Thermodynamic analysis on the cononsolvency of poly (vinyl alcohol) in water–DMSO mixtures through the ternary interaction parameter

Isothermal phase diagrams for the semicrystalline poly (vinyl alcohol) (PVA) in solutions composed of water and dimethylsulfoxide (DMSO) was studied at 25 °C. From the observed phase behavior, PVA was soluble in either water or DMSO individually but crystallization-induced gelation and liquid–liquid demixing were observed in water–DMSO mixtures. Flory–Huggins formalism including three binary interaction parameters and one ternary interaction parameter was used to study the phenomenon of the cononsolvency, i.e. the formation of nonsolvents by mixing two solvents. The equilibrium crystallization line in the DMSO-rich region and the total calculated binodals agreed well with the measured results when a composition-dependent ternary interaction parameter was included into calculations. In contrast, calculations yielded crystallization-induced gelation in the water-rich region, but experiments indicated that PVA remained well dissolved even 1 year after preparation. The discrepancy was explained by the temperature-induced changes in the relative interaction between water and PVA. In addition, the role of the ternary interaction parameter in the cononsolvent ternary polymer systems was discussed. It was found the contribution of the ternary interaction parameter in the cononsolvent system under study is to decline the degree of the cononsolvency. The driving force for cononsolvency is the strong interaction between water and DMSO to form the stable DMSO hydrate to exclude PVA segments in the vicinity of the hydrate.     

Correlation of thermodynamic modeling and molecular simulations for liquid-liquid equilibrium of ternary polymer mixtures based on a phenomenological scaling method

In our previous study [S.Y. Oh, Y.C. Bae, J. Phys. Chem. B 114 (2010) 8948-8953], we presented a new method to predict liquid-liquid equilibria in ternary simple liquid mixtures by using a combination of a thermodynamic model and molecular simulations. As a continuation of that effort, we extend our previously developed method to ternary polymer systems. In the simulations, we used the dummy atoms to calculate the pair interaction energy values between the polymer segments and the solvent molecules. Furthermore, a thermodynamic model scaling concept is introduced to consider the chain length dependence of the energy parameters. This method was applied to ternary mixtures incorporating low to high molecular weight polymers. The method presented here well described the experimental observations using one or no adjustable parameters.     

分子量多分散性对AB二嵌段共聚物相行为的影响

采用Monte Carlo方法研究了分子量多分散性对AB型嵌段共聚物相行为的影响. 通过调整嵌段共聚物中组分含量, 考察了整体多分散性和单嵌段多分散性对嵌段共聚物共混物的有序-无序转变(Order-disorder transition, ODT)、 形貌及链尺寸的影响. 研究结果表明, 多分散度的增大使无序相向较大χN区域略微移动, 形成的片层结构厚度增加. 在形成微观有序形貌后, 较大分散度时各亚组分的链会得到更大的伸展, 表明分子链堆积受挫的程度减小, 因此, 涨落作用受到的抑制作用减小, 无序相区向更低温度区域移动.     

Phase behavior of ternary mixtures {aliphatic hydrocarbon + aromatic hydrocarbon + ionic liquid}: Experimental LLE data and their modeling by COSMO-RS

Separation of aromatic and aliphatic hydrocarbons is a complex process in the petrochemical industry due to overlapping boiling points and azeotrope formation. In this paper, liquid extraction of aromatic compounds (toluene and ethylbenzene) from aliphatic compounds (hexane and cyclohexene) using ionic liquids (1-butyl-3-methylimidazolium methylsulfate, BMimMSO₄, 1-propyl-3-methylimidazolium bis{trifluoromethylsulfonyl}imide, PMimNTf₂, and 1-butyl-3-methylimidazolium bis{trifluoromethylsulfonyl}imide, BMimNTf₂) as solvent was studied. (Liquid + liquid) equilibrium (ELL) data for the ternary systems {hexane (1) + ethylbenzene (2) + BMimMSO₄, or BMimNTf₂, or PMimNTf₂ (3)}, {hexane (1) + toluene (2) + BMimMSO₄ (3)} and {cyclohexene (1) + ethylbenzene (2) + BMimMSO₄ (3)} were experimentally determined at T = 298.15 K and atmospheric pressure. Moreover, an analysis of the influence of the structure of each compound on the phase behavior was also carried out. The ability of the studied ILs to separate aromatic from aliphatic compounds was evaluated in terms of the solute distribution ratio, β, and the selectivity, S. The Non Random Two-Liquid (NRTL) and UNIversal QUAsiChemical (UNIQUAC) thermodynamic models were used to correlate the experimental LLE data. Furthermore, the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) was applied to predict the (liquid + liquid) equilibrium. The suitability of this model to describe the phase behavior of the studied mixtures was evaluated comparing the experimental and calculated data.     

