Polymer conformation in mixed aqueous-polar organic solvents

The conformation of the common polysaccharide dextran has been investigated in mixed solvents at two different temperatures using viscosity measurements. In particular we considered binary mixtures of water with the polar organic solvents glycerol, formamide, dimethylsulfoxide, or ethanol. The intrinsic viscosity of dextran T500 in the different systems has been determined, and the solvent effects, as manifested in variations of the dextran intrinsic viscosity and coil radius, have been correlated to the surface tension and the fractional solubility parameters of the solvent mixture. The coil dimension changes observed in the different solvent mixtures are consistent with expectations from water-cosolvent-dextran interactions, especially as they pertain to hydrogen bonding.     

Calculation of solubility of solid solutes in mixed non-aqueous solvents within the limits of the theory of molecular association

A method for calculating the solubility of solid substances in mixed non aqueous solvents is proposed based on the theory of molecular association and a simple lattice model (ASL = Associated Solution + Lattice). This method provides the calculation of the solubility of solids in mixed non aqueous solvents using only the molecular association parameters and the value of the interchange energy ω_AB that is derived from the phase equilibrium data in a mixed solvent.     

On the theory of solute solubility in mixed solvents

A series of equations are developed for the study of the effects of cosolvents on the solubility of a solute in mixed solutions where the solute displays a finite solubility. The equations differ depending on the scale used for the solute (and cosolvent) concentrations. The expressions use Kirkwood-Buff integrals to relate the changes in solubility to changes in the local solution composition around the solute and can be applied to study any type of ternary system including electrolyte cosolvents. The expressions provided here differ from previous approaches because of the use of a semi-open ensemble and the extension to finite solute solubilities.     

High-precision gravimetric technique for determining the solubility and diffusivity of gases in polymers

An in situ gravimetric technique, employing an electrobalance, is described for determining the solubility and diffusivity of gases in polymers over extended ranges of temperature and pressure. Solubilities of CO₂ in polystyrene at 35°C were measured as a test case; the results are in excellent agreement with the literature values determined by the pressure decay method. Solubility and diffusivity results are also reported for PVC-CO₂ at 35°C and for PS-1,1,1,2-tetrafluoroethane at 30, 90, and 120°C. A comparison with other studies shows the in situ method to be more efficient and precise than the ones based on weighing the gas-saturated polymer under ambient conditions. The kinetics of gas sorption were analyzed in terms of two data reduction techniques to derive diffusion coefficients. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2025–2032, 1998     

The solubility and solvation of salts in mixed nonaqueous solvents. 1. Potassium halides in mixed aprotic solvents

The solubilities of potassium fluoride, chloride, and bromide in acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide and in binary mixtures of these solvents were determined at 25°C. The standard molar Gibbs free energies of solution, _solnG°, in the neat solvents were related to the polarizabilities and basicities of the anions and the dipole moments and acidities of the solvents. The values of _solnG° in the mixtures were fitted by expressions from the quasi-lattice quasi-chemical theory. The mean number of each kind of solvent in the nearest environment of the ions was obtained from these results.     

Diffusion constants of polymers in mixed solvents

Dynamics of polymers in mixed solvents are investigated on the basis of linear response theory and mean field arguments. Particular attention is given to the coupling between polymer and fluid fluctuations. This coupling is enhanced by polymer–solvent interaction asymmetry and mixed solvent incompatibility. Cooperative and fluid diffusion constants are analyzed in terms of the interactions in the medium and some predictions for light scattering experiments are made. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3976–3980, 2004     

A unified cosolvency model for calculating solute solubility in mixed solvents

Organic solvents are amongst the most powerful solubilization agents for a large number of water-insoluble drugs. A number of equations has been reported for mathematical representation of solute solubility in mixed solvents. The question is then posed--is there a mathematical difference between these models? To address this point, it has been demonstrated that all cosolvency models could be made equivalent by using algebraic manipulations. In order to familiarize the readers with the available cosolvency models, they are briefly reviewed. The models can be divided into two mathematical categories, i.e. linear and non-linear models. The linear models include: the log-linear, extended Hildebrand solubility approach, excess free energy equations, combined nearly ideal binary solvent/Redlich-Kister equation and Margule equations which can be converted to a general single model which expresses the logarithm of mole fraction solubility of a solute as a power series of volume fraction of the cosolvent. The non-linear models include the mixture response surface methods, two step solvation model and modified Wilson model which can be converted to a non-linear general form. Also, it has been shown that both the general single model and a non-linear general model are mathematically identical. To show the applicability of the models on real experimental data, 35 data sets have been collected from the literature. Both linear and nonlinear models produced comparable accuracies when an equal number of constant terms was employed in numerical analyses.     

