussen, A new simple equation for the prediction of solvent activities in polymer solutions, Macromolecules 23 (1990) 4707; G.M. Kontogeorgis, A. Fredenslund, D. Tassios, Simple activity coefficient model for the prediction of solvent activities in polymer solutions, Ind. Eng. Chem. Res. 32 (1993) 362; C. Chen, A segment-based local composition model for the Gibbs energy of polymer solutions, Fluid Phase Equilib. 83 (1993) 301; A. Vetere, Rules for predicting vapor–liquid equilibria of amorphous polymer solutions using a modified Flory–Huggins equation, Fluid Phase Equilib. 97 (1994) 43; C. Qian, S.J. Mumby, B.E. Eichinger, Phase diagrams of binary polymer solutions and blends, Macromolecules 24 (1991) 1655; Y.C. Bae, J.J. Shim, D.S. Soane, J.M. Prausnitz, Representation of vapor–liquid and liquid–liquid equilibria for binary systems containing polymers: applicability of an extended Flory–Huggins equation, J. Appl. Polym. Sci. 47 (1993) 1193; G. Bogdanic, J. Vidal, A segmental interaction model for liquid–liquid equilibrium calculations for polymer solutions, Fluid Phase Equilibria 173 (2000) 241] and activity coefficient from equations of state [F. Chen, A. Fredenslund, P. Rasmussen, Group-contribution Flory equation of state for vapor–liquid equilibria en mixtures with polymers, Ind. Eng. Chem. Res. 29 (1990) 875; M.S. High, R.P. Danner, Application of the group contribution lattice—fluids EOS to polymer solutions, AIChE J. 36 (1990) 1625]. The evaluation of these models was carried out both at infinite dilution and at finite concentrations and the results compared to experimental data. Furthermore, liquid–liquid equilibrium predictions for binary polymer solutions using six activity coefficient models are compared in this work. The parameters were estimated for all the models to achieve the best possible representation of the reported experimental equilibrium behavior.     

Determination of anthocyanins in wine based on flow-injection, liquid--solid extraction, continuous evaporation and high-performance liquid chromatography--photometric detection

A continuous method, easy to automate, for the determination of anthocyanins in wine based on the coupling of continuous liquid–solid extraction, evaporation, HPLC individual separation and photometric detection is proposed. The target analytes are removed from the wine in a continuous fashion using a C₁₈ minicolumn and eluted with an aqueous solution (pH 2) with 16% acetonitrile. The eluted fraction is concentrated by solvent evaporation assisted by heat and dragging off the vapour using a flow of N₂. For in-line preconcentration, a continuous evaporation module was designed and located in the manifold between the solid-phase minicolumn and the injection valve of the chromatograph. In this way, injection of the sample into the dynamic system leads the plug through it for liquid–solid extraction of the anthocyanins, partial evaporation of the eluent (with a preconcentration factor as required) and transport to the high-pressure injection valve of the chromatograph, where individual separation and subsequent photometric detection take place. The method thus developed for the determination of malvidin-3-glucoside, cyanidin-3-glucoside and peonidin-3-glucoside anthocyanins in Spanish red wines is more sensitive than the batch manual method based on the same steps, has better linearity of the calibrations curves with lower detection limits and much wider determination range for the most abundant anthocyanins in wine. In addition, the method can be fully automated with low acquisition and maintenance costs.     

Tailoring poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) microstructure and physicochemical properties by exploring its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (PVDF‐CTFE) membranes were prepared by solvent casting from dimethylformamide (DMF). The preparation conditions involved a systematic variation of polymer/solvent ratio and solvent evaporation temperature. The microstructural variations of the PVDF‐CTFE membranes depend on the different regions of the PVDF‐CTFE/DMF phase diagram, explained by the Flory‐Huggins theory. The effect of the polymer/solvent ratio and solvent evaporation temperature on the morphology, degree of porosity, β phase content, degree of crystallinity, mechanical, dielectric, and piezoelectric properties of the PVDF‐CTFE polymer were evaluated. In this binary system, the porous microstructure is attributed to a spinodal decomposition of the liquid‐liquid phase separation. For a given polymer/solvent ratio, 20 wt % , and higher evaporation solvent temperature, the β phase content is around 82% and the piezoelectric coefficient, d₃₃, is ? 4 pC/N © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 761–773     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Morphology development of main‐chain liquid crystalline polymer fibers during solvent evaporation

