Solution Temperature Type Phase Behavior Research Articles

Applicability of the Generalized Stokes-Einstein Equation of Mode-Coupling Theory to Near-Critical Polyelectrolyte Complex Solutions.

We examine whether the mode-coupling theory of Kawasaki and Ferrell (KF) [Kawasaki, K. Kinetic Equations and Time Correlation Functions of Critical Fluctuations. Ann. Phys. 1970, 61 (1), 1-56; Ferrell, R. A. Decoupled-Mode Dynamical Scaling Theory of the Binary-Liquid Phase Transition. Phys. Rev. Lett. 1970, 24 (21), 1169-1172] can describe dynamic light scattering (DLS) measurements of the dynamic structure factor of near-critical polyelectrolyte complex (PC) solutions that have been previously shown to exhibit a theoretically unanticipated lower critical solution temperature type phase behavior, i.e., phase separation upon heating, and a conventional pattern of static critical properties (low angle scattering intensity and static correlation, ξs) as a function of reduced temperature. Good qualitative accord is observed between our DLS measurements and the KF theory. In particular, we observe that the collective diffusion coefficient Dc of the PC solutions obeys the generalized Stokes-Einstein equation (GSE), Dc = kBT/6πηξs, where ξs is specified from our previous measurements and where η is measured by capillary rheometry under the same thermodynamic conditions as in our previous study of these solutions, allowing for a no-free-parameter test of the GSE. We also find that even the wavevector (q)-dependent collective diffusion coefficient Dc(q), measured by varying the scattering angle in the DLS measurements over a large range, is also well-described by the mean-field version of the KF theory. We find it remarkable that the KF theory provides such a robust description of collective diffusion in these complex charged polyelectrolyte blends under near-critical conditions given that charge fluctuations and association of the polymers might be expected to lead to physical complications that would invalidate the standard model of uncharged fluid mixtures.

새로운 BET 희석제를 이용한 고다공성 폴리에틸렌 분리막 제조

Polyethylene (PE) membranes having various porosities are used as microfilters and separators in lithium ion batteries. Membranes having a high porosity are required for use as separators in a large scale lithium ion secondary battery. In this study, BET was examined for use as a new nontoxic diluent for the fabrication of highly porous PE membranes by thermally induced phase separation process. It was confirmed that BET can be used as a new diluent for the fabrication of the PE membranes by exploring upper critical solution temperature type phase behavior of PE mixtures with BET. When the porosity of the membrane prepared from the PE/PO mixture was compared with that prepared from PE/BET mixture, the latter was about 1.8 times higher than the former.

Effects of the diluent mixing ratio and conditions of the thermally induced phase‐separation process on the pore size of microporous polyethylene membranes

AbstractMicroporous polyethylene (PE) membranes having a controlled pore size were produced via the thermally induced phase separation process by manipulation of the phase boundary of the PE/diluent blend and process conditions. The phase boundary of the PE blend, caused by upper critical solution temperature type phase behavior, was controlled by the use of a diluent mixture, that is, an isoparaffin/soybean oil mixture. The phase‐separation temperature of the PE/soybean oil blend was always higher than that of the PE/isoparaffin blend. In PE/(isoparaffin/soybean oil) ternary blends, the phase‐separation temperature of the ternary blend rapidly increased with increasing soybean oil content in the diluent mixture. Furthermore, the phase‐separation temperatures of ternary blends were always higher than that of the PE/soybean oil blend, regardless of the blend compositions, when the diluent mixture contained more than 50 wt % soybean oil. The observed phase behavior of the ternary blends was analyzed with interaction energy densities calculated with the Flory–Huggins theory and ternary stability conditions. The growth of droplets caused by both coalescence and the Oswald ripening process was observed after the onset of phase separation. As the blends became less stable, the droplet growth rate increased, and larger equilibrium droplets were formed. Microporous membranes with the desired pore structure could be prepared by control of the phase boundary and the variation of processing conditions such as the quenching depth, annealing time, and cooling rate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Upper critical solution temperature type phase behavior of poly(styrene-co-acrylonitrile) blends with poly(styrene-co-n-phenyl maleimide) and their interaction energies

