Date of Award

12-2004

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

David J. Neivandt

Second Committee Member

Carl P. Tripp

Third Committee Member

Paul J. Millard

Abstract

The ability to template polymeric species in monolayers of highly ordered surfactant has been studied using Infrared Attenuated Total Reflection (IR-ATR) spectroscopy. The cationic surfactant used in this study, cetyltrimethlyamrnonium bromide (CTAB), is known to form a highly ordered layer when adsorbed onto a silica surface from solution at very low concentration and elevated pH. Introduction of an anionic polymeric species has been shown to remove surfactant from the surface via electrostatic complexation leaving an imprint in the residual surfactant layer. This imprint is assumed to be unique to the given anionic polymer's conformation, charge distribution and charge density. Potential usage of these unique imprints may be found in many areas, perhaps most interestingly, in the area of biosensor technology. This thesis presents work aimed at developing a way of utilizing this to produce enhanced specificity in biosensors. It has been shown that the imprints are transient; as such to make use of them in creating the template it is necessary to further modify the surface to make them permanent. It is believed that the residual surfactant exists in highly populated islands that help to retain the high degree of conformational order through entropic interactions. These islands surround the imprint sites, which are bare spots on the silica surface and therefore must be refilled to make the imprint permanent as well as to introduce a complementary charge. This was done using a gas phase reaction of an aminopropyl silane, aminopropyldimethylethoxy silane (APDMES), with the bare silica surface. The covalently bound APDMES holds the imprint shape on the surface and allows for further surface modifications. Additionally, the APDMES is terminated with a cationic amine group that provides an electrostatic driving force for re-adsorption of the polymer. The residual electrostatically-bound CTAB was removed by simply wiping with an organic solvent (chloroform), leaving a bare surface except for the permanently bound APDMES. The surface was then treated in situ with an alkoxy silane that reacts with the exposed silica surface and backfills around the APDMES. This silane has a longer alkyl chain than the APDMES, thus it essentially "buries" the APDMES amine groups below the level of the alkoxy silane. The covalently bound silanes create the permanent form of the desired template. Reintroduction of the target species, it was assumed, would result in the adsorption of the species onto the cationic target sites. This adsorption would potentially be monitored via the characteristic IR resonances of the target species.

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