Synthesis, reactivity, and characterization of thin organic films on metallic substrates
Abstract
We investigated thin films of 3-aminopropyltriethoxysilane (APS), 3-glycidoxypropyltrimethoxysilane (GPS), 3-methacryloxypropyltrimethoxysilane (TPM), trimethoxyvinylsilane (VS), tetraethoxysilane (TEOS), 3-bromopropyltrimethoxysilane (BPS), and 3-mercaptopropyltrimethoxysilane (MPS) adsorbed on aluminum or gold substrates with reflection-absorption infrared spectroscopy (RAIR), optical ellipsometry, wetting measurements, and by gravimetric analysis with the quartz-crystal microbalance (QCM). We present optical response functions in the infrared region and simulations of isotropic RAIR-spectra of these compounds. Thin films were prepared by vapor adsorption of the silane on the substrate. RAIR-spectroscopy, ellipsometry, gravimetric analysis, and wetting behavior results are consistent with approximately monolayer coverage and a preferential orientation of the molecules on the surface. The adsorption and the final surface loading levels, varying from 3 to 7 molecules per nm$\sp2$, are affected by the hydrolysis and condensation reactions of the siloxane moieties, as indicated by gravimetric analysis. We studied the reactivity of thin layers of APS, MPS, BPS, and 8-bromooctyltrimethoxysilane (BOS). We observed stoichiometric reactions of APS with chlorodimethylsilane and of MPS with phenylmercuryhydroxide to give $\rm\lbrack -Si(CH\sb2)\sb3NH\sbsp{2}{+}SiMe\sb2H\rbrack Cl\sp-$ and $\rm\lbrack -Si(CH\sb2)\sb3SHgPh\rbrack$, respectively. We observed no substitution reactions in thin films of BPS and BOS. In this case, the reactions may be obstructed by steric congestion of the surface-immobilized reaction centers. Thin layers of polyethylenimine (PEI), crosslinked with a diepoxide resin, were immobilized on surfaces modified with GPS. Temperature and pH-dependent cyclovoltammetry indicates good durability of these surfaces in the range from 25$\sp\circ$ to 100$\sp\circ$C and pH 3 to 9. Polyelectrolytes, derived from 1.4-diazabicyclo (2.2.2) octane and 1.4-dibromobutane, were attached on surfaces modified with APS or PEI.
Degree
Ph.D.
Advisors
Bein, Purdue University.
Subject Area
Chemistry
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