Adsorption of long-chain electrolytes from aqueous solution on graphite of known area and on polystyrene

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The adsorption isotherms of sodium dodecyl sulfate and potassium myristate on ash-free graphite of known area have been determined at 30°C. and 35°C., respectively. The experimental methods are discussed in some detail. Calculations, based on two extreme assumptions concerning the concentration of solvent in the surface region, yield values of the specific adsorption which differ by less than the experimental errors of the observations. The isotherm of sodium dodecyl sulfate exhibits a discontinuity at the critical concentration for micelle formation; it is possible that a similar discontinuity occurs in the myristate isotherm. Both isotherms pass through a maximum at equilibrium concentrations above the critical concentration. The adsorption of sodium dodecyl sulfate on polystyrene has been measured over a short concentration range; the specific area of this solid is not known with any degree of precision. This isotherm also exhibits a maximum at approximately the same equilibrium concentration at which a maximum in the isotherm of the same salt on graphite occurs. The areas per adsorbed molecule have been calculated for sodium dodecyl sulfate and potassium myristate on graphite as a function of the equilibrium concentration of electrolyte. The minimum area per molecule is 51.0 A2 for the sulfate and 36.6 A2 for the myristate.


This article was originally published in Journal of Colloid Science. The full-text article from the publisher can be found here.

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Journal of Colloid Science