Permeation of a solvent mixture through an elastomeric membrane—The case of pervaporation

This article presents a model for the permeation of solvent mixtures through an elastomer in the particular case of pervaporation. An analytical expression for each solvent permeation rate is derived, in the limited case of a membrane that undergoes small swelling, without making any assumptions on the solvent diffusion coefficients and their dependence on solvent concentrations. Applying this analytical expression to different situations, we fitted most of the curves previously published on pervaporation experiments. In particular, we correlated the synergy developed by a mixture of two solvents in the permeation process with the sign of their Flory–Huggins interaction parameter χ_AB. This explains why, in most cases (χ_AB > 0), a molecule permeating easily through a membrane is mixed with a molecule permeating much less easily; the latter can see its permeation flux increase by a factor 10 or 100 because the swelling of the polymer induced by the more permeable molecule “opens the meshes of the network” allowing the less permeable molecule to pass through more easily. Within our analysis, the efficiency of the pervaporation process, expressed through the separation factor, is derived very simply as a function of the interaction coefficients and the viscosities of solvents and exhibits an exponential dependence on the volume fraction of either component as seen in most experiments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 183–193, 2003     

Monolayer and multilayer compact film formations on different substrates by physical deposition

Dissipative particle dynamics simulations are applied to investigate the monolayer and multilayer film formations on different solid substrates by physical deposition. The influences of the polymer concentration, the polymer chain length, the solvent quality, and the interactions between the polymer solution and the solid substrate surface on the film formation dynamics and the mechanism are studied in detail. The results are analyzed in terms of the thickness and the shape of the deposited film, the kinetics of phase separation in the polymer solution, and the contact angle formed between the polymer aggregations and the substrate surface. Moreover, we suggest two strategies, designing a deposition process analogous to “chemical titration” and physically blocking interlayer diffusion by a simple crosslinked network barrier, to deposit the compact monolayer and multilayer films with better quality, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 353–365, 2009     

Investigation of dipole alignments by swelling in poled thin films of a side-group polymer using second harmonic generation

This paper deals with relations between solvent diffusion and changes in second harmonic generation (SHG) in a side-group polymer with nonlinear optical (NLO) chromophores. The SHG signal of poled polymer thin films was measured as a function of time during the swelling process with methanol. The results indicated that the diffusion process was Fickian. The topographic results obtained by atomic force microscopy, together with the SHG data, also demonstrated the existence of the domain layer formed during poling that gave rise to the principal SHG intensity for this sample. Also, a noncentrosymmetric chromophore ordering was induced by swelling in the absence of a poling electric field. This time-varying SHG signal upon swelling was discussed in terms of dipolar and polar alignments of the side-group NLO chromophores. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3108–3114, 1999     

Swelling equilibrium and sorption kinetics of urethane-modified bismaleimides elastomer

The swelling equilibrium and diffusion kinetics in various solvents of the maleimide-terminated polyurethanes (UBMIs) and of the triol and tetraol-crosslinked polyurethanes (PU) were studied. The polymer volume fraction of the UBMIs at swelling equilibrium is much higher than that of the tetraol-crosslinked PU networks for the same type of polyol used in the PU. It was explained by the high functionality of the UBMIs produced in the network structure. Furthermore, the molecular weight between crosslinks (M_c) has been calculated from the swelling model and the results exhibit good agreement with the proposed network structure. The early time sorption kinetic data were obtained to investigate the diffusion mechanism of the solvent in the networks. The solubility, diffusion coefficients, and permeability of the solvent in UBMI networks were found to be lower than in the multiol-crosslinked PU networks. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1747–1755, 1997     

Click chemistry in materials synthesis. II. Acid‐swellable crosslinked polymers made by copper‐catalyzed azide–alkyne cycloaddition

A highly crosslinked hyperbranched polymer that rapidly swells and shrinks in a halogenated solvent in response to the addition of an acid or base has been prepared by Cu(I) catalysis of the reaction between a diazide and an amine‐containing trialkyne. The triazole linkages in the polymer are highly stable and may also play a role in the swelling behavior. The swelling–deswelling process is reversible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5513–5518, 2006     

A Monte Carlo study of the coil-to-globule transition of model polymer chains near an attractive surface