Specific interactions in mixed electrolyte solutions from solubility measurements

The solubility of thallium I chloride in a wide range of dilute electrolyte solutions is interpreted using a new specific-interaction equation for activity coefficients. This equation is shown to be consistent with the solubility data, but the Guggenheim specific-interaction equation is not. The relation of interaction coefficients to ion association is discussed.     

Molecular model for solubility of gases in flexible polymers

We propose a model for a priori prediction of the solubility of gases in flexible polymers. The model is based on the concept of ideal solubility of gases in liquids. According to this concept, the mole fraction of gases in liquids is given by Raoult's law with the total pressure and the vapor pressure of the gas, where the latter may have to be extrapolated. However, instead of considering each polymer molecule as a rigid structure, we estimate the effective number of degrees of freedom from an equivalent freely jointed bead‐rod model for the flexible polymer. In this model, we associate the length of the rods with the molecular weight corresponding to a Kuhn step. The model provides a tool for crude estimation of the gas solubility on the basis of only the monomer unit of the polymer and properties of the gas. A comparison with the solubility data for several gases in poly(dimethylsiloxane) reveals agreement between the data and the model predictions within a factor of 7 and that better model results are achieved for temperatures below the critical temperature of the gas. The model predicts a decreasing solubility with increasing temperature (because of the increasing vapor pressure) and that smaller gas molecules exhibit a lower solubility than larger ones (e.g., CH₄ has a smaller solubility than CO₂), which agrees with the experimental data. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 701–706, 2003     

A flavin analogue with improved solubility in organic solvents

We report the synthesis and initial electrochemical characterization of a benzene-soluble flavin analogue: N(10)-2,2-dibenzylethyl-7,8-dimethylisoalloxazine (DBF, 1). This analogue, which has an unmodified flavin headgroup, is intended for use in the spectroscopic examination of the electronic effects of flavin hydrogen bonding in simple model systems in aprotic, non-hydrogen bonding solvents. With future spectroscopic studies in mind, we have developed a synthetic route, which allows the incorporation of isotopic labels using inexpensive starting materials.     

Multiple solubility maxima of oxolinic acid in mixed solvents and a new extension of Hildebrand solubility approach

A new extension of the Hildebrand solubility approach which describes drug solubility in solvent mixtures showing multiple solubility peaks, the chameleonic effect, is proposed. The experimental solubilities of oxolinic acid were measured at 25 degrees C in solvent mixtures of ethanol-water and ethanol-ethyl acetate. A plot of the mole fraction of the drug against the solubility parameter (delta) of the solvent mixtures displays two peaks at delta = 30.78 MPa1/2 (80% v/v of ethanol in water) and at delta = 20.90 MPa1/2 (30% v/v of ethanol in ethyl acetate). The new extension proposed reproduces two solubility peaks. The thermograms of the solid phase before and after equilibration with the solvent mixtures did not show significant changes. The new extension was also tested with experimental data previously reported for drugs showing two solubility peaks of different height. The accuracy of other published models for describing two solubility maxima is also compared.     

Equilibrium solubility of 6-propyl-2-thiouracil in nine pure solvents: Determination,correlation, Hansen solubility parameter and thermodynamic properties

Investigation upon the solid–liquid equilibrium on solubility data of 6-propyl-2-thiouracil (PLT) in pure organic solvents is essential for separation and purifying in industry process. In this work, PLT solubility in nine neat solvents was experimentally determined at 278.15 K–323.15 K under P = 0.1 MPa. These selected solvents were tetrahydrofuran(THF), acetone, acetonitrile,1-butanol,1-pentanol, 2-butanol, methyl acetate, ethyl acetate,1-propyl acetate, respectively. Experiment results showed that solubility was consistent with temperature and decreased according to the order: THF > acetone>1-butanol≈1-pentanol> 2-butanol > methyl acetate > ethyl acetate>1-propyl acetate > acetonitrile. Solvent effect and Hansen solubility parameter (HSP) were incited to explain dissolution rule on solute. Four thermodynamic models (modi?ed Apelblat model, Van't model, λh model and NRTL model) were adopted to correlate PLT solubility and provide good correlations on basis of RD, ARD and RMSD. In addition, thermodynamic properties (ΔH°, ΔS° and ΔG°) of PLT dissolution process in pure solvents were discussed and proved to be endothermic, entropically driven and non-spontaneous process.     

