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" Precise Tuning of Surface Properties by Degrafting Organosilanes for Evaluation of Interfacial Phenomena "
Miles, Jason Robert
Yingling, Yaroslava
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Latin Dissertation
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English
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| Record Number
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1106211
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TLpq2381672881
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| Main Entry
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Miles, Jason Robert
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Yingling, Yaroslava
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| Title & Author
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Precise Tuning of Surface Properties by Degrafting Organosilanes for Evaluation of Interfacial Phenomena\ Miles, Jason RobertYingling, Yaroslava
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| College
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North Carolina State University
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| Date
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2019
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| student score
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2019
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| Degree
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Ph.D.
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| Page No
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128
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| Abstract
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The ability to modify physical and chemical characteristics of surfaces and interfaces is important to achieve desired wetting, adsorbing, releasing, and adhesive properties. Organosilanes are among the most commonly used materials for the modification of surface properties, with their ability to undergo a rapid condensation reaction with hydroxyl groups present on oxide surfaces. The increased use of composite materials and the decreased feature sizes present on devices requires a greater degree of control over the density and distribution of functional groups on the surface than was possible to achieve by the deposition of organosilanes. The primary goal of this Ph.D. dissertation is the development of a surface modification technique that allows for precise control over surface energy and chemistry along with the ability to impart multiple functionalities on the surface to control more complex interfacial phenomena. We prepare silica surfaces functionalized with homogeneous silane SAMs by solution and vapor phase deposition approaches. The degrafting of silanes from these surfaces, using tetrabutylammonium fluoride (TBAF), allows for the precise tuning of the fractional coverage of silanes on the surface while maintaining a uniform surface coverage and regenerating surface hydroxyl groups. We can generate substrate-bound gradients of fractional coverage of silanes with tunable profiles over the desired length scale. We model the kinetic of TBAF degrafting by a series of first-order rate equations, with initial conditions that are dependent on the binding structure of the silanes at the surface. Mono-functional silanes exhibit a single exponential decay in their degrafting profiles as they can only form one bond with the surface. Tri-functional silanes exhibit a delay in degrafting as they form multiple surface and in-plane bonds, and the silanes connectivity to the surface must completely break before their removal from the surface. By comparing the degrafting profiles of various silane SAMs to those predicted by the kinetic model, we probe the binding structure of the silane at the surface to gain insight into the stability of the SAM. Silane SAMs deposited from the vapor phase undergo faster degrafting than those deposited from a good solvent, indicating that the SAMs formed from vapor consist of more loosely packed arrays with less in-plane connectivity. Alkyl silanes deposit on surfaces in a mogul-like structure due to geometric constraints, leading to a large amount of in-plane condensation relative to the amount of condensation with surface hydroxyls. The mogul-like structures accelerate the rate of degrafting. In comparison, fluorinated silanes have a larger van der Waals diameter that limits the amount of in-plane condensation and favors condensation with the surface. Silanes with short alkyl backbones or ones that exhibit favorable interactions of the functional group with the surface, lead to poor alignment and rapidly degraft due to their highly aggregated structures. We use these silane functionalized surfaces to investigate the adsorption and covalent attachment of stimuli-responsive elastin-like polypeptides (ELPs) to silica surfaces. ELPs show significant adsorption onto surface energy gradients and the presence of a strong denaturant allowed for partial removal of the peptides, with more desorption occurring from the hydrophilic end of the gradient. We attempted the covalent attachment of ELPs to silane functionalized surfaces exhibiting anhydride and glycidyl ether functionalities. Attachment to anhydride functionalized surfaces resulted in similar surface morphology to that of physical adsorption. However, attachment to glycidyl ether functionalized surfaces resulted in distinct features present on the surface. Grafted homopolymer ELPs exhibited limited stimuli-responsive behavior when heated above their bulk transition temperature, ~29-35°C. The use of TBAF degrafting, to control the density of grafted ELPs and for minimizing physical adsorption, is promising for future studies involving the attachment of peptides to surfaces while maintaining their functionality.
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Chemical engineering
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