The global market for fluoropolymers, including polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), is growing rapidly due to their copious applications in the construction, automotive, medical, chemical, and electrical industries. Fluoropolymers owe their popularity partly to their excellent chemical and thermal stability and useful mechanical, piezoelectric, and ferroelectric properties. They are made into films or coatings that are used for corrosion protection or surface property enhancement. Electrophoretic deposition (EPD) has generated increasing interest in manufacturing advanced films for various applications due to its low cost, versatility, simple apparatus, and good film quality compared with other deposition techniques like dip coating, spin coating, electrospinning, or spay coating. Moreover, EPD facilitates uniform deposition on the substrates of complex shapes at a high deposition rate.
The aim of this research is to develop novel biomimetic strategies for fabricating polymer films and their composite films with multifunctional particles through EPD. This method involves the electrophoresis of charged particles in a stable colloidal suspension towards an electrode, forming deposition. Fluoropolymers, however, are electrically neutral and chemically inert, and their EPD presents difficulties. Therefore, successful EPD depends on understanding how to modify the surface of polymer particles using advanced biosurfactants to impart charge and form a well dispersed, stable colloidal suspension.
One strategy is to leverage the unique dispersing power of bile acids and salts as biosurfactants for EPD of PTFE and PVDF films and composite films. When doing so, it was found that the amphiphilic structure of bile salts such as sodium deoxycholate (DChNa) facilitated adsorption on the chemically inert, hydrophobic surfaces of PTFE, diamond, and carbon dots. In this strategy, DChNa acted as a charging, dispersing, film-forming agent for the co-deposition of PTFE composite films from an aqueous suspension. Water insoluble bile acids (BAs) were found to be biosurfactants for the EPD of PTFE and PVDF from organic solvents, in which lithocholic acid (LCA) was used as a co-dispersant for the fabrication of composite PTFE-diamond coatings and PTFE coatings provided corrosion protection for stainless steel in 3% NaCl solutions. The dispersing performance of four other bile acids, chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), ursodeoxycholic acid (UDCA), and cholic acid (ChA), was analyzed and compared with LCA on the deposition performance of PVDF. It was found that the PVDF deposition yield obtained using different BAs increased in the order of LCA<CDCA<DCA<UDCA<ChA. This was attributed to the difference in number, position, and orientation of OH groups in the structures of the BAs.
Another biomimetic strategy for the EPD of polymers and composites was inspired by the strong adsorption of mussel protein on rock surfaces in sea water. Catecholate-type molecules, caffeic acid (CA) and catechol violet (CV), were found to be biosurfactants for dispersing, charging, and depositing PVDF films and composites. Analyses of the deposition yield data, the chemical structure of the CA and CV, and the microstructure and composition of the films suggested that the aromatic rings on the CA and CV had hydrophobic interactions with the PVDF particles and that the phenolic groups formed bidentate chelating or bridging bonding to inorganic particle surfaces. The study demonstrated the feasibility of co-depositing PVDF with nanoparticles of TiO2, MnO2, and NiFe2O4. CA was also used for preparing PVDF-HFP particles and as a co-dispersant for the co-deposition of PVDF-HFP with NiFe2O4 and CuFe2O4 nanoparticles in order to make composite films that combine the ferrimagnetic properties of spinel ferrites with the multifunctional properties of ferroelectric polymers. / Dissertation / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/28077 |
| Date | January 2022 |
| Creators | Zhao, Qinfu |
| Contributors | Zhitomirsky, Igor, Veldhuis, Stephen, Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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