GROWTH OF COMPACT LAYERS AT THE INTERFACE .3. SURFACE AGGREGATION OF ALPHA-CYCLODEXTRINS AND GAMMA-CYCLODEXTRINS IN AQUEOUS-SOLUTIONS OF POTASSIUM FLUORIDE

Adsorption of both alpha- and gamma-cyclodextrins (CDs) on the mercury elect-rode interface leads to a compact layer formed by the nucleatio n/growth mechanism. Measurements of the admittance versus time were us ed for elucidation of the growth mechanism. The layer of alpha-cyclode xtrin is formed by a two-dimensional instantaneous nucleation in almos t the entire adsorption region, with the exception of potentials near the edge of the capacitance 'pit'. The growth of the gamma-cyclodextri n layer cannot be described by Avrami formalism due to a mixed growth mode yielding much higher time exponents. Long time measurements revea l considerable growth anomalies interpreted as a further contraction o f originally irregular islands of a condensed phase. The observed time effects correlate with literature data on aggregation of CDs investig ated by STM and light scattering. (C) 1997 Elsevier Science S.A.