Characterization of thermal diffusion of polystyrene in binary mixtures of THF/dioxane and THF/cyclohexane (original) (raw)
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Thermal and mass diffusion in a semidilute good solvent-polymer solution
The Journal of Chemical Physics, 1999
The Soret coefficient S T and collective ͑mass͒ diffusion coefficient D c of polystyrene dissolved in the good-solvent toluene has been measured over a range of concentrations and molecular masses with an optical beam-deflection method. Our measurements indicate that S T scales inversely with the polymer translational diffusion coefficient in dilute solutions, exhibits a power-law scaling with polymer concentration, and an independence of polymer molecular mass in semidilute solutions. These findings are consistent with the known scaling of 1/D c in dilute and semidilute polymer solutions, the relative insensitivity of the thermal-diffusion coefficient D th of polystyrene in toluene to polymer concentration, and the relation S T ϭD th /D c from irreversible thermodynamics. We are able to represent our S T and D c data by theoretically motivated reduced-concentration master curves, but the concentration-molecular mass scaling variables are found to be different for each transport property, a result contrary to theoretical expectations. However, the asymptotic concentration scaling exponents deduced from these data fits are compatible with de Gennes' scaling arguments for D c and with modern estimates of the chain-size exponent for swollen polymers in good solvents.
Journal of Polymer Engineering, 2005
Attenuated Total Reflection (ATR) spectroscopy was used to study the interdiffusion mechanism at the interface of Polystyrene (PS) and Poly(vinyl methyl ether) (PVME), at temperatures above and below the glass transition temperature (T g) of PS, but in the miscible region. One molecular weight of PVME and 13 molecular weights of PS, both below and above the critical molecular weights of PS were used to investigate the effect of molecular weight on mutual diffusion process both below and above the critical molecular weight for entanglements of PS. To extract the diffusion coefficient from experimental data, we used the approach suggested by Jabbari and Pepas. Both Fickian and Case-II diffusion were necessary to fit the PVME concentration profile for the various molecular weights. The experimental results were also compared with the slow-mode and the fast mode theories2-3.
Self-diffusion coefficients of solvents in polystyrene gels
Journal of the American Chemical Society, 1987
6-d isotopomers; 2-methyl-endo-2-bicyclo[2.2.l]heptanol and its methyl-d3 and 3,3-d2 isotopomers; 2-cyclopropyl-2-propanol and the 1,1,1,3,3,3-d,5 isotopomer; and 2-methyl-2-adamantanol and the methyl-d3 isotopomer. Alcohols were purified by dry column flash chromatography using Merck silica gel 60 (finer than 230 mesh) or preparative gas chromatography on a 6-m column packed with 5% Carbowax on 80/100 mesh Chromosorb W High Pack. Chlorides were prepared by the procedure of Brown et al.34 or the procedure of Norris and O l m~t e a d )~ and were used without further purification.
Thermal and collective diffusion in polymer solutions: A small angle light scattering study
Optics Communications, 1985
Two experimental arrangements are described whereby the thermal and collective diffusion coefficients X and D~ of semi-dilute or concentrated polymer solutions may be measured using small angle light scattering. The first is achieved by measuring the characteristic time ~" of the decay in the angular spread of the nonlinear diffraction pattern following an abrupt reduction of the incident laser power, together with a knowledge of the beam diameter. The second is obtained by allowing the solution to develop a slight refractive index gradient through surface evaporation of the solvent, and then following the decay in intensity of the light scattered through a small angle after the solution has been shaken.
Macromolecules, 1998
A new method combining thermal field-flow fractionation (ThFFF) and SEC-MALLS is proposed for the measurement of the thermal diffusion coefficient DT for polydisperse polymeric samples. This method should greatly increase the range of applicability of ThFFF for characterization of block copolymers and also for studies of thermal diffusion, an interesting phenomenon not yet well understood. ThFFF is one of only a few techniques (e.g., thermal diffusion forced Rayleigh scattering) that can determine DT values of polymers. The values of DT can be used to reflect the surface composition of block copolymer molecules as reported in recent studies. Currently, the value has been measured with ThFFF based on the sample peak maximum method, which can introduce errors when the sample has a broad MW distribution. The method proposed here measures DT by taking all digitized points in the entire sample peak into consideration, and has been tested with polystyrene, poly(tert-butylstyrene), and some copolymer microgels. Preliminary results are presented and discussed.
Journal of Polymer Science Part B: Polymer Physics, 1999
A comparison between various methods to determine diffusion coefficients of polymers in dilute solutions has been made. It is shown that Taylor dispersion analysis (TDA), dynamic light scattering (DLS), hydrodynamic chromatography (HDC), and size exclusion chromatography (SEC) can all be used to accurately determine diffusion coefficients when the polymer samples have low polydispersities. By the analysis of a series of practically representative styrene acrylonitrile copolymer (SAN) samples, it is shown that polydispersity of the samples and the presence of lowmolecular-mass material cause considerable differences between the methods. It was found that TDA is mostly disturbed by the presence of low-molecular-mass material, whereas DLS is more sensitive to the polydispersity of the polymer. With broad samples, DLS gives the Z-average diffusion coefficient. SEC can be used to obtain a diffusion coefficient distribution as well as an average diffusion coefficient of a polydisperse sample. Although, the same was expected for HDC, it was found that this method could only be successfully used for polymer samples having low polydispersities. Deviations between SEC, HDC, and TDA found for narrow samples were not related to the chemical composition of the samples.
Polymer, 1987
The technique of dynamic light scattering from isorefractive ternary solutions has been used to study the translational diffusion behaviour of 12-arm star polystyrenes (PS) in dilute and concentrated solutions of poly(vinyl methyl ether) (PVME). PS molecular weights ranged from 5.5 x 104 to 1.69 x 106. The PVME molecular weight was 1.4 x 105, and the PVME concentration was varied from 0.001 to 0.30g ml-l. The concentration dependence of diffusion is well described by the functional form DID o = exp(-ac"), although there is some evidence that the star dimensions decrease with increasing PVME concentration. Comparison with the diffusion behaviour of linear PS in PVME solutions suggests that, for these molecular weights of PS and PVME, the diffusant topology is not important, and thus reptation is not a significant mechanism under these conditions. At the same time, neither the Stokes-Einstein relation nor a simple scaling function, f(R/~), can describe the observed behaviour. These results are interpreted as reflecting substantial PVME mobility, relative to the PS stars.
Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene
Polymer, 2012
Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C n , with n ¼ 2, 6e16) in amorphous polystyrene at temperatures from 35 C to 165 C, that is, both below and above the polymer glass transition temperature of 100 C. All the mass uptake results are well described by a simple Fickian model (for t < t 1/2 ) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n 2 D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.