Phase behavior of lyotropic rigid-chain polymer liquid crystal studied by dissipative particle dynamics

The phase behavior of lyotropic rigid-chain liquid crystal polymer was studied by dissipative particle dynamics (DPD) with variations of the solution concentration and temperature. A chain of fused DPD particles was used to represent each mesogenic polymer backbone surrounded with the strongly interacted solvent molecules. The free solvent molecules were modeled as independent DPD particles, where each particle includes a lump of solvent molecules with the volume roughly equal to the solvated polymer segment. The simulation shows that smectic-B (S(B)), smectic-A (S(A)), nematic (N), and isotropic (I) phases exist within certain regions in the temperature and concentration parameter space. The temperature-dependent S(B)∕S(A), S(A)∕N, and N∕I phase transitions occur in the high concentration range. In the intermediate concentration range, the simulation shows coexistence of the anisotropic phases and isotropic phase, where the anisotropic phases can be the S(B), S(A), or N phases. Mole fraction and compositions of the coexisted phases are determined from the simulation, which indicates that concentration of rigid rods in isotropic phase increases as the temperature increases. By fitting the orientational distribution function of the systems, the biphasic coexistence is further confirmed. From the parameter α obtained for the simulation, the distribution of the rigid rods in the two coexistence phases is quantitatively evaluated. By using model and simulation methods developed in this work, the phase diagrams of the lyotropic rigid-chain polymer liquid crystal are obtained. Incorporating the solvent particles in the DPD simulation is critical to predict the phase coexistence and obtain the phase diagrams.     

Investigation of drug release and 1H‐NMR analysis of the in situ forming systems based on poly(lactide‐co‐glycolide)

In situ forming biodegradable polymeric systems loaded with betamethasone (BTM) and betamethasone acetate (BTMA) were prepared using poly(DL ‐lactide‐co‐glycolide) (PLGA), ethyl heptanoate (EH), and N‐methyl‐2‐pyrrolidone (NMP) as the biodegradable polymer, additive, and solvent, respectively. The drug release studies were carried out in buffer (pH = 7.4, 37°C) using high performance liquid chromatography (HPLC). ¹H‐NMR was used to determine the polymer degradation behavior, release mechanism, and interactions between the polymer and drug. The ¹H‐NMR spectra showed that all interactions between the polymer and drug were hydrogen bonding. Hydroxyl groups and fluorine in drugs were involved in hydrogen bonding with PLGA polymer. In ¹H‐NMR studies, we found that the degradation rate in the systems loaded with BTMA was higher than the systems loaded with BTM because BTMA is only slightly soluble and accelerates the hydrolysis of PLGA chains. The formulations loaded with BTM had obviously lower burst release compared with BTMA loaded samples. With respect to ¹H‐NMR spectra, the mechanism of BTM release is controlled by two effective factors: solvent removal and polymer degradation. Copyright © 2008 John Wiley & Sons, Ltd.     

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     

Self‐Assembly of Imidazolium‐Based Surfactants in Magnetic Room‐Temperature Ionic Liquids: Binary Mixtures

The phase behaviour of binary mixtures of ionic surfactants (1‐alkyl‐3‐imidazolium chloride, C_nmimCl with n=14, 16 and 18) and imidazolium‐based ionic liquids (1‐alkyl‐3‐methylimidazolium tetrachloroferrate, C_nmimFeCl₄, with n=2 and 4) over a broad temperature range and the complete range of compositions is described. By using many complementary methods including differential scanning calorimetry (DSC), polarised microscopy, small‐angle neutron and X‐ray scattering (SANS/SAXS), and surface tension, the ability of this model system to support self‐assembly is described quantitatively and this behaviour is compared with common water systems. The existence of micelles swollen by the solvent can be deduced from SANS experiments and represent a possible model for aggregates, which has barely been considered for ionic‐liquid systems until now, and can be ascribed to the rather low solvophobicity of the surfactants. Our investigation shows that, in general, C_nmimCl is a rather weak amphiphile in these ionic liquids. The amphiphilic strength increases systematically with the length of the alkyl chain, as seen from the phase behaviour, the critical micelle concentration, and also the level of definition of the aggregates formed.     

