Studying silane mobility on hydrated mica using ambient AFM

The mobility of the mono-functional aminosilane, aminopropyldimethylmethoxysilane (APDMMS), on mica has been investigated under ambient relative humidity (RH) using tapping-mode (TM) AFM. Silane layers were formed from vapour phase at various, controlled humidities and then imaged at ambient laboratory conditions (typically 30-40% RH). At low RH of formation (<25%) films without any resolvable sub-structure were formed, and these were stable to the imaging probe. At high RH of formation (>25%), where islands of phase II water are known to exist on mica, a two-phase domain structure was seen as two height levels and the surface area of the higher domains correlated with the RH. Sequential images taken over a 30-60 min time period show that these domains are mobile and at intermediate to high RH the domains coalesce under the influence of the scanning AFM tip. The results suggest the APDMMS resides at the air-water interface (rather than interacting with the mica) and that it preferentially interacts with the mobile phase II water as opposed to the phase I water tightly bound to the mica.