Polystyrene solutions, diffusion

Diffusion coefficient from dynamic light scattering for dilute polystyrene solutions in the good solvent toluene (open circles). The lines show the limiting power laws with slopes expected by Eq. (8.23) (i/=ij2 inside the thermal blob and i/ = 0.588 at higher molar--------... 

Details concerning the experimental apparatus and the experimental procedure will be presented elsewhere [ 18] The polystyrene solutions used in the experiment were taken from the same batches as those used by Zhang et al. [22] for measuring the mass-diffusion coefficient and the Soret coefficient of these polymer solutions. 

Characteristic width of the photon beat spectrum Itk of polystyrene solutions as a function of the wave vector AT. The width is normalized by the diffusion width />o A, and the wave vector is expressed through KR when R is the coil radius. The squares and the triangles correspond to two very different molecular weights, suggesting that there is indeed a universal scaling form. From M. Delsanti, Ph.D. Thesis, Orsay, 1978. 

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]...

S. Pickup and F. D. Blum. Self-diffusion of toluene in polystyrene solutions. Macromolecules, 22 (1989), 3961-3968. 

It is easy to measure the potential of this system and it has been found that membranes of polystyrene, linseed oil and a tung oil varnish yielded diffusion potentials of 43-53 mV, the dilute solution being always positive to the concentrated. Similar results have been obtained with films of nitrocellulose, cellulose acetate , alkyd resin and polyvinyl chloride . 

A very similar effect of the surface concentration on the conformation of adsorbed macromolecules was observed by Cohen Stuart et al. [25] who studied the diffusion of the polystyrene latex particles in aqueous solutions of PEO by photon-correlation spectroscopy. The thickness of the hydrodynamic layer 8 (nm) calculated from the loss of the particle diffusivity was low at low coverage but showed a steep increase as the adsorbed amount exceeded a certain threshold. Concretely, 8 increased from 40 to 170 nm when the surface concentration of PEO rose from 1.0 to 1.5 mg/m2. This character of the dependence is consistent with the calculations made by the authors [25] according to the theory developed by Scheutjens and Fleer [10,12] which predicts a similar variation of the hydrodynamic layer thickness of adsorbed polymer with coverage. The dominant contribution to this thickness comes from long tails which extend far into the solution. 

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