Semester

Fall

Date of Graduation

2011

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Darran R Cairns

Abstract

The primary goal of this research was to synthesize water- and oil-repellent coatings that offer sustained functionality and durability. Engineered low surface energy materials generally suffer from a lack of mechanical robustness, which makes them susceptible to damage by abrasive wear. Fluorinated silanes are often combined with alkoxide precursors via sol--gel co-condensation to create coatings with high hardness and good substrate adhesion. However, a common problem with these materials is that the organic moieties that provide low surface energy also become surface segregated and highly concentrated at the solid-air interface. With such a structure, mechanical removal of the top surface by abrasion, for example, reveals subsurface areas that are then much less concentrated in terms of functional chemistry. The material developed in this study was designed to overcome this problem by means of a tailored and templated mesostructure that effectively encapsulated the low surface energy functional moieties, and thus achieves sustained functionality during abrasive wear. This material, applied as a thin coating to a variety of substrates, has the potential to reduce waste and pollution and the environmental degradation of materials and structures. Improving the performance of such materials can benefit a wide variety of applications. These include optoelectronic devices including photovoltaic panels; automobile and aircraft; architectural structures; the chemical, food, and medical industries for hygienic and anti-fouling requirements; textiles; and household applications. This approach has further implications in areas such as boundary lubrication and drug delivery systems.;Hydrophobic-oleophobic mesoporous fluorinated silica films were synthesized via sol-gel co-condensation and coated on glass substrates. Fluorosilane and surfactant template concentrations were varied to elucidate the effect of organic functionality and porosity on performance. Structural, chemical, mechanical, surface, and tribological properties were investigated to examine the performance of functionalized mesostructured thin films in abrasive environments. Analytical techniques included XPS depth profiling, porosimetry, AFM and friction force microscopy, nanoindentation, contact angle goniometry, and stylus profilometry. Controlled abrasion was conducted using a lab-built instrument. Hydrophobic and oleophobic properties were monitored ex-situ during abrasion to observe and quantify changes in functionality as the material is worn.;Experimental results show that surfactant templating aids in generating an internal mesostructure that facilitates encapsulation of functional moieties. This encapsulation allows exposed surfaces to be sacrificially worn away while maintaining much of the original functionality. The results of tribological measurements, as observed through abrasive wear testing, friction force mapping, and wear rate calculations, suggest that the low-friction surface generate by fluorosilane moieties grafted to internal pore surfaces mitigates to some extent the detrimental effect of film porosity on hardness and wear resistance.

Download

Share

COinS