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.     

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.     

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). I. Miscibility and thermal properties

The miscibility and thermal properties of polyethylene oxide(PEO)/oligoester resin (OER) blends and PEO/crosslinked polyester (PER) blends were studied by differential scanning calorimetry (DSC). The effect of quenching process on the crystallization behavior of PEO for these two systems were investigated and discussed in details. It has been found that a single, composition dependent glass transition temperature (T_g) was observed for all the blends, indicating that the two systems are miscible in the amorphous state at overall compositions. From the melting point depression of PEO, the interaction parameter χ₁₂ for PEO/OER blends and that for PEO/PER blends were found to be −1.29 and −2.01, respectively. The negative values of χ₁₂ confirmed that both PEO/OER blends and PEO/PER blends are miscible in the molten state. Quenching process has a greater hindrance on the crystallization of PEO/OER blends than on that of PEO/PER blends. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3161–3168, 1997     

Diphenol miscibility effect on the immiscible polyester/polyether binary blends through intermolecular hydrogen‐bonding interaction

Miscibility and hydrogen bonding interaction have been investigated for the binary blends of poly(butylene adipate‐co‐44 mol % butylene terephthalate)[P(BA‐co‐BT)] with 4,4'‐thiodiphenol (TDP) and poly(ethylene‐ oxide)(PEO) with TDP; and the ternary blends of P(BA‐co‐BT)/PEO/TDP by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The DSC results indicated that the binary blends of P(BA‐co‐BT)/TDP and PEO/TDP were miscible because each blend showed only one composition‐dependent glass‐transition over the entire range of the blend composition. The formation of intermolecular hydrogen bonds between the hydroxyl groups of TDP and the carbonyl groups of P(BA‐co‐BT), and between the hydroxyl groups of TDP and the ether groups of PEO was confirmed by the FTIR spectra. According to the glass‐transition temperature measured by DSC, P(BA‐co‐BT) and PEO, their binary blends were immiscible over the entire range of blend composition, however, the miscibility between P(BA‐co‐BT) and PEO was enhanced through the TDP‐mediated intermolecular hydrogen bonding interaction. It was concluded that TDP content of about 5–10% may possibily enhance miscibility between P(BA‐co‐BT) and PEO via a hydrogen bonding interaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2971–2982, 2004     

不同醇对聚合物分散液晶光聚合动力学及其电光特性的影响

以丙烯酸-2-乙基己酯(EHA)、二甲基丙烯酸乙二酯(EDMA)/季戊四醇四丙烯酸酯(PETTA)为混合单体、液晶P0616A为液晶相、Irgacure 184为光引发剂,通过UV光引发制备了聚合物分散液晶(PDLCs),研究了不同烷基链长醇,即乙醇(EtOH)、正丁醇(nBA)、正己醇(nHA)、正辛醇(nOA)和正十四醇(nTA)对体系光聚合动力学及其PDLCs液晶相变温度及电光特性的影响.结果表明引入醇分子显著加快了丙烯酸酯/液晶复合体系的光聚合反应速率,提高了单体的最终转化率,其中以正丁醇体系最为明显.随着醇分子烷基链的增长,体系的转化率趋于降低,但依然明显高于不含醇的体系.醇分子的加入降低了PDLCs中液晶相的TNI,且随着醇分子烷基链长的增长,PDLCs液晶相的TNI总体上呈降低的趋势.醇分子的加入增加了PDLCs液晶微区中向列相液晶的含量,而含正丁醇和正十四醇的体系液晶微区中向列相液晶低于其它3个含醇体系.醇分子的加入明显降低了PDLCs的阈值电压和饱和电压以及对比度.结合体系的光聚合速率和单体转化率,正丁醇是改善PDLCs性能的最佳选择.     

