Polystyrene tracer diffusion coefficient

Figure 4.24. Diffusion coefficients as functions of the composition in the miscible blend polystyrene-poly(xylenyl ether) (PS-PXE) at a temperature 66 °C above the (concentration-dependent) glass transition temperature of the blend, measured by forward recoil spectrometry. Squares represent tracer diffusion coefficients of PXE (VpxE = 292), circles the tracer diffusion coefficients of PS and diamonds the mutual diffusion coefficient. The upper solid line is the prediction of equation (4.4.11) using the smoothed curves through the experimental points for the tracer diffusion coefficients and an experimentally measured value of the Flory-Huggins interaction parameter. The dashed line is the prediction of equation (4.4.11), neglecting the effect of non-ideality of mixing, illustrating the substantial thermodynamic enhancement of the mutual diffusion coefficient in this miscible system. After Composto et al. (1988).

Although cannot be measured in DLS, a closely related tracer diffusion coefficient Dj can be measured. In the tracer diffusion, the motion of a labeled solute called a probe or a tracer is traced selectively. A second solute called a matrix is added to the solution and its concentration is varied, whereas the concentration of the probe molecules is held low. The matrix must be invisible, and the probe must be visible. We can give a large contrast between the matrix and probe by choosing a pair of solvent and matrix that are nearly isorefractive, i.e., having the same refractive index. Then, the light scattering will look at the probe molecules only. For instance, we can follow the tracer diffusion of polystyrene in a matrix solution of poly(dimethyl siloxane) in tetrahydrofuran. 

Figure 4.41. Tracer diffusion coefficient Di of polystyrene in solutions of matrix polymer, poly(vinyl methyl ether), in o-fluorotoluene at various concentrations of the matrix polymer, plotted as a function of molecular weight Mps of polystyrene. The solvent is isorefractive with the matrix polymer. The concentration of the matrix polymer and the slope obtained in the best fitting by a power law (straight line) are indicated adjacent to each plot. (From Ref. 53.)...

Figure 12.16 Ratio of polystyrene tracer diffusion coeflScient (D,) in toluene swollen PMMA gel to diffusion coefficient of polystyrene in dilute toluene solution ( ) (/i ) values for PS tracer in PMMA solutions. Reproduced with pennission from the American Chemical Society from Ref. [S3]...

We have used forward recoil spectrometry to measure the mutual diffusion and tracer diffusion coefficients, D and D, in the miscible polymer blend of deuterated polystyrene (d-PS) poly(xylenyl ether) (PXE). Using the fast theory of mutual diffusion, D is related to the D, degree of polymerization N, and volume fraction of the individual blend components by,... 

B. Hanley, M. Tirrel, and T. P. Lodge. The behavior of the tracer diffusion coefficient of polystyrene in isorefractive solvents composed of polyvinyl methyl ether and o-fluorotoluene. Polym. Bull. Berlin, 14 (1985), 137-142. 

N. Nemoto, T. Kojima, T. Inoue, et al. Self-diffusion and tracer-diffusion coefficient and viscosity of concentrated solutions of linear polystyrenes in dibutyl phthalate. 

F ure 12.15 Diffusion coefficient of polystyrene tracer in polyvinyl methyl ether gels as a function of tracer molecular weight. Diffusion coefficients normalised by ratio of molecular weight between crosslinks of gels. Reprinted with permission from [52]. Copyright 1992 American Chemical Society... 

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