[PDF] Diffusion In Polymer Solvent Systems eBook

Author : Roy Allen Waggoner
Publisher :
Page : 312 pages
File Size : 49,73 MB
Release : 1993
Category : Nuclear magnetic resonance
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"Pulsed gradient NMR techniques have been used to study self-diffusion in polymer solutions. The systems studied include toluene, cyclohexane, ethylbenzene, chloroform, t-butyl acetate, and methyl ethyl ketone in polystyrene; methyl methacrylate in poly(methyl methacrylate); poly(ethylene oxide) in water; and water in biological tissue. The polymer diffusion data are evaluated in terms of scaling theory as they relate to the scaling of the polymer diffusion coefficient with molecular weight. The solvent diffusion data are evaluated with kinetic and free-volume theories. In addition a relatively simple dependence of diffusion coefficient on polymer volume fraction is derived from free-volume theory. The solvent diffusion data are employed in a model which simulated the drying of a coating by solvent evaporation. Solvent volatility is determined from solvent activity at the surface. Diffusion within the film is handled by the solution of Fick's second Law by the Crank-Nickolson implicit method. Without using any adjustable parameters the model can do an excellent job of predicting the drying curves for a good solvent-polymer two component system. The model is less successful with poorer solvents"--Abstract, leaf iii.

Author : Hülya Eser
Publisher :
Page : 180 pages
File Size : 36,2 MB
Release : 2004
Category : Inverse gas chromatography
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In this study, thermodynamic properties, namely retention volume, infinitely dilute weight fraction activity coefficient, Flory- Huggins interaction parameter, solubility parameters of solute and polymer, partition coefficient and diffusion coefficients of the various solvents in poly (methyl methacrylate co butyl methacrylate) (PMMA co BMA) and poly (lactide co glycolide) (PLGA) at infinite dilution of the solvent have been determined by inverse gas chromatography (IGC). In this technique, a small amount of the solvent was injected into the capillary column and its retention time was measured and used to calculate several polymer-solvent interaction parameters which are mentioned above. The solutes used in this study were methanol, ethanol, propanol, butanol, methyl acetate, ethyl acetate, propyl acetate, dichloromethane, trichloromethane, acetone, methyl methacrylate, butyl methacrylate, water for PMMA co BMA and acetone, dichloromethane, trichloromethane, ethyl acetate, ethyl alcohol, tetrahydrofuran, water for PLGA. The glass transition temperature of the polymers were determined as 106 0C and 42 0C for PMMA co BMA and PLGA respectively by differential scanning calorimetry. Experiments were performed in the range of 150-200 0C for PMMA co BMA and 80-120 0C for PLGA which are above the glass transition temperature of the polymer. The thermodynamic results, obtained from the experiments, indicated that trichloromethane and dichloromethane were the most suitable solutes among all the solvents studied for both of the polymers. The partition (K) and diffusion coefficients (Dp) of various solvents at infinite dilution of the solvent were calculated by using the model developed by Pawlisch et al. (1987). The optimum K and Dp values that best fit the data were found and the model predicted experimental data very well. In summary, IGC method is a powerful tool for the determination of thermodynamic and diffusion properties of solvent in polymer at infinite dilution of the solvent. Vrentas- Duda free volume theory was used to correlate the diffusion data and to investigate the effect of solvent size on diffusion process. The theory has shown to correlate diffusion data above the glass transition temperature very well for the PMMA-co-BMA .solvent system.

Author :
Publisher :
Page : 36 pages
File Size : 30,16 MB
Release : 1994
Category :
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Self-diffusion coefficients of several different solvents in polystyrene, as well as, methyl methacrylate in poly(methyl methacrylate) have been determined at polymer concentrations from 0 to 50 wt% at 25 deg C. The solvents used for the polystyrene solutions were toluene, ethylbenzene, cumene, t-butyl acetate, chloroform, and methyl ethyl ketone. The diffusion data was used to evaluate several theories for the concentration dependence of the solvent diffusion coefficients, and in most cases the reduced diffusion coefficients, of solvents in polymer-solvent systems. In addition to the experimental data presented here, literature data for several systems were also used to test the models. The theories evaluated were based on widely different concepts including electrical conductivity, tortuosity, kinetic theory, and free-volume. The results indicate that the kinetic theory and free-volume approaches fit the data most consistently, with the kinetic theory approach preferred at lower polymer concentrations and the free-volume approach favored at higher polymer concentrations. Self diffusion, Kinetic theory, Free volume, Solvents, Polymers.