An AFM Study of the Effects of Silanization Temperature, Hydration, and Annealing on the Nucleation and Aggregation of Condensed OTS Domains on Mica.

Partial monolayers of octadecyltrichlorosilane (OTS) were formed on mica under different reaction conditions in which the silanization temperature, time, and amount of water adsorbed on the mica substrates were varied. OTS surface coverage increased with silanization time for all samples; however, the amount and distribution of adsorbed OTS varied greatly under these different reaction conditions. AFM analysis showed that OTS formed two phases on mica silanized at 25°C: condensed "island-like" domains and expanded "liquid-like" domains. Partially dehydrated mica silanized at 9°C, however, displayed only condensed domains which were of smaller size compared to those on the 25°C samples. The lateral diffusion and aggregation of small condensed OTS domains to form larger aggregates was evident on all surfaces except the 25°C partially dehydrated mica. A uniform distribution of many small condensed domains surrounded by expanded OTS phases was seen instead. Extended annealing resulted in surface diffusion and aggregation of these domains and nucleation of new condensed domains from the surrounding expanded OTS phases. These observations are consistent with a deposition, diffusion, and aggregation model (DDA) which allows for activated diffusion; however, rigorous modeling is not presented here.