Modification of the lyotropic liquid crystalline microstructure of amphiphilic block copolymers in the presence of cosolvents

This article reviews the results of recent investigations on the macroscopic (phase behavior) and microscopic (microstructure) aspects of the role of cosolvents on the self-assembly of amphiphilic copolymers. A comprehensive account of the systematic studies performed in ternary isothermal systems consisting of a representative poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer (Pluronic P105, EO₃₇PO₅₈EO₃₇), water and a polar cosolvent (such as glycerol, propylene glycol or ethanol) is presented. The effect of cosolvents on the copolymer phase behavior is quantified in terms of the highest cosolvent/water ratio able to maintain the liquid crystalline structures. The effect of cosolvents on the microstructure of the lyotropic liquid crystals is quantified in terms of the degree of relative swelling per cosolvent content per copolymer content, a parameter that characterizes the given cosolvent and copolymer. The set of correlations on the cosolvent effects on the phase behavior or microstructure to the cosolvent physicochemical characteristics (such as octanol/water partition coefficient or solubility parameter) have led to the development of a hypothesis that accounts for the cosolvent effects on the self-assembly of PEO–PPO–PEO block copolymers and can be used to predict them. The rich structural diversity and the potential for a precise and convenient modification of the lyotropic liquid crystalline microstructure of the PEO–PPO–PEO block copolymers is discussed in comparison to the phase behavior of the low-molecular nonionic surfactants.     

Unusual phase behavior in mixtures of poly(ethylene oxide) and ethyl alcohol

Poly(ethylene oxide) (PEO), soluble in both aqueous and organic solvents, is one of the most intriguing polymers. PEO solution properties have been extensively studied for decades; however, many of the studies have focused on specific properties, such as clustering, of PEO in aqueous solutions, and the behavior of PEO in organic solvents has not been adequately explored. The results presented here demonstrate that PEO crystallizes into a lamellar structure in ethyl alcohol after the mixture is quenched to room temperature from a temperature above the crystal melting point. Above the melting temperature, PEO completely dissolves in ethyl alcohol, and the mixture exhibits regular polymer solution thermodynamic behavior with an upper critical solution temperature (UCST) phase diagram. Remarkably, the UCST phase boundary is significantly below the melting temperature, and this indicates that the system undergoes a crystallization process before the phase separation can occur upon cooling and, therefore, possesses an unusual phase transition. The phase transition from the crystalline state to the miscible solution state is reversible upon heating or cooling and can be induced by the addition of a small amount of water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 557–564, 2006     

SEC with UV and ELSD detection for analysis of gamma-irradiated PS-radiation-grafted P(VDF/HFP) films

Summary Thin poly(vinylidene fluoride/hexafluoropropylene) (P(VDF/HFP)) films ahve been irradiated with gammarays to induce the initiation of styrene grafting by the indirect method. To obtain a better understanding of the radiation-grafting process we have used size exclusion chromatography (SEC) to study the effect of irradiation of this polymer and the evolution of the molecular weights of the polystyrene (PS) grafted chains as a function of the grafting time. Pristine, irradiated and PS radiation-grafted samples have been compared. We present evidence that the gamma irradiation induces both scission and crosslinking of the P(VDF/HFP) chains. We show that the average molecular weights of the PS grafted chains increase with grafting time and that the asymmetry of the chromatographic peak increases also. These grafted chains have molecular weights much higher than those of pristine P(VDF/HFP) and they cannot be confused with PS homopolymer chains, which have higher molecular weights as both, pristine and radiation-grafted P (VDF/HFP). Reversed-phase high-performance liquid chromatography (RPHPLC) has shown the absence of additives in pristine P(VDF/HFP) and has provided evidence of the presence of oligomers.     

Polymer battery R&D in the U.S.

Polymer electrolytes that have been developed for battery applications fall into two general classes, neat or “pure” polymer and plasticized or gel in which the polymer is combined with a conducting organic electrolyte. The polyethylene oxide (PEO) and its modifications are typical of the “pure” polymer electrolytes. They have poor conductivity at room temperatures, but at elevated temperatures, their conductivity is of the order of 10⁻³ to 10⁻⁴ S/cm. The PEO electrolytes have found application in the high temperature (>60°C) lithium metal anode battery systems. The high temperature necessary for good operation makes them unsuitable for use in small consumer appliances. The polymer electrolyte battery development activities have resulted in several high performance battery systems now just entering the market. Not all of the developments have resulted in commercial cell production. The commercialization activities of high performance lithium‐ion (Li‐Ion) batteries have been based on two general plastic polymer systems: poly‐vinylidene difluoride‐hexafluoropropylene copolymer (PVdF‐HFP) and polyacrylates. The polymer cells are expected to have advantages in manufacturing, flexibility, thin cell formats and lightweight packaging. Important parameters in PVdF gel electrolyte performance include the electrolyte type (combination of organic carbonates), temperature, and HFP copolymer content. Li‐Ion coin cells fabricated with a polyolefin separator with either liquid electrolyte or with the PVdF gel polymer electrolyte have equivalent performance.     