When a polymer chain in solution interacts with an atomically smooth solid substrate, its conformational properties are strongly modified and deviate substantially from those of chains in bulk. In this work, the interplay of two competing transitions that affect the conformations of polymer chains near an energetically attractive surface is studied by means of Monte Carlo simulations on a cubic lattice. The transition from an extended to a compact conformation of a polymer chain near an attractive wall, as solubility deteriorates, exhibits characteristics akin to the “coil-to-globule” transition in bulk. An effective θ-temperature is determined. Its role as the transition point is confirmed in a variety of ways. The nature of the coil-to-compact transition is not qualitatively different from that in the bulk. Adsorbed polymer chains may assume “globular” or “pancake” configurations depending on the competition among adsorption strength, cohesive energy, and entropy. In a very relevant range of conditions, the dependence of the adsorbate thickness on chain-length is intermediate between that of 3-d (“semidroplets”) and 2-d (“pancake”) objects. The focus of this study is on rather long polymer chains. Several crucial features of the transitions of the adsorbed chains are N-dependent and various aspects of the adsorption and “dissolution” process are manifested clearly only at the “long chain” limit. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2462–2476, 2009     

On the nature of phase separation of polymer solutions at high extension rates

Experiments with stretching moderately concentrated polymer solutions have been carried out. Model experiments were carried out for poly(acrylonitrile) solutions in dimethyl siloxane. Just the choice of concentrated solutions allowed for a clear demonstration of a demixing effect with the formation of two separate phases—an oriented polymer fiber and solvent drops sitting on its surface. An original experimental device for following all subsequent stages in the demixing process was built. It combined two light beams, one transverse to the fiber and a second directed along (inside) the fiber, the latter played the role of an optical line. This gives a unique opportunity to observe processes occurring inside a fiber. The process of demixing starts from the volume phase separation across the whole cross section of a fiber at some critical deformation and the propagation of the front of demixing along the fiber. Then a solvent cylindrical skin appears which transforms into a system of separate droplets. New experimental data are discussed based on a comparison of the current different points of view on the phenomenon of deformation‐induced phase separation: thermodynamic shift of the equilibrium phase transition temperature, growth of stress‐induced concentration fluctuations in two‐component fluids, and mechanically pressing a solvent out from a polymer network. The general belief is that a rather specific (so‐called “beads‐on‐a‐string”) structure of a filament is realized in stretching dilute solutions: beads of a polymer solution connected by oriented polymer bridges forming a single object. The situation in stretching moderately concentrated solutions appears quite different: real phase separation was observed. So, the alternative phenomenon to the formation of the “beads‐on‐a‐string” structure has been experimentally proven. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 559–565     

Effects of structural imperfections on the dynamic mechanical response of main-chain smectic elastomers

We examine the influence of structural imperfections on mechanical damping in polydomain smectic main-chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan δ = G″(ω)/G′(ω) exhibits a strong maximum (tan δ ≈ 1.0) near the smectic-isotropic (clearing) transition. “Optimal” elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling “imperfect elastomers” that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan δ is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan δ and its temperature dependence are similar for optimal and imperfect elastomers at ω = 1 Hz. The prominent loss peak near the clearing transition arises from segment-level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration-damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3267–3276, 2007     

Effects of repeated water exchange on the swelling behavior of poly(sodium acrylate) gels crosslinked by aluminum ions

Polyelectrolyte hydrogels, physically crosslinked by metal ions, were synthesized using poly(sodium acrylate) as the main constituent and Al ions as the crosslinker. The swelling ratio of the gel was measured whenever the solvent water was repeatedly exchanged in a constant interval. The as‐synthesized gel exhibited two relaxation processes; the gel swelled at the first stage, then shrunk very slowly at the second stage, and recovered to the initial size just after the gelation (ultimately, the gel became smaller than that). The relaxation times of both processes were found longer (exceptionally longer for the shrinking process) than the conventional collective diffusion of polymer networks. The diffused amounts of Al ions and Na counter ions in the solvent were also measured at each water exchange. The diffusion of Al ions into the solvent was found to finish when the swelling ratio took the maximum (at the end of the first stage), while Na ions continued to diffuse until the diameter became the final one (at the end of the second stage). The microscopic structural changes by the repeated water exchange were obtained by the measurements of ATR FT‐IR spectroscopy on the gels with different swelling ratios. The carboxyl groups were gradually protonated on both stages, and the formation of hydrogen bonding was accelerated on the second stage. Effects of the repeated water exchange on the swelling behavior are discussed in terms of the diffusion of Al ions into the solvent, the exchange of Na counter ions by protons, and the formation of hydrogen bonding. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 753–763, 2005     