Synthesis,Characterisation and Electrical Properties of Supramolecular DNA‐Templated Polymer Nanowires of 2,5‐(Bis‐2‐thienyl)‐pyrrole

Supramolecular polymer nanowires have been prepared by using DNA‐templating of 2,5‐(bis‐2‐thienyl)‐pyrrole (TPT) by oxidation with FeCl₃ in a mixed aqueous/organic solvent system. Despite the reduced capacity for strong hydrogen bonding in polyTPT compared to other systems, such as polypyrrole, the templating proceeds well. FTIR spectroscopic studies confirm that the resulting material is not a simple mixture and that the two types of polymer interact. This is indicated by shifts in bands associated with both the phosphodiester backbone and the nucleobases. XPS studies further confirm the presence of DNA and TPT, as well as dopant Cl^? ions. Molecular dynamics simulations on a [{dA₂₄:dT₂₄}/{TPT}₄] model support these findings and indicate a non‐coplanar conformation for oligoTPT over much of the trajectory. AFM studies show that the resulting nanowires typically lie in the 7–8 nm diameter range and exhibit a smooth, continuous, morphology. Studies on the electrical properties of the prepared nanowires by using a combination of scanned conductance microscopy, conductive AFM and variable temperature two‐terminal I–V measurements show, that in contrast to similar DNA/polymer systems, the conductivity is markedly reduced compared to bulk material. The temperature dependence of the conductivity shows a simple Arrhenius behaviour consistent with the hopping models developed for redox polymers.     

Dissipative Particle Dynamics Simulations of Polymer Brushes: Comparison with Molecular Dynamics Simulations

Summary: The structure of polymer brushes is investigated by dissipative particle dynamics (DPD) simulations that include explicit solvent particles. With an appropriate choice of the DPD interaction parameters , we obtain good agreement with previous molecular dynamics (MD) results where the good solvent behavior has been modeled by an effective Lennard–Jones potential. The present results confirm that DPD simulation techniques can be applied for large length scale simulations of polymer brushes. A relation between the different length scales and is established.

Polymer brush at a solid–liquid interface.     

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     

LC‐MS/MS method for simultaneous analysis of uracil, 5,6‐dihydrouracil, 5‐fluorouracil and 5‐fluoro‐5,6‐dihydrouracil in human plasma for therapeutic drug monitoring and toxicity prediction in cancer patients

The chemotherapeutic drug 5‐fluorouracil (5‐FU) is widely used for treating solid tumors. Response to 5‐FU treatment is variable with 10–30% of patients experiencing serious toxicity partly explained by reduced activity of dihydropyrimidine dehydrogenase (DPD). DPD converts endogenous uracil (U) into 5,6‐dihydrouracil (UH₂), and analogously, 5‐FU into 5‐fluoro‐5,6‐dihydrouracil (5‐FUH₂). Combined quantification of U and UH₂ with 5‐FU and 5‐FUH₂ may provide a pre‐therapeutic assessment of DPD activity and further guide drug dosing during therapy. Here, we report the development of a liquid chromatography–tandem mass spectrometry assay for simultaneous quantification of U, UH₂, 5‐FU and 5‐FUH₂ in human plasma. Samples were prepared by liquid–liquid extraction with 10:1 ethyl acetate‐2‐propanol (v/v). The evaporated samples were reconstituted in 0.1% formic acid and 10 μL aliquots were injected into the HPLC system. Analyte separation was achieved on an Atlantis dC₁₈ column with a mobile phase consisting of 1.0 mm ammonium acetate, 0.5 mm formic acid and 3.3% methanol. Positively ionized analytes were detected by multiple reaction monitoring. The analytical response was linear in the range 0.01–10 μm for U, 0.1–10 μm for UH₂, 0.1–75 μm for 5‐FU and 0.75–75 μm for 5‐FUH₂, covering the expected concentration ranges in plasma. The method was validated following the FDA guidelines and applied to clinical samples obtained from ten 5‐FU‐treated colorectal cancer patients. The present method merges the analysis of 5‐FU pharmacokinetics and DPD activity into a single assay representing a valuable tool to improve the efficacy and safety of 5‐FU‐based chemotherapy. Copyright © 2012 John Wiley & Sons, Ltd.     

