Studies on interfacial behavior and structural transformations in a reacting monolayer system

The network formation in trialkoxysilane monolayers at the air-water interface has been the focus of contention over the years. While it can be intuitively assumed that a network architecture is feasible, it is likely that the cross-linking in a 2D geometry may not be as effective as in the bulk due to the geometrical restrictions around the silane functional group. This work attempts to address this issue by investigating the surface behavior and dynamics of film formation in a reacting n-octadecyltrimethoxysilane (OTMS) monolayer system at the air-water interface.; Monolayer studies of OTMS showed that it forms a stable monolayer at the air-water interface. When spread on an acidic subphase, a hydrolysis reaction is initiated and observed to follow a general acid-catalyzed first-order kinetics. The subsequent condensation reactions result in a cross-linked product, as determined from surface rheological experiments consisting of compressional modulus and viscosity measurements. The results of rheological experiments also showed that the cross-linked product exhibited gross behavior similar to a percolating network although the scaling behavior is different from that of the ideal system. Subsequent Brewster angle microscopy determined that the network architecture in this system is loose and dominated by linear segments.; Real time grazing incidence x-ray diffraction (GIXD) studies have shown that OTMS monolayer self-assembles into small domains showing characteristic in-plane ordering of close-packed alkyl chains in a hexagonal lattice. Further GIXD investigations have shown that the short-range positional ordering between the alkyl chains does not significantly change during the course of the reaction.; Overall, the study showed that the network formation is possible in this system although the creation of network junctions is indeed frustrated and inefficient. Considering the results from rheology and x-ray studies, it is speculated that the network junctions are found in the amorphous region and that the ordered domains are primarily made of linear segments and partially reacted OTMS.