Phase separation of symmetric polymer mixtures in a common good solvent in the semidilute concentration regime

Monte Carlo simulations of lattice models of binary (AB) symmetric polymer mixtures (chain lengthsN _A=N _B=N) in a common good solvent are carried out and the phase diagrams and critical properties of the unmixing transitions are estimated and interpreted in terms of recent theories. Polymers are modeled by self-avoiding walks of lengthN=16, 32 and 64 on the simple cubic lattice. Data for vacancy concentrations of _V=0.6, 0.8 and 0.85 are analyzed. It is shown that forN=16, _V=0.85 no phase separation occurs, down to the lowest temperature, while forN=32, _V=0.85 still phase separation occurs but no longer is complete. Our results are compatible with a scaling theory based on a renormalization of the Flory-Huggins -parameter due to blob effects.Dedicated to Prof. Fischer on the occasion of his 65th birthday.Both of the authors are deeply indebted to Prof. E. W. Fischer, not only for help, support, and enlightening discussions, but even for bringing them together and suggesting to them to collaborate! By this catalytic action he actually played a decisive role in creating a longstanding and successful collaboration, the latest results of which are presented below.     

Simulation of adsorption of liquid mixtures of N2 and O2 in a model faujasite cavity at 77.5 K

Grand canonical Monte Carlo simulations of adsorption of N₂ and O₂ and their mixtures in a model zeolitic cavity 14 Å in diameter were performed at 77.5 K for pressures ranging from zero up to saturation, where the adsorbed phase is in equilibrium with coexisting vapor and liquid phases. The same intermolecular potential functions were employed for gas-gas interactions in the vapor, liquid, and adsorbed phases. The gas-solid interaction potential includes dispersion-repulsion energy, induced electrostatic energy, and an ion-quadrupole term to model the interaction of the electric field in zeolites like NaX with polar molecules like N₂. The simulation of the coexisting vapor and liquid phases reproduces the saturation properties of pure liquid oxygen and nitrogen at 77.5 K. Activity coefficients in the adsorbed phase derived from simulations as a function of cavity filling and composition show negative deviations from Raoult's law, even though the non-idealities in the bulk liquid phase have the opposite sign. The simulation of the surface excess isotherm for adsorption from liquid mixtures exhibits preferential adsorption of N₂ and has the commonly-observed quadratic shape skewed toward the more strongly adsorbed component. Micropore condensation is observed for oxygen but not for nitrogen. The condensation of oxygen is similar to a first order phase transition but because of the small number of molecules that can fit into a micropore, coexistence of the two phases is replaced by oscillations between gas- and liquid-like densities.     

Prediction of maxima and minima in the curve of total sorption parameter in ternary polymer systems. Influence of ternary interaction parameter

Flory-Huggins theory modified by Pouchly has been applied to predict maxima and minima in the curve of total sorption in ternary polymer systems formed by a polymer and two liquids. In this work, different diagrams based on experimental magnitudes easily obtained such as the difference in affinities of liquids, solvents and non solvents, and the solvent molar volume ratio. Total sorption parameter has been considered to be the decisive magnitude to define extrema conditions in both cosolvent and cononsolvent ternary polymer systems. The theoretical prediction is not altered by the inclusion of ternary interactions. Different examples of ternary systems dealing with vinyl polymers and polydimethyl siloxane have been used to test the above formalism.     

