Understanding the Deposition and Molecular Interaction Mechanisms of Substrate-supported Functional Coatings

• Author / Creator

  Huang, Jun

• Functional coatings have been extensively exploited for creating surfaces with desired functionalities in numerous engineering applications, which have received increasing attention over the past few decades. The objectives of this thesis research were to develop stable, hydrophobicity-tunable functional coatings/films and further investigate the deposition and related surface interaction mechanisms using nano-mechanical techniques such as Atomic Force Microscope (AFM) and Surface Forces Apparatus (SFA). The research has focused on four types of surface coatings, including cross-linked hydrocarbon silane (octadecyltrichlorosilane, OTCS) coating, end-grafted hydrophobic polymer (poly(pentafluorophenyl acrylate)-b-polystyrene, PPFPA-b-PS) coating, layer-by-layer deposited polyethyleneimine (PEI) and PPFPA-b-PS multi-layer coating and mussel inspired polycatecholamine (polynorepinephrine, pNE) coating. This research has revealed that the deposition process of OTCS on substrate surface with few active sites (e.g., freshly cleaved mica) via a facile vapor deposition method mainly contains two stages: silane molecules first react with the limited silanol groups forming a smooth layer and then the initial layer can serve as nucleation sites for further deposition to form cross-linked hydrocarbon coatings. The interaction forces between the as-obtained silane-functionalized mica surfaces were quantitatively measured using an SFA. It was found that the approaching force-distance profiles of the OTCS surfaces obtained via a shorter deposition time (e.g., 2 h, 8h) could be reasonably described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, for the OTCS surfaces obtained via longer deposition times (e.g., 48 h), the hydrophobic interaction and steric interaction play an important role due to their enhanced surface hydrophobicity and surface roughness. The obtained results in this work provide useful insights into the deposition behaviors of alkylsilanes on substrates possessing low density of reactive sites via vapor deposition method as well as the fundamental interactions of the deposited alkylsilane surfaces in aqueous solutions. A new type of homogeneous, hydrophobicity tunable PPFPA-b-PS polymer coating, covalently end-attached onto mica surface has been developed using a “graft to” methodology via amino group reacting with pentafluoro ester. The interactions between the grafted polymer surfaces in aqueous solutions were measured as a function of separation distance using the SFA technique. The effects of various factors, including surface hydrophobicity, salt concentration and degassing, on the surface interactions were examined. It was found that repulsion dominated the approaching process of PPFPA-b-PS surfaces with low hydrophobicity (water contact angle ~60 degree), while long range attraction (> 50 nm) was detected for surfaces with higher hydrophobicity (water contact angle ~90 degree). The range of measured attraction force decreases at high salt concentration or after degassing, which shows strong correlation between nano-bubbles or gas layers present on the hydrophobic PPFPA-b-PS surface (water contact angle ~ 90 degree) and their long-range attraction. These experimental results help to better understand the interaction mechanisms between stable polymer surfaces in aqueous solutions, with implications for engineering processes such as mineral flotation and protein adsorption. An efficiency way for preparing multi-functional polymeric films based on covalent bonding between active ester polymer, PPFPA-b-PS, and amine-rich polymer, PEI, using spin casting layer-by-layer deposition has been further developed. The film shows switched hydrophobicity and controllable thickness during deposition. The interactions forces between the as-obtained multi-layer films in aqueous solutions were also measured by using the SFA technique under different experimental configurations. Strong adhesion was measured between PEI and PPFPA-b-PS, which shows significant stretching behavior before the two surfaces were separated. Importantly, a facile method has been developed for preparing robust freestanding polymeric films by peeling off the polymer films from silicon substrates, which show good transparency, excellent mechanic property and excellent stability in high salt and organic solvent. This study demonstrates a versatile route for preparing multi-functional polymeric surfaces based on active ester and amines. Finally, a systematically study about the effect of amine groups on the polymerization and surface interaction of mussel-inspired polycatecholamine coatings (e.g., pNE) in aqueous solutions has been conducted. Our surface-force results based on those smooth pNE surfaces indicate that the adhesive strength between pNE layers is thirty times higher than that of a poly(pyrocatechol) coating without any amine moiety at the same polymerization time. The significant improvement of adhesion after introducing primary amine has proved that primary amine group is a vital factor in the design and development of mussel-inspired catechol-coating materials.

• Subjects / Keywords

  • Molecular Interaction
  • Functional Coatings
  • Surface Forces

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3F766M9G

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.