Abstract: The characteristic change of surface wettibility of cysteamine self-assembled monolayers was reported. Contact angle titration method was used to carry out the real time measurements of the surface wettibility of the monolayers which were formed by dipping gold substrate into dilute HSCH₂CH₂NH₂/CH₃CH₂OH solution. After the monolayers transfered from solid/liquid interface to solid/air interface, the contact angles of the monolayers underwent a sharp increase, then got down to a slow variation process. From the perspective surface free energy, the structural rearrangement of monolayers was considered as the main reason for such a phenomenon. The contact angle titration curve for basic group tailored SAM swas obtained by using a series of solutions with different pH values. The pK_b value of cysteamine SAM swas derived to be 1.7±0.2. Based on above characterization, the change of surface wettibility for the monolayers was further studied at a long time scale by taking account of changes in pK_b and △θ (difference between two plateaus of the contact angle titration curve).

Key words: Cysteamine, Self-assembled monolayer films, Contact angle titration, Surface pK_b