Free volume properties of model fluids and polymers: Shape and connectivity

The Cavity Energetic Sizing Algorithm (CESA) method of in 't Veld (J Phys Chem B 2000, 104, 12028) is extended to characterize the nonspherical nature of free volume. The new technique is introduced with reference to simple model fluids (water, hard spheres, and a Lennard‐Jones fluid) and then applied to polymers of interest to membrane scientists. A set of shape parameters is introduced, characterizing nanopores in terms of surface area, volume, radius of gyration, and span. Results are presented for Lennard‐Jones fluid and hard sphere fluid, and for the high free volume polymers (poly‐trimethyl‐silyl‐propane) poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) and a random copolymer of 2,2‐bis(trifluoromethyl)‐4,5‐difluoro‐1,3‐dioxole (TFE/BDD). PTMSP is observed to have an average free volume cluster span of 1.43 nm, compared to TFE/BDD with an average cluster span of 0.98 nm, consistent with the markedly higher permeability of CO₂ observed in PTMSP. An additional method for measuring free volume is introduced, similar to a method introduced by Greenfield and Theodorou (Macromolecules 1993, 26, 5461; Mol Simul 1997, 19, 329; Macromolecules 1998, 31, 7068; 2001, 34, 8541), which measures free volume relative to a specific probe. The method captures 1–3 times the fractional cavity volume captured by CESA. Free volume measurements are presented for a set of polysulfones with respect to noble gas probes (J Chem Phys 2005, 122, 84906; J Mol Struct 2005, 739, 173). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:1385–1393, 2006     

Phase behavior in mixtures of cationic and anionic surfactants in aqueous solutions

Phase behavior of cationic/anionic surfactant mixtures of the same chain length (n=10, 12 or 14) strongly depends on the molar ratio and actual concentration of the surfactants. Precipitation of catanionic surfactant and mixed micelles formation are observed over the concentration range investigated. Coacervate and liquid crystals are found to coexist in the transition region from crystalline catanionic surfactant to mixed micelles.The addition of oppositely charged surfactant diminishes the surface charge density at the mixed micelle/solution interface and enhances the apparent degree of counterion dissociation from mixed micelles. Cationic surfactants have a greater tendency to be incorporated in mixed micelles than anionic ones.     

表面扩散对CO氧化反应一级相变点的影响：蒙特卡罗模拟

CO氧化反应无论在化学工业还是在环境保护化学中都占有重要一席，特别是它常被用作研究多相催化反应基本过程的模型反应．研究表明，这一反应体系具有复杂的动力学行为，其中包括表面吸附物种的动力学相变、速率振荡和催化剂表面的结构重排等四人们还发现，当CO和O。按化学计量     

Sampling potential energy surface of glycyl glycine peptide: Comparison of Metropolis Monte Carlo and stochastic dynamics

A comparative study was carried out to test the efficiency with which Metropolis Monte Carlo (MC) and stochastic dynamics (SD) sample the potential energy surface of the N-acetyl glycyl glycine methylamide peptide as defined by the united atom AMBER* force field. Boltzmann-weighted ensembles were generated with variations of all internal degrees of freedom (i.e., stretch, bend, and torsion) for a single N-acetyl glycyl glycine methylamide molecule at 300 K by 10⁸-step MC and 100-ns SD simulations. As expected, both methods gave the same final energetic results. However, convergence was found to be ∼10 times faster with MC than with SD as measured by comparisons of the populations of all symmetrically equivalent conformers. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1294–1299, 1998     

Phase behavior of amphiphiles at liquid crystals/water interface: A coarse-grained molecular dynamics study

We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal （LC）/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails.     

Structural properties of liquid formamide—N,N-dimethylformamide mixtures

Monte Carlo simulations of formamide—N,N-dimethylforamide mixtures in the whole range of compositions were carried out at 298 K. Structural properties were investigated by calculating the atom-atom spatial distribution functions, generalized spatial distribution functions, concentrations of closed cycles of H-bonds, and other properties of the system of hydrogen bonds. It was found that local spatial regions with the structure of pure components are conserved in a wide range of concentrations. The regularities of manifestation of solvophobic effects have been established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2421–2429, December, 1998.     

