Kinetics of Activation of Carboxyls to Succinimidyl Ester Groups in Monolayers Grafted on Silicon: An in Situ Real-Time Infrared Spectroscopy Study

Abstract

The kinetics of activation reaction of acid-terminated monolayers grafted onto crystalline (111) silicon surfaces with N-ethyl-N′-(dimethylaminopropyl)-carbodiimide in the presence of N-hydroxysuccinimide is investigated using in situ real-time infrared spectroscopy. In the case of fully acid-terminated surfaces, the results show that the reaction rate exhibits a biexponential law, with two characteristic times, a fast one, τ1, and a slow one, τ2. The τ1 and τ2 values depend on temperature and solution composition. Moreover, the reaction pathways related to τ1 are partially suppressed for mixed monolayers, that is, by lowering the density of acid sites. These observations are discussed within the framework of a reaction mechanism.