A nonequilibrium thermodynamic approach has been developed for describing the emergence of fiber morphologies from a liquid crystalline polymer solution undergoing solvent evaporation, including fibrillar structures, concentric rings, and spiral structures. We utilized Matsuyama–Kato free energy for main‐chain liquid crystalline polymer (MCLCP) solutions, which is an extension of Maier–Saupe theory for nematic ordering and incorporates a chain‐stiffening, combined with Flory‐Huggins free energy of mixing. Temporal evolution of the concentration and nematic order parameters pertaining to the above free energy density of liquid crystalline polymer solution was simulated in the context of time‐dependent Ginzburg–Landau theory coupled with the solvent evaporation rate equation under the quasi‐steady state assumption. The emerged morphological patterns are discussed in relation to the phase diagram of the MCLCP solution and the rate of solvent evaporation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 429–435, 2007     

Application of in-situ formed polymer-based dispersive solid phase extraction in combination with solidification of floating organic droplet-based dispersive liquid–liquid microextraction for the extraction of neonicotinoid pesticides from milk samples

An in-situ formed polymer–based dispersive solid phase extraction in combination with solidification of floating organic droplet-based dispersive liquid–liquid microextraction was developed for the extraction of neonicotinoid pesticides from milk samples. The extracted analytes were determined using high-performance liquid chromatography–diode array detector. In this approach, after precipitating the proteins of milk using a zinc sulfate solution, the supernatant phase (containing sodium chloride) was transferred into another glass test tube, and a homogenous solution of polyvinylpyrrolidone and a suitable water-miscible organic solvent was rapidly injected into it. By this step, the polymer particles were re-produced and the analytes were extracted onto the sorbent surface. In the following step, the analytes were eluted with an appropriate organic solvent to use in the following solidification of floating organic droplet-based dispersive liquid–liquid microextraction step that was done to acquire the low limits of detection. Under the optimized conditions, satisfactory results consisting of low limits of detection (0.13–0.21 ng/ml) and quantification (0.43–0.70 ng/ml), high extraction recoveries (73%–85%), and enrichment factors (365–425), and good repeatability (relative standard deviations equal or less than 5.1% and 5.9% for intra- and inter-day precisions, respectively) were obtained.     

Thermoplastic polymer-dispersed liquid crystals prepared from solvent-induced phase separation with predictions using solubility parameters

The optical effects of liquid crystals can be realized when the mesogens are dispersed in a supporting and stabilizing polymer phase. Thermoplastics were chosen for their structural reversibility and ease of fabrication of polymer-dispersed liquid crystals (PDLCs) from solution via solvent-induced phase separation (SIPS). The component match and tuning in PDLCs was achieved in a common solvent through predictions of solubility parameters. The PDLCs were first prepared using SIPS and were then exposed to thermal treatments on a hot stage polarizing microscope or in a differential scanning calorimeter. At elevated temperatures the polymer and mesogen may become miscible, while upon cooling thermally induced phase separation (TIPS) should occur, preferably above the isotropic-nematic transition temperature. The nematic phase existed within disperse phase droplets that were stabilized and supported by the matrix polymer. The temperature range of the nematic phase was extended in the PDLC configuration. The droplet size was important for liquid crystalline optical behaviour. Polymer-mesogen interactions, identified through solubility parameters, were important in ensuring sufficient but not coarse phase separation.     

Characterisation of polymerisation-induced phase separation process in polymer-dispersed liquid crystals based on hydroxyalkyl-methacrylate matrices

Hydroxyalkyl-methacrylates are very well-known hydrogel-forming biocompatible polymers. In this work, polymer-dispersed liquid crystals (LCs) based on hydroxyethyl- and hydroxypropyl-methacrylate (HEMA and HPMA) matrices are synthesised and characterised. Two different LCs from the cyano-biphenyl family (4?-pentyl-4-cyanobiphenyl [5CB] and 4?-octyl-4-cyanobiphenyl [8CB]) are used. Polymerisation kinetics, phase transitions, and morphologies generated during the polymerisation-induced phase separation process are analysed. Phase separation is observed at very low conversions, where a polymer-rich phase is initially segregated and this produces an increase in the low-conversion polymerisation rate (ascribed to the auto-acceleration effect of free-radical polymerisations in the polymer-rich phase). The liquid crystalline transition temperature decreases as the concentration of LC decreases, indicating that this phase is impurified. The liquid crystal 8CB is found to be less miscible than 5CB with the polymer matrices, so the LC-rich phase for 5CB is more impurified and its total volume in the material is smaller.