Measured and calculated solubility of polymers in mixed solvents: Monotony and cosolvency

By a study of two ternary systems, 4-heptanon–1-chlorobutane–poly(methyl methacrylate) and 2-butanol–1-chlorobutane–poly(methyl methacrylate), differing only in one component of the mixed solvent, two types of demixing behavior are demonstrated: i.e., a monotone change with composition of the mixed solvent (monotony), of which the first system is a good example, and the synergistic behavior (cosolvency) exhibited by the second system. The situation can be seen most clearly from the binodal edges (precipitation thresholds as a function of solvent composition) which were constructed from various types of sections through the binodal surface of the systems. In order to compare experimental results with theoretical calculations, we first characterized the binary subsystems. The polymer solutions, representing conventional (endothermal) theta systems, were investigated by light scattering and cloud point measurements. For the cosolvent 2-butanol–1-chlorobutane the necessary thermodynamic information was accessible from vapor pressure measurements. Applying the Prigogine–Patterson theory to the polymer solutions and using the single-liquid approximation of Scott for the ternary systems yielded theoretical binodal edges in good agreement with experiment except for the branch belonging to mixed solvents rich in 2-butanol. This finding is explained by an abnormal amplification of preferential solvation effects due to the existence of an association equilibrium of the alcohol via hydrogen bonds.     

Extraction of aroma compounds in blackcurrant buds by alternative solvents: Theoretical and experimental solubility study

This study was designed to evaluate the performance of nine alternative solvents (α-pinene, MeTHF, ethyl acetate, methyl acetate, ethyl lactate, butanol, isopropanol, ethanol and CO₂ supercritical fluid) for extracting aromas from blackcurrant buds (Ribes nigrum L) compared to that of n-hexane, commonly used. This study has been performed via experimentation and simulation using Hansen solubility methodology for the comprehension of the dissolving mechanism. Experimentally, the extracts were analysed to compare the solvents performance in terms of aroma compositions. The results indicated that an alternative solvent, i.e. MeTHF, could be the most promising one for n-hexane substitution with good yield and selectivity of aromas.     

Density and viscosity of magnesium sulphate in formamide + ethylene glycol mixed solvents

Densities (ρ) and viscosities (η) of different strengths of magnesium sulphate (MgSO₄) in varying proportions of formamide (FA) + ethylene glycol as mixed solvents were measured at room temperature. The experimental values of ρ and η were used to calculate the values of the apparent molar volume, (φ_1,), partial molar volume, (φ₁,^ℴ) at infinite dilution,A- andB-coefficients of the Jones-Dole equation and free energies of activation of viscous flow, (Δμ ₁ ^0* ) and (Δμ ₂ ^0* ), per mole of solvent and solute respectively. The behaviour of these parameters suggests strong ion-solvent interactions in these systems and also that MgSO₄ acts as structure-maker in FA + ethylene glycol mixed solvents.     

DPD Simulations of PMMA-Oleic Acid Mixture Behaviour in Organic Capped Nanoparticle Based Polymer Nanocomposite

Dissipative Particle Dynamics has been used to investigate the different morphology of polymer nanocomposites. Such a study was addressed to the definition of a suitable tool for understanding the distribution of oleic acid (OA) capped nanoparticles embedded into poly-methylmethacrylate (PMMA) matrix for the formation of nanocomposite materials. In particular, simulations of PMMA/OA mixtures at different composition have exhibited the self-assembly of amphiphiles to form separated nanosized domains with different morphologies going from spheres, to tubules up to the formation of continuous planar sheets as the OA composition increases. On the other hand, simulations carried out on nanocomposite systems have shown that NPs do not perturb the observed phase behaviour of PMMA/OA mixtures. In fact, at low OA compositions nanoparticles are confined in the spherical lipid domains to form NP clusters, while at high OA composition NPs appear homogeneously distributed in the continuous lipid domain.     

Supramolecular Design Strategy of a Water-Soluble Diphenylguanidine-Cyclodextrin Polymer Inclusion Complex

Diphenylguanidine (DPG) is a widely used secondary accelerator for the vulcanization of natural rubber (NR) latex. However, its low water solubility and high toxicity limit its use in high-end NR products. In this study, a water-soluble inclusion complex of DPG and a β-cyclodextrin polymer (β-CDP), termed DPG-β-CDP, was prepared through supramolecular interactions and characterized using Fourier-transform infrared spectroscopy, ¹H NMR, scanning electron microscopy, and UV-vis spectroscopy techniques. In comparison with that of DPG, the water solubility of DPG-β-CDP was greatly enhanced because of the water-soluble host molecule. The molar ratio of DPG to the CD unit in β-CDP was determined to be 1:1. At 25 °C, the binding constant of DPG-β-CDP was found to be 9.2 × 10⁵ L/mol by UV-vis spectroscopy. The proposed method for forming inclusion complexes with high potential for use as water-soluble vulcanization accelerators is promising.     

Rapid microfluidic screening of CO(2) solubility and diffusion in pure and mixed solvents

We present a high-throughput method to determine rapidly and simultaneously the solubility and the diffusivity of CO(2) in pure solvents and mixtures using segmented flow in a microchannel. Gas bubbles are injected via a T-junction into the liquid stream and the evolution of the bubbles' lengths are followed visually. We measure both solubility and diffusion coefficient from the shrinkage and expansion of the bubbles. The presented method is used to study the physical absorption of CO(2) in various pure solvents and to screen the complete composition space of binary and ternary mixtures.