Carbamate Chemistry at Interfaces: Practical Considerations and Challenges of Studying Amine Surfactants
Journal article, 2019
It is well known that CO2 reacts with primary and secondary amines in aqueous solutions and forms carbamates. This reaction can have consequences when studying the self-assembly of amines. In this article, we discuss the practical challenges when working with an alkyl Y-shaped amine (Y12-amine) and demonstrate how the formation of carbamate species influences the physicochemistry of the amine-based surfactant. A drift in dynamic surface tension was observed for Y12-amine at pH above pKa due to the reaction with the naturally occurring CO2 from the atmosphere. The drift in dynamic surface tension was more pronounced at pH above pKa, than at and below pKa. Furthermore, the drift in dynamic surface tension of Y12-amine at pH 12 also affected the surfactant's critical micelle concentration (CMC). CMC of Y12-amine determined by the pendant drop at the air/water interface was almost five times higher than at the N-2/water interface. The latter result was in agreement with the one determined by monitoring the change in chemical shift of H-1 NMR in a N-2 atmosphere. Moreover, it was also shown that the adsorption of the amine at different interfaces influences carbamate formation.
Dynamic surface tension