STRUCTURING ＆ RHEOLOGY OF MOLTEN POLYMER／CLAY NANOCOMPOSITES

The evolution and the origin of “solid-like state” in molten polymer/clay nanocomposites are studied. Using polypropylene/clay hybrid (PPCH) with sufficient maleic anhydride modified PP (PP-MA) as compatibilizer, well exfoliation yet solid-like state was achieved after annealing in molten state. Comprehensive linear viscoelasticity and non-linear rheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the “solid-like” state in molten nanocomposites. Based on these, it is revealed that the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets, the formation of band/chain structure and, finally, a percolated clay associated network, which is responsible for the melt rigidity or solid-like state. The network will be broken down by melt frozen/crystallization and weakened at large shear or strong flow and, even more surprisingly, may be disrupted by using trace amount of silane coupling agent which may block the edge interaction of platelets. The solid-like structure causes characteristic non-linear rheological behaviors, e.g. residual stress after step shear, abnormal huge stress overshoots in step flows and, most remarkably, the negative first normal stress functions in steady shear or step flows. The rheological and structural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chains connecting clay particles or by chains in confined melts or frictional interaction among tactoids. A scheme of percolated networking of associated clay platelets, which may in band form of edge connecting exfoliated platelets, is suggested to explain previous experimental results.     

Sensing of liquids by electrically conductive immiscible polypropylene/thermoplastic polyurethane blends containing carbon black

Immiscible polymer blends based on polypropylene/thermoplastic polyurethane (PP/TPU) are interesting host multiphase systems for the incorporation of low concentrations of conductive carbon black (CB) particles. The enhancement of conductivity (and the lower critical CB content for percolation) in the PP/TPU blend is achieved via double percolation, that is, structural and electrical. The CB particles form chainlike network structures within the TPU phase, which exhibit phase continuity of elongated particles within the PP matrix. Moreover, scanning electron microscopy and dynamic mechanical thermal analysis studies indicated that the incorporation of CB particles into the PP/TPU blend has a “compatibilizing” effect, resulting in an enhanced interaction between the two polymers. Extruded PP/TPU/CB filaments produced by a capillary rheometer process at various shear rates were examined as sensing materials for a homologous series of alcohols, that is, methanol, ethanol, and 1‐propanol. All filaments displayed increasing resistance upon exposure to the various alcohols combined with excellent reproducibility and recovery behavior. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB‐containing immiscible polymer blend characterized by a double‐continuity structure. The interphase region, its quantity, and continuity played a significant role in the liquid‐transport process. Blend composition, filaments' extrusion temperature, and production shear rate level were considered as significant parameters determining the structure and the resultant sensing properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1428–1440, 2003     

Investigation of swelling and diffusion in polymers by NMR imaging

The kinetics of diffusion in polymers ranges from simple Fickian diffusion to higher order diffusion, such as Case II diffusion^1-2). The conventional method for determining the characteristics of solvents into polymer matrices is by measuring the mass uptake of the polymer as the solvent penetrates the matrix. However, since such measurements perform observations at a macroscopic level, little information has been obtained relating to the nature of the solvent in the polymer matrix and the mechanisms of the processes that control the diffusion. Nuclear magnetic resonance (NMR) imaging (‘MRI’) has been used to observe the penetration of solvents into solid systems in realtime. The method provides a one- or more-dimensional image of the density and the mobility of the solvent in a material or of the network changes of the material itself due to the softening influence of the solvent. The first (imaging of the solvent) can be used for a quantitative measurement of the diffusion whereas the observation of the network gives information about the changing of the network (mobility, de-crystallization…) during the swelling process. For example the diffusion of organic solvents in some polymeric materials (natural rubber, water gels (PNIPAAm), and nematic diblock-copolymers) are investigated.     

