engleski

The simple electrochemical method for detection of 3d molecular reorientation in adsorbed layer of organic substances

Reorientation of initially flatly adsorbed molecules to slant or fully erected position on the electrode surface seems to be a common transition during adsorption of organic substances. However, the reorientation is not easily detected and its occurrence often questioned. In this paper we present a simple electrochemical method to detect 3d molecular reorientation at the electrode surface. The method is based on ac voltammetric measurement of a rate of change of capacitive current, dIc/dt with time, during the adsorption process, that is qualitatively different for adsorption with reorientation in respect to that without it. The theoretical considerations of simple, diffusion-controlled adsorption without reorientation predicts monotonic decrease of dIc/dt curve. This is experimentally demonstrated in the adsorption of nearly isotropic 1-aminoadamantanehydrochloride (ADA). Contrary to this theoretical prediction it is shown that in the cases when the orientational ordering and reorientation takes place the rate of change of capacitive current vs. time exhibits a plateau followed by steep decrease. Such behavior is demonstrated experimentally in adsorption of anisotropic, rod-like Triton-X-100 molecule. This has previously been shown that undergo reorientation during the adsorption process. Qualitatively the same behavior of dIc/dt was observed for both molecules in a case of diffusion controlled adsorption as well as adsorption from stirred solution.

adsorption; reorientation; capacitance; time; T-X-100; adamantane derivative

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