Phase behavior, interfacial composition and thermodynamic properties of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and n-decane as oils

Phase diagrams of pseudo-quaternary systems of cetyltrimethylammonium bromide (CTAB)/polyoxyethylene(20)cetyl ether (Brij-58)/water/1-butanol (or 1-pentanol)/n-heptane (or n-decane) at fixed omega (=[water]/[surfactant]) of 55.6 were constructed at different temperatures (293, 303, 313, and 323 K) and different mole fraction compositions of Brij-58 (X(Brij-58)=0, 0.5, and 1.0 in CTAB + Brij-58 mixture). Pure CTAB stabilized systems produced larger single-phase domains than pure Brij-58 stabilized systems. Increasing temperature increased the single-phase domain in the Brij-58 stabilized systems, whereas the domain decreased in the CTAB stabilized systems. For mixed surfactant systems (with X(Brij)=0.5) negligible influence of temperature in the studied range of 293 to 323 K on the phase behavior was observed. Interfacial compositions of the mixed microemulsion systems at different temperature and different compositions were evaluated by the dilution method. The n(a)(i) (number of moles of alcohol at the interface) and n(a)(o) (number of moles of alcohol in the oil phase) determined from dilution experiments were found to decrease and increase respectively for CTAB stabilized systems, whereas an opposite trend was witnessed for Brij-58 stabilized systems. The energetics of transfer of cosurfactants from oil to the interface were found to be exothermic and endothermic for CTAB and Brij-58 stabilized systems, respectively. At equimolar composition of CTAB and Brij-58, the phase diagrams were temperature insensitive, so that the enthalpy of the aforesaid transfer process was zero.     

Phase behavior of tetramethylpolycarbonate blends with styrene‐based methacrylate copolymers and their interaction energies

The miscibility of tetramethylpolycarbonate (TMPC) blends with styrenic copolymers containing various methacrylates was examined, and the interaction energies between TMPC and methacrylate were evaluated from the phase‐separation temperatures of TMPC/copolymer blends with lattice‐fluid theory combined with a binary interaction model. TMPC formed miscible blends with styrenic copolymers containing less than a certain amount of methacrylate, and these miscible blends always exhibited lower critical solution temperature (LCST)‐type phase behavior. The phase‐separation temperatures of TMPC blends with copolymers such as poly(styrene‐co‐methyl methacrylate), poly(styrene‐co‐ethyl methacrylate), poly(styrene‐co‐n‐propyl methacrylate), and poly(styrene‐co‐phenyl methacrylate) increase with methacrylate content, go through a maximum, and decrease, whereas those of TMPC blends with poly(styrene‐co‐n‐butyl methacrylate) and poly(styrene‐co‐cyclohexyl methacrylate) always decrease. The calculated interaction energy for a copolymer–TMPC pair is negative and increases with the methacrylate content in the copolymer. This would seem to contradict the prediction of the binary interaction model, that systems with more favorable energetic interactions have higher LCSTs. A detailed inspection of lattice‐fluid theory was performed to explain such phase behavior. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1288–1297, 2002     

Influence of transesterification reactions on the miscibility and thermal properties of poly(butylene/diethylene succinate) copolymers

Poly(butylene/diethylene succinate) block copolymers (PBSPDGS), prepared by reactive blending of the parent homopolymers (PBS and PDGS) in the presence of Ti(OBu)₄, were analyzed by ¹H-NMR, TGA and DSC, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. ¹H-NMR analysis evidenced the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis of the melt-quenched samples showed that the melting peak, due to the crystalline phase of PBS, tends to disappear with increasing mixing time and therefore with decreasing the block length in the copolymers. As concern miscibility, a single homogeneous amorphous phase always occurred, independently on block length. Nevertheless, a phase separation, due to the tendency of the PBS blocks to crystallize, was evidenced in the copolymers with long butylene succinate sequences. The results obtained indicated that the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the block copolymers.     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

Conformational Aspects and Intramolecular Phase Separation of Alternating Copolymacromonomers: A Computer Simulation Study

Summary: Using the bond fluctuation model (BFM), simulations have been performed on molecular bottle brushes with two chemically different types of side chains. In the first part of this work, rigidity of the backbone is imposed. The influence of solvent quality and side chain length on the intramolecular phase separation of side chain material, leading to Janus cylinders, has been investigated and compared to theoretical predictions. In the second part of this work, the restriction of rigidity for the backbone is relaxed. In a poor solvent, the side chain material collapses into a globular state. Several globules containing each one type of side chain material are connected together by backbone material. When imposing different solvent conditions for both types of side chains, a bending of the backbone is found as predicted by theory and observed in very recent experiments.

Comparison between typical snapshots in θ solvent. The side chain length is 25 beads. Dark and light coloured side chains repel each other.