Hydrodynamic influence on the fractal morphology of the linoleic acid adsorbed layer at the mercury/electrolyte interface

Fractal morphology of the adsorbed layer of linoleic acid has been studied for two adsorption regimes: diffusion controlled and mass-transfer controlled adsorption in a stirred solution. The study has been conducted using ac voltammetry in combination with size scaling of the hanging mercury drop electrode for determination of the adsorbed layer fractal dimension. It has been found that morphology of the linoleic acid adsorbed layer, as given by the fractal dimension, is a result of growth mechanism which is influenced by hydrodynamics (stirring or diffusion) and by the structure of the solution (monomers, dimers). At a lower fractional electrode coverage the adsorbed layer structure is primarily governed by the adsorption mechanism details. Fractal structure for high fractional electrode coverage is determined by geometrical constraints. For the purely diffusion controlled adsorption process, the mechanism of the adsorbed structure growth is determined by the solution structure. This is manifested in fractal dimensions D≈2.2 and D≈2.5, corresponding to the cluster–cluster and particle–cluster growth mechanisms, respectively. In a stirred solution, dominant influence on the growth mechanism of the LA adsorbed layer comes from shear, resulting in the same fractal dimension (D=2.44) throughout the entire investigated concentration range (accumulation times).