Simultaneous prediction of interfacial tension and phase equilibria in binary mixtures: An approach based on cubic equations of state with improved mixing rules

Vapor–liquid interfacial tensions of miscible mixtures have been predicted by applying the gradient theory to an improved Peng–Robinson equation of state. The modified Huron–Vidal mixing rule model has been considered for fitting vapor–liquid equilibrium data of miscible polar and non-polar mixtures and, then, for predicting the interfacial tension of these mixtures. According to results, an accurate and globally stable fitting of the vapor–liquid equilibrium data results on a physically coherent prediction of interfacial tensions in the full concentration range. In addition, we present a criteria based on the geometry of the grand potential function along the interface for assessing the predictive value of the GT. Calculations for subcritical binary mixtures are presented and compared to experimental data and the Parachor method for demonstrating the potential of the unified approach suggested in this work.     

Interphase/interface modification on the dielectric properties of polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) multilayer films for high‐energy density capacitors

Unique three‐component multilayer films with ATBTATBTA configuration were fabricated using forced assembly multilayer coextrusion for novel dielectric systems. The dielectric breakdown strength, displacement–electric field hysteresis, and dielectric spectroscopy of 65‐layer polycarbonate (PC)/tie/poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐HFP)) were investigated with various tie materials. Three different tie materials, poly(methyl methacrylate) (PMMA), styrene‐co‐acrylonitrile copolymer with 30% acrylonitrile content (SAN30), and poly(ethylene terephthalate‐co‐1,4‐cycohexanedimethylene terephthalate) (PETG) were chosen owing to their various degrees of interaction with either P(VDF‐HFP) or PC. The 65‐layer PC/PMMA/P(VDF‐HFP) films exhibited a 25% enhancement in breakdown properties, 50% higher energy density, 40% smaller hysteresis loop areas, and orders of magnitude slower ion migration relative to the 33‐layer PC/P(VDF‐HFP) control. These property improvements are mainly attributed to the localized interactions at PMMA/P(VDF‐HFP) and PMMA/PC interfaces, forming interphase regions. The modified PMMA/P(VDF‐HFP) interphase region can effectively hinder the migration of impurity ions in P(VDF‐HFP), reducing their mobility within the layer. Additionally, a small fraction of PMMA can lead to slightly increased dielectric constant of the composite films owing to strong interaction between PMMA and P(VDF‐HFP). The other two systems with PETG and SAN30 as tie layers exhibited marginal improvements in dielectric properties owing to their weaker interactions with the P(VDF‐HFP) layers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 978–991     

Melting point depression and phase behavior of poly(ether-sulfone) and poly(ethylene oxide) blends: Equation-of-state theory approach

Melting-point depression in miscible polymer blends is interpreted with Flory-Prigogine's equation-of-state theory (FP theory) and Sanchez-Lacombe's lattice fluid theory (LF theory). The equations for equilibrium melting point depression in polymer mixtures are proposed from both the FP and LF theories. For miscible poly(ether-sulfone) (PES)/poly(ethylene oxide) (PEO) blends, the proposed equations are tested. The interaction parameters, X₁₂ in FP theory and ζ₁₂ in LF theory, can be determined with these equations. The theoretically predicted equilibrium melting-point depression is subdivided into three terms, namely, the equation-of-state, the entropy and the contact interaction terms. When the estimated interaction parameters are converted to the heat of mixing by use of both theories, the composition dependence of the heat of mixing can be properly predicted. Using the interaction parameters obtained from the melting-point depression in PES/PEO blends, the spinodal curves are simulated from both the FP and LF theories.     

