Physisorption and chemisorption of a self-assembled monolayer by the quartz crystal microbalance.

A new adsorption model was developed to investigate the adsorption process of SAMs in the gaseous scenario, and the results were verified by using a prototype quartz crystal microbalance (QCM) sensor. In the experimental study, the observed properties in the gaseous scenario did not conform to the conventional theories well but matched the proposed adsorption model better. Hence, an optimal methodology for the theoretical study of adsorption process of SAMs was developed. The conventional adsorption model of Langmuir is suitable only for the fast initial adsorption step (i.e., physisorption) in the process of forming SAMs in the liquid scenario. Here, the rates of adsorption and desorption (ka, kd) at different temperatures were investigated. The activation barrier Ea = 59.738 kJ/mol was obtained by the Arrhenius equation. The result agreed well with that obtained experimentally. More importantly, this study has established a new avenue of QCM chip applications.