Understanding the Deposition and Molecular Interaction Mechanisms of Substrate-supported Functional Coatings by Jun Huang A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Engineering Department of Chemical and Materials Engineering University of Alberta © Jun Huang, 2017 Abstract 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 ii 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 ~60o), while long range attraction (> 50 nm) was detected for surfaces with higher hydrophobicity (water contact angle ~90o). 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 ~ 90o) 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 iii 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. iv Preface This thesis is presented in manuscript based format. Chapters 1, 3, 4, 5 and 6 have been published, submitted, or under preparation for submission as described below. Chapter 1, the section for reviewing hydrophobic interactions has been published in Biointerphases: H Zeng, C Shi, J Huang, L Li, G Liu, H Zhong Recent Experimental Advances on Hydrophobic Interactions at Solid/water and Fluid/water Interfaces, Biointerphases 2016, 11(1), 018903. I was responsible for reviewing the hydrophobic interaction from the aspect of solid/water interfaces as well as the manuscript composition. Chen was responsible for reviewing the part regarding fluid/water interfaces. L Li, G Liu, H Zhong contributed to the manuscript edits. Dr. H Zeng was the supervisory author and was involved in concept formation and manuscript composition. Chapter 3 has been published in the Journal of Physical Chemistry B: J Huang, X Liu, X Qiu, L Xie, B Yan, X Wang, Q Huang, H Zeng Octadecyltrichlorosilane Deposition on Mica Surfaces: The Insight Interface Interaction Mechanism. DOI: 10.1021/acs.jpcb.7b00828. I was responsible for the data collection and analysis as well as the manuscript composition. X Liu, X Qiu, L Xie, B Yan, X Wang, Q Huang, contributed to the manuscript edits. Dr. H Zeng was the supervisory author and was involved in concept formation and manuscript composition. Chapter 4 will be submitted for publication in Journal of Physical Chemistry C: J Huang, X Qiu, B Yan, L Xie, H Zeng End-grafted Hydrophobic Poly(pentafluorophenyl acrylate)-b-Polystyrene Surfaces: Preparation, Characterization and Related Surface Interactions in Aqueous Solutions. I was v responsible for the data collection and analysis as well as the manuscript composition. X Qiu, B Yan and L Xie contributed to the manuscript edits. Dr. H Zeng was the supervisory author and was involved in concept formation and manuscript composition. Chapter 5, a version of this chapter will be submitted for publication in Advanced Functional Materials: J Huang, X Qiu, B Yan, L Xie, H Zeng Multifunctional Polymeric Films Prepared by A Fast and Covalent Bonded Layer-by-Layer Assembly Process. I was responsible for the data collection and analysis as well as the manuscript composition. X Qiu, B Yan and L Xie contributed to the manuscript edits. Dr. H Zeng was the supervisory author and was involved in concept formation and manuscript composition. Chapter 6, part of this chapter has been published in Angewandte Chemie International Edition: C Lim,* J Huang,* S Kim,* H Lee, H Zeng, DS Hwang Nanomechanics of Poly (catecholamine) Coatings in Aqueous Solutions, Angew Chem Int Ed , 2016, 55 (10), 3342. Some of the research conducted for this chapter forms part of an international research collaboration, led by Professor DS Hwang at Pohang University of Science and Technology, Professor H Lee at Korea Advanced Institute of Science and Technology and Professor H Zeng at the University of Alberta. I was responsible for SFA and AFM data collection and analysis as well as the manuscript composition. C Lim and S Kim were responsible for XPS and AFM data collection and analysis as well as the manuscript composition. Dr. H Lee, Dr. H Zeng and Dr. DS Hwang were the supervisory authors and were involved in concept formation and manuscript composition. vi Acknowledgements After more than four years of PhD study, I am proud to declare that I have achieved one of the greatest moments in my life: my student journey is going to be finished and I will move forward to the next step of my career. This thesis would not have been completed without the help and support from a lot of people, and I would like to express my sincere gratitude to all of them. First of all, with immense respect and gratitude, I would like to thank my supervisor, Prof. Hongbo Zeng, for his thoughtful insights, immeasurable guidance and support for my PhD study. It was Dr Zeng who guided me through the door into the new area regarding surface forces and colloid interfaces. I will always memorize those visionary advices that he has given to me on