Elaboration and electro-optic study of a new type of open porosity PDLC

A new polymer dispersed liquid crystal (PDLC) system characterized by easy processing and an open porosity has been elaborated. This PDLC is based on a pre-formed, porous, thin polymer film of a commercially available PVDF-HFP copolymer wetted by the eutectic mixture of cyano bi- and ter-phenyls known as E7 (Merck Ltd, UK). This new process is of interest because of its simplicity, and the fact that there is no risk of intermixing between the liquid crystal and the polymer matrix as occurs in a conventional PDLC. An electric field applied across the thin film results in a change in its transmission, due to the reorientation of the liquid crystal director, as already known for closed porosity PDLCs. The electro-optic properties of this PDLC have been studied and semi-quantitatively interpreted on the basis of the response theory of conventional closed porosity PDLCs.     

Two calorimetric glass transitions do not necessarily indicate immiscibility: The case of PEO/PMMA

Differential scanning calorimetry has been used to examine blends of a poly(ethylene oxide) (PEO), M_n = 300 g/mol, and a poly(methylmethacrylate) (PMMA), M_n = 10,000 g/mol, across the complete composition range. The relatively low molar mass of the PEO minimizes interference from crystallization. In the midrange of composition, ～25–70% PEO, two broad, but distinct, glass transitions are resolved. These are interpreted as distinct glass transitions of the two components, as anticipated by the self‐concentration model of Lodge and McLeish. The composition dependence of the observed transitions is well described by the self‐concentration approach, using lengthscales of approximately two‐thirds of the Kuhn length. The results are compared with previous measurements on PEO/PMMA blends and other miscible systems. The principal, general conclusion is that one should actually expect two glass transitions in a miscible polymer blend or polymer solution; the rule of thumb that two transitions indicate immiscibility is incorrect. Furthermore, attempts to rationalize two transitions on the basis of incomplete segmental mixing, or other unspecified “nanoheterogeneity,” may not be justified in many cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 756–763, 2006     

Solution processing of polymer semiconductor: Insulator blends—Tailored optical properties through liquid–liquid phase separation control

It has been demonstrated that the 0‐0 absorption transition of poly(3‐hexylthiophene) (P3HT) in blends with poly(ethylene oxide) (PEO) could be rationally tuned through the control of the liquid–liquid phase separation process during solution deposition. Pronounced J‐like aggregation behavior, characteristic for systems of a low exciton band width, was found for blends where the most pronounced liquid–liquid phase separation occurred in solution, leading to domains of P3HT and PEO of high phase purity. Since liquid–liquid phase separation could be readily manipulated either by the solution temperature, solute concentration, or deposition temperature, to name a few parameters, our findings promise the design from the out‐set of semiconductor:insulator architectures of pre‐defined properties by manipulation of the interaction parameter between the solutes as well as the respective solute:solvent system using classical polymer science principles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 304–310     

Synthesis and characterization of a vinyl‐terminated benzoxazine monomer and its blends with poly(ethylene oxide)

A vinyl‐terminated benzoxazine (VB‐a), which could be polymerized through ring‐opening polymerization, was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine. This VB‐a monomer was then subjected to blending with poly(ethylene oxide) (PEO), followed by thermal curing, to form poly(VB‐a)/PEO blends. The specific interactions, miscibility, morphology, and thermal properties of these blends were investigated with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Before curing, we found that PEO was miscible with VB‐a, as evidenced by the existence of a single composition‐dependent glass transition temperature (T_g) for each composition. The FTIR spectra revealed the presence of hydrogen‐bonding interactions between the hydroxyl groups of poly(VB‐a) and the ether groups of PEO. Indeed, the ring‐opening reaction and subsequent polymerization of the benzoxazine were facilitated significantly by the presence of PEO. After curing, DMA results indicated that the 50/50 poly(VB‐a)/PEO blend exhibited two values of T_g: one broad peak appeared in the lower temperature region, whereas the other (at ca. 327 °C, in the higher temperature region) was higher than that of pristine poly(VB‐a) (301 °C). The presence of two glass transitions in the blend suggested that this blend system was only partially miscible. Moreover, SEM micrographs indicated that the poly(VB‐a)/PEO blends were heterogeneous. The volume fraction of PEO in the blends had a strong effect on the morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 644–653, 2007     

