| Recently the concept of Langmuir-Blodgett (LB) film "gluing" was introduced, which is the ionic crosslinking of a surfactant monolayer with polyelectrolyte in the subphase. The resultant glued films have increased gas permeation selectivity and robustness. In this dissertation, a series of fluorinated surfactants and their resultant properties were studied, with particular emphasis on monolayer, bilayer gas permeation, and surface-coating properties.;Permeation measurements have been made for He, O2, CO 2 and N2 across single Langmuir-Blodgett (LB) bilayers derived from 1,2,4,5-tetrakis[(N-(undecanoamidoethyl)-N,N -dimethyl ammonium) methyl]benzene tetrabromide (4H10) and 1,2,4,5-tetrakis [(N-(perfluoroundecanoamidoethyl)- N,N-dimethyl ammonium)methyl]benzene tetrabromide (4F10) in the absence and in the presence of entrapped polyelectrolyte. For bilayers glued with poly(acrylic acid) (PAA), single LB bilayers of 4F10 show a higher permeance for He and N2 but a lower permeation rate of CO2, as compared with an analogous LB bilayers made from 4H10. The relatively low permeation rate of CO2 for the former has been attributed to reduced associative interactions with the fluorocarbon-rich bilayer. These results, together with the fact that glued bilayers of 4H10 (having a thinner PAA layer as compared with those made from 4F10) exhibit lower He and N 2 permeances, provide compelling evidence that the main barrier for gas transport is the combination of surfactant plus PAA, and not simply the polymer glue layer.;In a separate study the Langmuir-Blodgett deposition of a single monolayer of 4F10 onto a thin film made from alternating layers of poly(diallydimethylammonium chloride) (PDADMA) and poly(4-styrenesulfonate) (PSS) ions affords a uniform, fluorinated surface of low energy. An analogous surface that has been constructed by self-assembly shows the same critical surface tension of 16.5 dyn/cm. Comparison of Zisman plots for these two modified films, in combination with analysis by X-ray photoelectron spectroscopy, indicates that Langmuir-Blodgett deposition produces a higher quality and more densely-packed fluorocarbon surface that is very hydrophobic. In sharp contrast, the use of a single-chain analog (i.e., N-(perfluoroundecanoamidoethyl) N,N,N-trimethylammonium bromide) (1F10) affords relatively high energy surfaces by Langmuir-Blodgett deposition and by self-assembly. |