Crystallization of polylactic acid under in situ deformation during nonsolvent‐induced phase separation

In this study, we investigate polylactic acid (PLA) crystallization under in situ biaxial extension in a nonsolvent‐induced phase separation foaming process. Our ternary system consists of PLA, dichloromethane (DCM) as solvent and hexane as nonsolvent. For the first time, the formation of a shish‐kebab crystalline morphology is observed in such a solution‐based foaming process in certain solid–liquid phase separated systems. The formation of shish‐kebabs is described based on the coil‐stretch transition concept. The rapid biaxial deformation caused by macropore growth uniaxially stretches the long chains that are tied with at least two single crystals which eventually leads to the formation of shish structures throughout the polymer‐rich phase. The kebab lamellae then form perpendicularly on the shish cores. The scanning electron microscopy (SEM) observations and our interpretation of the crystallization phenomena are confirmed by differential scanning calorimetry (DSC) analysis. The observation of various crystalline morphologies, particularly shish‐kebabs, and the elucidation of their formation mechanisms contribute to the understanding of phase separation and pore growth as well as crystallization in such polymer–solvent–nonsolvent systems. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1055–1062     

Computer‐Aided Estimation of Diffusion Coefficients in Non‐Solvent/Polymer Systems

A novel method for estimating the mutual and self‐diffusion coefficients of a non‐solvent/polymer system is proposed in this work. The idea is to study the evaporation process from non‐solvent/solvent/polymer systems as a one‐dimensional numerical experiment and to use polymer solution weight versus time data to fit the unknown parameters of the diffusion‐coefficient correlations based on free‐volume theory. For this purpose, the evaporation process is modeled as a coupled heat‐ and mass‐transfer problem with a moving boundary, and the Galerkin finite‐element method is used to solve simultaneously the non‐linear governing equations. This method is successfully applied to the estimation of water–cellulose acetate diffusion coefficients and is valid over the whole range of temperatures and concentrations for practical applications in membrane technology. Additionally, there is a detailed discussion on if water affects the morphology of the final cellulosic membrane by studying the concentration profiles of the constituents of the casting solution.     

Two‐dimensional liquid chromatography with active solvent modulation for studying monomer incorporation in copolymer dispersants

A pseudo‐comprehensive two‐dimensional liquid chromatography approach with size exclusion chromatography in the first dimension and gradient reversed‐phase liquid chromatography in the second dimension was successfully developed for the characterization of vinyl acetate/acrylic acid copolymers and vinyl acetate/itaconic acid/acrylic acid terpolymers. Active solvent modulation was exploited to prevent the polymer breakthrough in the second dimension separation caused by the strong solvent used in the first dimension. The conditions of the active solvent modulation valve were optimized to achieve sufficient on‐line dilution and to completely prevent polymer breakthrough without adding excessive time to the modulation cycle. Using this approach, copolymers made with different monomer ratios and processes were studied. Heterogeneous composition distribution due to insufficient monomer incorporation was detected in some of the copolymer samples. We demonstrated that with active solvent modulation, the two‐dimensional liquid chromatography approach is no longer limited to water‐soluble polymers and can be used for a broader range of polymers and copolymers.     

Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat‐panel displays, their intrinsic ability to self‐organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid‐crystalline materials as organic semiconductors, which are solvent‐processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli‐responsive macroscopic shape change of cross‐linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid‐crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.     

Isolation and purification of alkaloids from the fruits of Macleaya cordata by ionic‐liquid‐modified high‐speed counter‐current chromatography

Macleaya cordata (Willd) R. Br. is a medicinal plant. The most important bioactive compounds of M. cordata are alkaloids that have many biological activities including antifungal, anti‐inflammatory, and antitumor. In this study, an ionic‐liquid‐modified high‐speed counter‐current chromatography method was established to obtain alkaloids from the fruits of M. cordata. The conditions of ionic‐liquid‐modified high‐speed counter‐current chromatography, including solvent systems, the content of ionic liquid (1‐butyl‐3‐methylimidazolium tetrafluoroborate [C₄mim][BF₄]), and the posttreatment of the ionic liquid, were investigated. Five alkaloids protopine, allocryptopine, sanguinarine, 8‐O‐demethylchelerythrine, and chelerythrine were separated from the extract of the fruits using a high speed counter‐current chromatography with two‐phase solvent system composed of dichloromethane/methanol/0.3 mol/L hydrochloric acid aqueous solution/[C₄mim][BF₄] (4:2:2:0.015, v/v). Their purities were 96.33, 95.56, 97.94, 96.22, and 97.90%, respectively. The results indicated that a small amount of ionic liquids as modifier of the two‐phase solvent system could shorten the separation time and improve the separation efficiency of the alkaloids from the fruits. The ionic‐liquid‐modified high‐speed counter‐current chromatography would provide a feasible way for highly effective separation of alkaloids from natural products.     

