Title page for ETD etd-080299-155954


Type of Document Dissertation
Author Li, Chenghong
Author's Email Address ningxian@vt.edu
URN etd-080299-155954
Title Inorganic-Organic Sol-Gel Derived Hybrid Materials as Abrasion Resistant Coatings
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Wilkes, Garth L. Committee Chair
Riffle, Judy S. Committee Co-Chair
Davis, Richey M. Committee Member
Dillard, John G. Committee Member
Ward, Thomas C. Committee Member
Keywords
  • Abrasion Resistant Coatings
  • Inorganic-Organic Hybrid Materials
  • Optical Plastics
  • Sol-Gel Processes
Date of Defense 1999-07-19
Availability restricted
Abstract
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 resistance.

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.

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