Polymer dynamics in hydrogenous systems by neutron reflectivity

Neutron reflectivity is a powerful tool for exploring polymer dynamics above the glass-transition temperature at short diffusion times in layered thin-film systems. Recent studies of membrane-mediated interdiffusion in deuterium-labeled systems have shown that ultrathin membranes can track the position of the interface in binary polymeric diffusion couples and also can discriminate between perdeuterated and hydrogenous polymers of the same molecular weight. This report shows that similar dynamic information can be obtained for binary hydrogenous polystyrene (hPS) diffusion couples separated by an ultrathin (6-nm) isopentylcellulose cinnamate (IPCC) membrane on Si wafers (air//hPS/IPCC/hPS//Si, where “//” represents an interface between obviously different phases and “/” represents a dynamic interface between polymeric species). In particular, the air//hPS/IPCC/hPS//Si system provides the same information as perdeuterium-labeled polystyrene (dPS) diffusion couples separated by the same IPCC membrane (air//dPS/IPCC/dPS//Si). This technique has potential applications for the study of confinement effects on thin-film dynamics and macromolecular transport across membranes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3248–3257, 2004     

Rapid synthesis of poly(HPA‐co‐VeoVa 10) amphiphilic gels toward removal of toxic solvents via plasma‐ignited frontal polymerization

Atmospheric air plasma was created and applied in the frontal polymerization (FP) of fabricating poly(HPA‐co‐VeoVa 10) amphiphilic gels (HPA = 2‐hydroxypropyl acrylate, VeoVa 10 = vinyl versatate) with enhanced physicochemical properties. In plasma‐ignited frontal polymerization (PIFP), once ignited by air plasma, no further energy or treatment was required for the following polymerization. In this system, the comparison between PIFP and thermal frontal polymerization (TFP) was conducted and observed that PIFP and TFP differ considerably in terms of swelling capacity, morphology and component distribution of the products. This finding is of great importance that the simultaneous generation of active radicals in the initial stage can spread throughout reactant and anchor on the synthetic polymer with the assistance of FP. More interestingly, the PIFP‐synthesized copolymer possesses remarkable selective absorption towards organic solvents, which can be facilely manipulated by varying the weight ratios of HPA/VeoVa 10. Obviously, these polymer products could serve as an “organic solvent scavenger” in the field of industrial wastewater treatment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Measurement of concentration gradients in swelling crosslinked polymer beads

The concentration of solvent in the gel phase of a swelling polystyrene–divinylbenzene copolymer bead has been measured as a function of the radius by optical interference techniques. It is found that an appreciable gradient exists even shortly after the core disappears. Results are presented for two cases: a very lightly crosslinked bead that exhibits negligible birefringence while swelling, and a more tightly crosslinked network in which the birefringence must be considered. It is also found that the refractive index of the unswollen bead is considerably less than that found by extrapolation from the swollen state; this effect is reasonable when the “free volume” in the bulk polymer is considered.     

Mechanism of plasma-initiated polymerization: Concerning the nature of solvent effects on the lifelike polymerization of water-soluble vinyl monomers

To provide a satisfactory basic understanding of the solvent effect of plasma-initiated polymerization, we have carried out several kinds of polymerizations of various water-soluble vinyl monomers. It has been shown that aqueous solution of such vinyl monomers underwent the polymerizations induced by methyl isobutyrate (MIB) plasma-exposed glass surface. The invisible ultrathin polymer film trapping an active radical species deposited on the plasma-exposed glass surface apparently induced the polymerizations. The efficiency, however, was largely dependent on the solvent used: the solvent can be considered to act as “an initiation-activator” for the lifelike postpolymerization. The nature of the solvent effect was ascribed to the physicomechanical property such as swelling ability and/or solubility toward the ultrathin film formed on the glass surface. Thus it has been suggested that the choice of good-balanced combination between the structural feature of the plasma-induced ultrathin polymer film and the solvent as an initiation-activator is important to achieve activity of a desired solution polymerization.     

Hydrogen-bonded supramolecular polymer networks

The strong dimerizing, quadruple hydrogen-bonding ureido-pyrimidone unit is used to obtain reversible polymer networks. A new synthetic route from commercially available starting materials is described. The hydrogen-bonding ureido-pyrimidone network is prepared using 3(4)-isocyanatomethyl-1-methylcyclohexyl-isocyanate (IMCI) in the regioselective coupling reaction of multi-hydroxy functionalized polymers with isocytosines. ¹H- and ¹³C-NMR, IR, MS, and ES-MS analysis, performed on a model reaction using butanol, demonstrated the formation of the hydrogen-bonding ureido-pyrimidone unit in a yield of more than 95%. The well-defined, strong hydrogen-bonding ureido-pyrimidone network is compared with a traditional covalently bonded polymer network, a multi-directional hydrogen-bonded polymer network based on urea units, and a reference compound. The advantage of the reversible, hydrogen-bonded polymer networks is the formation of the thermodynamically most favorable products, which show a higher “virtual” molecular weight and shear modulus, compared to the irreversible, covalently bonded polymer network. The properties of the ureido-pyrimidone network are unique; the well-defined and strong dimerization of the ureido-pyrimidone unit does not require any additional stabilization such as crystallization or other kinds of phase separation, and displays a well-defined viscoelastic transition. The ureido-pyrimidone network represents the first example of a truly reversible polymer network showing these features. Furthermore, the ureido-pyrimidone dimerization is strong enough to construct supramolecular materials possessing acceptable mechanical properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3657–3670, 1999     

