Adsorption of Polyethyleneglycol at the Mercury/Solution Interface

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Abstract The adsorption of polyethyleneglycol (PEG) was investigated at the mercury/solution interface by the observation of the differential capacity and the inhibitive action on the deposition of cadmium or copper. From the differential capacity measurements, the adsorption of PEG was found to be controlled by the diffusion of the adsorbate to the dropping mercury electrode under the present experimental conditions. The relation between the time required to attain the saturated adsorption and the bulk concentration (a) was explained approximately by the Koryta equation, though its deviation from the Koryta equation was somewhat larger than that for polyvinylpyrrolidone. When the maximum surface concentration and the mean molecular weight of PEG were expressed by Γm and \barM respectively, the plot of logΓm-log\barM revealed two linear parts crossing each other at \barM=ca. 600. The slope for \barM≥600 was ca. −1, which implied the relation of “\barM·Γm=const.”, i.e., the segment numbers of PEG molecules adsorbed per unit area were constant, independently of \barM, in the region of \barM≥600. The configuration of PEG of \barM<600 at the interface was considered to be different from that of PEG of \barM≥600 because the slope for \barM<600 was different from that for \barM≥600. From the polarographic current measurements i.e., the inhibitive effect on the reduction of Cd2+ or Cu2+), the time (tmi) needed to achieve the maximum inhibition was obtained; it was then compared with that obtained from the capacity data. The relation of “loga=(−1⁄2)logtmi+const.” based on the Koryta equation was approximately applicable to the cases with a relatively large \barM value.