Date of Degree

2-2020

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Alan M. Lyons

Committee Members

Alexander Greer

Chwen-Yang Shew

Subject Categories

Polymer Chemistry

Keywords

surface coatings, hydrophobic coatings, PV solar glass, anti-soiling, self-cleaning, anti-reflective

Abstract

Anti-reflective, anti-soiling and self-cleaning coatings are currently of interest for photovoltaic (PV) cover glass applications due to their potential to increase the amount of light transmitted through the glass and improve efficiency by reducing the number of contaminants bound to the surface of the glass (soiling). Naturally occurring dew is known to exacerbate soiling via cementation of dust on the glass surface. To address these challenges, fluorinated ethylene-propylene (FEP) polymer coatings were formed on solar cover glass using a lamination-peeling technique. This process forms a thin (thick) polymer coating on the glass with a nano-texture that can be controlled by modifying the lamination-peeling process conditions.

Anti-reflective properties of the nano-coating were achieved by using a low refractive index polymer. Moreover, the morphology of the coating creates a refractive index gradient further reducing the effective refractive index. The anti-soiling and self-cleaning properties were achieved due to the surface’s low chemical reactivity and stable hydrophobicity. Self-cleaning performance was increased by forming a hybrid surface where hydrophilic domains, formed by selectively removing the hydrophobic polymer to expose the underlying hydrophilic glass substrate, accelerated condensation of atmospheric water vapor. Characterization of the coating morphology was performed by atomic force microscopy (AFM), and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical bonding between the fluoropolymer coating and the underlying soda-lime glass.

The anti-soiling and self-cleaning properties of the coatings were evaluated using laboratory soiling tests in the presence of condensed water. These tests were designed and built to mimic natural soiling conditions, with a focus on soiling in the presence of simulated dew. Automation of experimental equipment and self-cleaning analytical methods was done by implementing microcontrollers and computer vision assisted algorithms respectively. Laboratory soiling and cleaning experiments conducted on fluoropolymer coated PV grade cover glass revealed a novel “dust herding” anti-soiling mechanism along with improved self-cleaning abilities. Hybrid hydrophobic-hydrophilic surfaces enhanced the self-cleaning effect in the presence of various soil types.

Nanotextured fluoropolymer coatings were also fabricated on aluminum substrates. These surfaces exhibited stable coalescence-induced drop jumping under atmospheric pressure, which proved stable for 1000 hours at elevated temperature and humidity conditions (saturated vapor 50 K above the surface temperature). Jumping rates and stabilities were correlated with surface morphology. This phenomenon may prove useful for self-cleaning surfaces, as well as enhanced heat transfer for applications in electronic packaging and thermal power plant production of electricity.

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