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The general applicability of the Stokes-Einstein relation for diffusion has been studied for the case of cyclohexylbromide diffusing in n-alkanes with special reference to the size relationship between the solute and solvent molecules.The plot of Do against l/qo (Do = mutual diffusion coefficient at infinite dilution, yo = solvent viscosity) yields two straight lines with their point of intersection at about n-nonane (C9). This appears to conform with a more generalized form of the Stokes-Einstein theory also taking into account particle size and molecular conformation for solvent molecules of increasing chain length.' A. Einstein, Investigations on the Theory of the Brownian Movement, ed.

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Measurements of translational diffusion coefficients of oligosaccharides have been made as a function of temperature in a dilute hydroxyethylcellulose gel swollen in water, dimethyl formamide (DMF) and dimethyl sulphoxide (DMSO). The diffusion coefficients in the gel phase are substantially lower than the values for free diffusion in the bulk solvents in all cases. The influences of solvent character, temperature and polymer concentration on this reduction are discussed.Fluorescence depolarisation measurements were made over a corresponding temperature interval in the same gel system using fluorescein freely dispersed in the gel phase and also conjugated to the matrix polymer. The results are discussed in terms of the microscopic viscosities of the systems.