Kinetics of activation of carboxyls to succinimidyl ester groups in monolayers grafted on silicon: An in situ real-time infrared spectroscopy study

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.