Understanding antifouling mechanisms of bio-inspired functional coatings and developing antifouling surfaces based on mussel-inspired wet adhesive chemistry
Creators: Li, Sijia
Publisher: name: University of Alberta Library
Year: 2024

<p>Bio-inspired antifouling materials have been widely studied in recent years in a variety of engineering fields, such as biomedical devices, marine industry, oil/water separation, and water treatment. However, studies on the corresponding intermolecular interactions between the bio-inspired antifouling materials and various contaminants including organic, inorganic foulants and biofoulants are still incomplete, significantly limiting the related fundamental research and practical applications. In this thesis, three original research works regarding the molecular design and engineering of bio-inspired antifouling materials are presented, and the surface interaction mechanisms between bio-inspired antifouling materials and mussel-inspired chemistry, proteins, silica, humic acid, and oil droplets are elucidated with the assistance of nanomechanical techniques based on atomic force microscope (AFM). <br>
Lubricant-infused slippery surfaces have recently emerged as promising antifouling coatings, showing potential against proteins, cells, and marine mussels. However, a comprehensive understanding of the molecular binding behaviors and interaction strength of foulants to these surfaces is lacking.  In the first work, mussel-inspired chemistry based on catechol-containing chemicals including 3,4-dihydroxyphenylalanine (DOPA) and polydopamine (PDA) was employed to investigate the antifouling performance and repellence mechanisms of fluorinated-based slippery surface, and the correlated interaction mechanisms were probed using AFM. Intermolecular force measurements and deposition experiments between PDA and the surface revealed the ability of lubricant film to inhibit the contact of PDA particles with the substrate. Further analysis using single-molecule force spectroscopy (SM-AFM) highlighted that the infused lubricant layer could remarkably influence the dissociation forces and weaken the binding strength between DOPA and underneath per-fluorinated monolayer surface, offering deeper insights into the molecular binding behaviors that are essential for developing new antifouling materials.<br>
Membrane fouling significantly impairs the efficiency and quality of contaminant removal in wastewater treatment. Understanding the molecular interactions between foulants and membranes, which drive foulant attachment and growth, is crucial for developing effective antifouling strategies. In the second work, typical contaminants that existed in water filtration systems including silica particles, bovine serum albumin (BSA), and humic acid (HA) were selected for the direct force measurements on polyvinylidene fluoride (PVDF) membranes with or without the modification of PDA or poly(sulfobetaine methacrylate) (PSBMA) employing an AFM. The interaction mechanisms driving adsorption and removal of various foulants on membranes with different wettability and surface chemistry were quantitatively analyzed using extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Adhesion energy from retraction curves indicated the release and regeneration ability of membranes. PDA-functionalized membranes exhibited good antifouling performance against silica but were less effective against organic foulants due to the influence of many intermolecular forces such as hydrophobic attraction, π-interactions, and hydrogen bonding. PSBMA-modified membranes showed excellent fouling resistance and self-cleaning capabilities, driven by dominant repulsive electric double layer (EDL) and hydration forces. <br>
Developing novel membrane materials for oil-in-water (O/W) emulsion separation is of both fundamental and practical significance, but challenging, due to the serious membrane fouling issues. In the third work, a conductive antifouling coating formed by a conductive polymer blend of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) and PSBMA was prepared on PVDF membrane. Electrochemical atomic force microscopy (EC-AFM) was employed to simultaneously probe the interfacial interaction mechanisms of different membranes with oil droplets at the nanoscale, which demonstrated that the conductive membranes possessed adjustable surface charge properties with the modulation of the electrochemical potentials, resulting in tunable EDL interaction to achieve adaptive antifouling performance in response to the emulsions. Filtration measurements demonstrated that adjusting the surface charge properties of the membranes could enhance antifouling performance, leading to high oil removal efficiency (99.9%) and improved membrane reusability (89%) when -0.4 voltages were applied.<br>
This thesis work provides fundamental understandings of fouling resistance mechanisms of diverse bio-inspired materials at the molecular level and expands the application of marine mussels-derived interactions in the development of antifouling surfaces, which offers useful implications on developing novel antifouling strategies by manipulating interfacial interactions for various engineering applications such as oil production, water treatment and other industrial processes.</p>