The Adsorption of Polyvinylpyrrolidone at the Mercury/Solution Interface

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Abstract
The adsorption of polyvinylpyrrolidone (PVP), known as a water-soluble polymer, at the electrolyte/DME interface was examined by observing the differential capacity vs. the time relation, under conditions where the adsorption process was mainly controlled by diffusion. In the case of a relatively low bulk concentration and a short adsorption time, the adsorption rate of PVP at−500 mV(SCE) was controlled almost wholly by the diffusion of the adsorbate to the DME. The relation between the time required to attain the saturated adsorption and the bulk concentration was explained approximately by the Koryta equation, based on the linear diffusion. PVP showed no tendency to form multi-layers within the range of bulk concentrations and adsorption times observed. The maximum surface concentration of PVP decreased almost linearly with the increase in its mean molecular weight. The number of constitutive segments adsorbed per unit of area to form a monolayer at the interface was almost constant, independent of the mean molecular weight. The activation energy for the diffusion was found to be ca. 4.7 kcal/mol. On the basis of the results obtained, the configuration of PVP adsorbed at the interface was discussed.