Novel amphiphilic network polymers consisting of nonpolar,short primary polymer chains and polar,long crosslink units: Influence of characteristic dangling chains on swelling behavior of resulting amphiphilic gels

Novel amphiphilic network polymers consisting of nonpolar, short primary polymer chains and polar, long crosslink units were prepared, and the swelling behavior of resulting amphiphilic gels is discussed by focusing on the influence of characteristic dangling chains; that is, benzyl methacrylate (BzMA) was copolymerized with tricosaethylene glycol dimethacrylate [CH₂?C(CH₃)CO(OCH₂CH₂)₂₃OCOC(CH₃)?CH₂, PEGDMA‐23] in the presence of lauryl mercaptan as a chain‐transfer agent because BzMA forms nonpolar, short primary polymer chains and PEGDMA‐23 as a crosslinker contains a polar, long poly(oxyethylene) unit. The enhanced incorporation of dangling chains into the network polymer was brought by shortening the primary polymer chain length, and copolymerization with methoxytricosaethylene glycol methacrylate, a mono‐ene counterpart of PEGDMA‐23, enforced the incorporation of flexible dangling poly(oxyethylene) chains into the network polymer, although the former dangling chains as terminal parts of primary poly(BzMA) chains were rather rigid. Then, the influence of characteristic dangling chains on the swelling behavior of amphiphilic gels was examined in mixed solvents consisting of nonpolar t‐butylbenzene and polar methanol. The profiles of the solvent‐component dependencies of the swelling ratios were characteristic of amphiphilic gels. The introduction of dangling poly(oxyethylene) chains led not only to an increased swelling ratio but also to sharpened swelling behavior of amphiphilic gels. The swelling response of amphiphilic gels was checked by changing the external solvent polarity. The dangling chains with freely mobile end segments influenced the swelling response of gels. The amphiphilic gels with less entangled, collapsed crosslink units exhibited faster swelling response than the ones with more entangled, collapsed primary polymer chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2192–2201, 2004     

Formation of porous polymer morphology by microsyneresis during divinylbenzene polymerization

This article describes the investigation of the importance of various reaction conditions on microsyneretic pore formation during polymerization of divinylbenzene (DVB) under so‐called “solvothermal” conditions. To induce microsyneretic pore formation, the most important parameter is an unusually high dilution of monomers with a “good” porogen solvating the polymer chains. High dilution and solvation of the growing poly(DVB) chains promote the prolongation of the polymer chains rather than their interconnection by crosslinking. Consequently, when the polymer gel density reaches the point where syneresis starts, the polymer network is geometrically too extensive to be broken up into precipitating entities and, instead, porogen droplets are formed within the continuous polymer gel. The pore geometry created by microsyneresis offers high surface area in wide mesopores and hence, high capacity for supporting functional groups or reactions with much better accessibility than narrow pores between polymer microspheres produced by macrosyneresis in conventional styrenic polymer supports. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 774–781     

Advances in smart materials: Stimuli-responsive hydrogel thin films

This review highlights recent developments in the field of stimuli-responsive hydrogels, focusing primarily on thin films, with a thickness range between 100 nm to 10 μm. The theory and dynamics of hydrogel swelling is reviewed, followed by specific applications. Gels are classified based on the active stimulus—mechanical, chemical, pH, heat, and light—and fabrication methods, design constraints, and novel stimuli-responses are discussed. Often, these materials display large physiochemical reactions to a relatively small stimulus. Noteworthy materials larger than 10 μm, but with response times on the order of seconds to minutes are also discussed. Hydrogels have the potential to advance the fields of medicine and polymer science as useful substrates for “smart” devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1084–1099