Inorganic-Organic Sol-Gel Derived Hybrid Materials as Abrasion Resistant Coatings
Inorganic-organic hybrid materials have been developed using sol-gel reactions of a
trialkoxysilylated organic compound and a metal or semi-metal alkoxide and applied as coatings
on polymeric or metallic substrates. Many of these coatings have demonstrated good to excellent
Abrasion resistant coatings were prepared by hydrolysis and condensation of mixtures of
a triethoxysilylated diethylenetriamine (f-DETA), tetramethoxysilane (TMOS), water and an
alcohol in the presence of an acid catalyst (a one-step hydrolysis approach). The influences of
many formulation and processing variables on the gelation time, optical properties, hardness and
abrasion resistance were investigated. An aminolysis mechanism was also proposed to explain
the adhesion between sol-gel derived coatings and polycarbonate substrates promoted by a 3-aminopropyltriethoxysilane (3-APS) primer. FT-IR, GPC, 1H and 13C NMR, XPS experiments
were conducted to support this mechanism.
The f-DETA/TMOS system is essentially a binary system of an alkyltriethoxysilane (T)
and a tetraalkoxysilane (Q). At pH 0-2 and pH 4-5, the relative condensation reactivities of the T
and Q species in this system were compared using 29Si NMR spectroscopy. After thermal
curing, 13C or 29Si solid state NMR spectroscopy was used to estimate the extent of hydrolysis
of the urea linkages in f-DETA, the concentration of residual alkoxysilane groups, and the extent
of condensation for both T and Q species. The dependence of the morphology of f-DETA/TMOS
gels on the pH and the water concentration was also investigated using AFM, SEM and SAXS.
Many other trialkoxysilylated organic compounds containing urea, urethane, epoxy and
siloxane linkages were also synthesized and utilized to prepare abrasion resistant coatings via a
one-step hydrolysis approach, a two-step hydrolysis approach or a moisture-curing approach.
Coatings derived from many of these systems or approaches demonstrated abrasion resistance
comparable to that of the f-DETA/TMOS coating. Thin coatings were also derived from cubic
octasilicate monomers via hydrosilylation or sol-gel reactions. These coatings were very
transparent but unfortunately lacked abrasion resistance.
Advisor:Thomas C. Ward; John G. Dillard; Judy S. Riffle; Richey M. Davis; Garth L. Wilkes
School:Virginia Polytechnic Institute and State University
School Location:USA - Virginia
Source Type:Master's Thesis
Date of Publication:08/04/1999