To enhance the heat resistance of poly(styrene-co-acrylonitrile-co-butadiene), ABS, miscibility of poly(styrene-co-acrylonitrile), SAN, with poly(styrene-co-n-phenyl maleimide), SNPMI, having a higher glass transition temperature than SAN was explored. SAN/SNPMI blends casted from solvent were immiscible regardless of copolymer compositions. However, SNPMI copolymer forms homogeneous mixtures with SAN copolymer within specific ranges of copolymer composition upon heating caused by upper critical solution temperature, UCST, type phase behavior. Since immiscibility of solvent casting samples can be driven by solvent effects even though SAN/SNPMI blends are miscible, UCST-type phase behavior was confirmed by exploring phase reversibility. When copolymer composition of SNPMI was fixed, the phase homogenization temperature of SAN/SNPMI blends was increased as AN content in SAN copolymer increased. To understand the observed phase behavior of SAN/ SNPMI blend, interaction energies of blends were calculated from the UCST-type phase boundaries by using the lattice-fluid theory combined with a binary interaction model.

Polycarbonate/Copolyester Blends Having Optical-Grade Clarity and Their Upper Critical Solution Temperature Type Phase Behavior

The miscibility of bisphenol A polycarbonate (PC) and poly(ethylene terephthalate−co−1,4-dimethyl cyclohexane terephthalate) copolyesters (PECT) containing various amount of 1,4-dimethyl cyclohexane were explored to produce a blend having optical-grade clarity. It is known that PC does not form miscible blends with poly(ethylene−terephthalate) (PET), while it forms a miscible blend with poly(1,4-dimethyl cyclohexane terephthalate) (PCT). PC blends with PECT copolyesters prepared by solvent casting were not miscible regardless of the copolyester composition. However, PC and PECT copolyesters containing 1,4-dimethyl cyclohexane from 32 to 80 mol % formed homogeneous mixtures upon heating. Since immiscibility of solvent casting samples can be driven by solvent effects even though PC/PECT binary blends are miscible, upper critical solution temperature (UCST) type phase behavior was confirmed by exploring phase reversibility. The phase homogenizing temperature of PC/PECT blends exhibiting UCST-type phase behav...

Novel Miscible Blends Composed of Poly(ether sulfone) and Poly(1-vinylpyrrolidone-co-styrene) Copolymers and Their Interaction Energies

The miscibility of poly(ether sulfone), PES, with various hydrophilic copolymers containing 1-vinylpyrrolidone or vinyl alcohol as a repeat unit was explored. Among these blends, PES formed homogeneous mixtures with poly(1-vinylpyrrolidone-co-styrene) copolymers, P(VP-S), containing VP from 59 to 92 wt %. Miscible PES blends with P(VP-S) copolymers underwent phase separation on heating caused by lower critical solution temperature type phase behavior. The phase separation temperature of miscible blends first increases gradually with VP content, goes through a broad maximum centered at about 77 wt % VP, and then decreases just prior to the limiting content of VP for miscibility with PES. The calculated interaction energies of PES/P(VP-S) blends indicated that miscibility of these blends stemmed from the intramolecular repulsion between VP and styrene.

Interaction energies for blends based on glycidyl methacrylate copolymers

The phase behaviour of blends of glycidyl methacrylate/methyl methacrylate (GMA/MMA) copolymers with styrene/acrylonitrile (SAN) copolymers and of GMA/styrene copolymers with tetramethyl polycarbonate and poly(2,6-dimethyl-1,4-phenylene oxide) has been determined and analysed using two theoretical approaches. Binary interaction densities for repeat-unit pairs were evaluated from the lower critical solution temperature type phase behaviour using the lattice-fluid theory of Sanchez and Lacombe and from copolymer composition miscibility boundaries using the Flory-Huggins theory. For the GMA/MMA-SAN system the interaction energies obtained by the two approaches agree quite well with each other and with independent information obtained by the critical molecular-weight method.

Miscibility and lower critical solution temperature type phase behavior of poly(ethyl acrylate)/poly(vinylidene fluoride-cohexafluoro acetone) blends

The miscibility of mixtures of poly(ethyl acrylate) (PEA) with poly (vinylidene fluoride-co-hexafluoro acetone) (P(VDF-HFA)) was investigated with optical microscopy and differential scanning calorimetry (DSC). In PEA/P(VDF-HFA) blends with P(VDF-HFA) content of 50 and 70(wt%), the heterogeneous phase morphology was observed on optical micrographs at 210°C. It was found that PEA/P(VDF-HFA) blends showed the lower critical solution temperature type (LCST) phase behavior. The endothermic peak for PEA / P(VDF-HFA) blend observed on DSC thermogram near 200°C corresponded to the liquid-liquid phase transition temperature as shown in the heterogeneous phase morphology with optical microscopy. It was expected that the endothermic peak is the transition temperature from miscibility to immiscibility.