ADSORPTION-KINETICS OF ALKANETHIOLS STUDIED BY QUARTZ-CRYSTAL MICROBALANCE

The quartz crystal microbalance (QCM) has been employed extensively fo r measurement of mass changes at metal surface while the metal coated electrode is immersed in a liquid. We report the real time in-situ ads orption kinetic trends of alkanethiol CH3(CH2)(n-1)SH (n = 8, 12, 16) monolayers with different chain lengths and solvents using QCM. Regard ing 1-octanethiol monolayer formation on gold surface, we could identi fy the two distinct monolayer formation steps in hexane and ethanol so lutions. The adsorption process of alkanethiols is characterized by tw o distinct steps. In the kinetically controlled initial monolayer form ation step, the adsorption rate of short chain alkanethiols is faster than that of long chain alkanethiols. The second step is a thermodynam ically controlled ordering and packing process. In case of short chain alkanethiols, these two separated adsorption steps were clearly obser ved, but in the case of long chain alkanethiols (over 10 carbon number s) only one step of monolayer formation was observed. (C) 1998 Elsevie r Science S.A. All rights reserved.