Separation of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane and 1,3,5‐trinitro‐1,3,5‐ triazacyclohexane by molecularly imprinted solid‐phase extraction

Synthesis of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane and 1,3,5‐trinitro‐1,3,5‐triazacyclohexane by the Bachmann process leads to a mixture of both. The separation of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane and 1,3,5‐trinitro‐1,3,5‐triazacyclohexane from their mixture is difficult because the sizes and physical properties of these homologous compounds are similar. For this purpose, seven molecularly imprinted polymers have been synthesized for each explosive, and a selective solid‐phase extraction procedure has been developed. A molecularly imprinted polymer, synthesized with 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane as the template, methacrylic acid as the monomer and trimethylolpropane trimethacrylate as the cross‐linking agent in a molar ratio of 1:8:8 showed the best separation capability. A packed cartridge containing this polymer can be reused for 23 solid‐phase extraction cycles without repacking, and the total separation capability toward 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane reached 6.81 mg per gram of polymer. 1,3,5‐Trinitro‐1,3,5‐triazacyclohexane was not detected in the separated 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane by high‐performance liquid chromatography and vice versa. This newly developed method had the advantages of high recovery (100%) and purity, environmental friendliness, and room temperature operability. This study showed that some molecularly imprinted polymers that cannot absorb target analytes well in the solvent in which the polymers were polymerized might have high‐binding capacity for the analytes and show imprinting effects in other solvents.     

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.     

Enhanced electrochemical response of solution‐deposited n‐doping polymer via cocasting with ionic liquid

A novel cocasting approach is presented for improving electroactivity of solution‐cast films of conducting polymers. Solutions of the n‐doping polymer poly(benzimidazobenzophenanthroline) (BBL) were co‐deposited with the ionic liquid electrolyte 1‐ethyl‐3‐methyl‐imidazolium bis(trifluoromethylsulfonyl)imide (EMIBTI). The resultant co‐continuous mixture yielded highly porous polymer films (CC‐BBL) upon removal of solvent and EMIBTI. Electrochemical quartz crystal microgravimetry revealed that the n‐doping process in neat ionic liquid is anion‐dominant, which is contrary to what is observed in dilute electrolyte solutions. The CC‐BBL films exhibit a thirty‐fold increase in initial current response and capacity relative to non‐cocast BBL films. While current response and capacity of the non‐cocast BBL improve with cycling, they level out after 800 cycles at 35% of those of the CC‐BBL. CC‐BBL shows high n‐doping stability; no decrease in electroactivity is seen after 1000 cycles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Solvent‐Induced Helical Assembly and Reversible Chiroptical Switching of Chiral Cyclic‐Dipeptide‐Functionalized Naphthalenediimides

Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self‐assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary‐functionalized naphthalenediimides (NCDPs 1 – 6 ) have been prepared and their chiral self‐assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1 – 3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M‐ to P‐type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid‐state thin‐film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4 – 6 ), with an achiral or D ‐isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π–π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P‐) and left (M‐) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent‐induced helical assembly and reversible chiroptical switching of naphthalenediimides.     

The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.     

Deep‐Eutectic‐Solvent‐Based Self‐Healing Polymer Electrolyte for Safe and Long‐Life Lithium‐Metal Batteries

The deployment of high‐energy‐density lithium‐metal batteries has been greatly impeded by Li dendrite growth and safety concerns originating from flammable liquid electrolytes. Herein, we report a stable quasi‐solid‐state Li metal battery with a deep eutectic solvent (DES)‐based self‐healing polymer (DSP) electrolyte. This electrolyte was fabricated in a facile manner by in situ copolymerization of 2‐(3‐(6‐methyl‐4‐oxo‐1,4‐dihydropyrimidin‐2‐yl)ureido)ethyl methacrylate (UPyMA) and pentaerythritol tetraacrylate (PETEA) monomers in a DES‐based electrolyte containing fluoroethylene carbonate (FEC) as an additive. The well‐designed DSP electrolyte simultaneously possesses non‐flammability, high ionic conductivity and electrochemical stability, and dendrite‐free Li plating. When applied in Li metal batteries with a LiMn₂O₄ cathode, the DSP electrolyte effectively suppressed manganese dissolution from the cathode and enabled high‐capacity and a long lifespan at room and elevated temperatures.