Abstract:

The self-assembled monolayers (SAMs). which were prepared by spontaneous adsorption of cysteamine on gold surface, were characterized using contact-angle titrations. Contact-angle titration data acquired for the cysteamine SAMs exhibited a smooth transition in contact angle between plateau regions at low and high pH value. The surface pK_b, was estimated to be 1.8±0.2, much lower than that in solution. The electroactive azobenzene group was anchored to the monolayer via amide surface reaction. Thus the formed SAMs were further subjected to exchange in dilute pentanethiol soluition. At each stage of modification, the surface was monitored by con-tact-angle titration and cyclic voltanimetry. It was found that the titration curves obviously shifted to the higher contact-angle direction with the increase of surface hydrophobicity. The results are in good agreement with the cyclic voltammetric measurements, demonstrating that the contact-angle titration is a useful technique for monitoring the step by step surface reactions.

Key words: Cysteamine self-assembled monolayers (SAMs), Contact-angle titration, Step-by-step surface reaction