Reduced OFF-axis haze in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystals (PDLCs) are composite materials formed by micron-sized droplets of liquid crystals (LCs) dispersed in a polymer matrix, which can be turned from an opaque state to a transparent one by application of a suitable electric field. PDLCs have been proposed in applications related to the control of light transmittance on large surfaces (light shutters, displays, rear mirrors). Despite several advantages, PDLCs’ main drawback is haze, i.e. the fast decay of transmission at large viewing angles. In this paper, a method for achieving highly transparent PDLC devices over a wide range of viewing angles is proposed. The method is based on the use of PDLCs with tilted elongated LC droplets and driven by opportune electric fields, which are experimentally calculated and able to ensure an almost constant value for OFF-axis transmittance.     

Biodegradable PEO/cellulose‐based solid–solid phase change materials

A series of poly(ethylene oxide) (PEO) blends with cellulose (CEL) or cellulose derivatives—carboxymethyl cellulose (CMC), cellulose acetate (CAC), and cellulose ether (CET)—has been investigated as phase change materials for thermal energy storage. For PEO/CEL blends solid–solid phase transition has been observed in the whole concentration's range; for PEO/CMC and PEO/CET blends solid–solid phase transition has been found for PEO content 25 or 50 and 25 wt%, respectively. Otherwise, solid–liquid phase transition takes place. MTDSC investigations revealed that for PEO/CEL and PEO/CMC blends transition the strongest recrystallization effect (as evidenced by exothermic effect in reversing heat flow) as melting process occurred. FTIR analysis shows a shift of the stretching vibration bands of both the proton‐donor O? H groups from CEL and PEO due to intermolecular hydrogen interactions between the blends' components. Copyright © 2010 John Wiley & Sons, Ltd.     

Miscible blends of poly(ethylene oxide) with brush copolymers of poly(vinyl alcohol)‐graft‐poly(l‐lactide)

Even though poly(ethylene oxide) (PEO) is immiscible with both poly(l ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA), this article shows a working route to obtain miscible blends based on these polymers. The miscibility of these polymers has been analyzed using the solubility parameter approach to choose the proper ratios of the constituents of the blend. Then, PVA has been grafted with l ‐lactide (LLA) through ring‐opening polymerization to obtain a poly(vinyl alcohol)‐graft‐poly(l ‐lactide) (PVA‐g‐PLLA) brush copolymer with 82 mol % LLA according to ¹H and ¹³C NMR spectroscopies. PEO has been blended with the PVA‐g‐PLLA brush copolymer and the miscibility of the system has been analyzed by DSC, FTIR, OM, and SEM. The particular architecture of the blends results in DSC traces lacking clearly distinguishable glass transitions that have been explained considering self‐concentration effects (Lodge and McLeish) and the associated concentration fluctuations. Fortunately, the FTIR analysis is conclusive regarding the miscibility and the specific interactions in these systems. Melting point depression analysis suggests that interactions of intermediate strength and PLOM and SEM reveal homogeneous morphologies for the PEO/PVA‐g‐PLLA blends. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1217–1226     

Shape memory polymers with interconnected nanopores and high mechanical strength

The fabrication of shape memory polymers with both interconnected nanopores and high mechanical strength is challenging. In this work, porous shape memory polymers (PSMPs) were prepared based on the combination of crystallization and phase separation in a ternary blend of poly(l ‐lactic acid)/polyvinyl acetate/poly(ethylene oxide) (i.e., PLLA/PVAc/PEO). The phase separation between the PLLA and PVAc/PEO resulted in bicontinuous structures in microscale including a PLLA‐rich phase and a mixed PVAc/PEO phase. On one hand, the continuous PLLA‐rich phase contributed to the high mechanical strength and shape memory performance, in which tiny crystals and amorphous matrix of PLLA act as the shape fixed phase and reversible phase, respectively. On the other hand, the crystallization of PEO in the miscible PVAc/PEO blend produced submicrometer bicontinuous structures. The interconnected nanopores have been obtained by selective etching of the PEO. Our strategy opens a new avenue for fabricating PSMPs with both interpenetrated channels and high strength. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 125–130