Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Chemistry

Language

English (en)

Date of Award

January 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Karen Wooley

Abstract

The overall emphasis of this dissertation research included the development of novel amphiphilic anti-fouling coatings having complex surface topography and compositional heterogeneity and a fundamental investigation of their properties. These films were cultivated as non-fluorinated or non-fluorinated/non-PEGylated analogs to the hyperbranched fluoropolymer-poly(ethylene glycol): HBFP-PEG) film system. The coating compositions consisted of the mixing and crosslinking of either two disparate polymers or a complex amphiphilic block copolymer with crosslinking agents. A variety of crosslinking methods was analyzed, including vulcanization and UV-promoted thiol-ene reactions. The coatings were analyzed using a variety of advanced methods, including thermomechanical techniques, tensile testing and surface analysis. A combinatorial series of UV-promoted, thiol-ene generated amphiphilic films was prepared by the crosslinking of varying wt% of 4-armed poly(ethylene glycol): PEG) tetrathiol and equivalents of pentaerythritol tetrakis(3-mercaptopropionate): PETMP) with alkene-modified Boltorn polyesters. The Boltorn-alkene components were prepared through the esterification between commercially available Boltorn H30TM and 3-butenoic acid. The thermomechanical attributes of the films were analyzed, showing an increase in Tg with an increase in PEG wt%, regardless of PETMP concentration. The films were then studied for their bulk mechanical properties in both dry and wet state. The nanoscopic surface features were probed using atomic force microscopy and contact angle analysis. Additionally, a series of coatings were prepared at a low PETMP concentration with varying PEG wt%: 0-35 wt%), where they were tested for anti-biofouling character and fouling release ability against Ulva marine algae. The films have a vastly decreased spore settlement and growth when compared to commercial PDMS coatings. A non-fluorinated, non-PEGylated analog of the HBFP-PEG system was synthesized using RAFT copolymerization. It was hypothesized that the non-ionic polar polymer, poly(N-vinylpyrrolidinone): PNVP), would work as a more durable replacement for the hydrophilic PEG of the original system and that the hydrophobic polymer polyisoprene: PIp) could be used as a low surface energy, potentially multi-crosslinkable analog of HBFP. Vulcanization crosslinking methods were employed during polymer phase segregation, driven by differences in composition and macromolecular topology. The new design differs not only in the chemical compositions: PIp for HBFP and PNVP for PEG), but also in the macromolecular architecture. The complex films were analyzed using a variety of advanced surface analysis, including XPS, IRIR imaging, and XPS. A similar block copolymer system was investigated, PEO-b-PIp, as an additional analog to HBFP-PEG. Two RAFT-capable PEO macro-CTAs, 2 and 5 kDa, were prepared and used for the polymerization of isoprene which yielded well-defined block copolymers of varied lengths and compositions. Mathematical deconvolution of the GPC chromatograms allowed for the estimation of the blocking efficiency, about 50% for the 5 kDa PEO macro-CTA and 64% for the 2 kDa CTA. Self assembly of the block copolymers in both water and decane was investigated and the resulting regular and inverse assemblies, respectively, were analyzed with DLS, AFM, and TEM to ascertain their dimensions and properties. Assembly of PEO-b-PIp block copolymers in aqueous solution resulted in well-defined micelles of varying sizes while the assembly in hydrophobic, organic solvent resulted in the formation of different morphologies including large aggregates and well-defined cylindrical and spherical structures. Additional investigation into the potential anti-fouling ability was performed using fluorescently-tagged biomolecule adsorption assays. During the studies of these analogs, several discoveries were made with the original HBFP-PEG system on which the dissertation author is listed as co-author. Since the work was performed in conjunction with the dissertation author and is pertinent to the dissertation, the work is included in the Appendices. Nanocompositing materials, specifically carbon nanotubes and nanoscopic silica, were either physically mixed or engineered to be phase-specific for either the HBFP domain or the PEG domain. The nanocomposited HBFP-PEG materials were then subjected to a variety of mechanical tests in order to see how the compositing agents effected modulus in either dry or wet environments. Additional advanced investigations into the unique mechanical properties of HBFP-PEG were performed using solid-state NMR. At varying wt% PEG, the wetted film acts as either a structurally-reinforced material: sub-45 wt%) or as a mechanically-weakened hydrogel: >55 wt%). The mechanism of the structural reinforcing was probed using a variety of advanced solid state NMR techniques, providing information into the unique mechanical properties of the HBFP-PEG material.

DOI

https://doi.org/10.7936/K7QF8QWM

Comments

Permanent URL: http://dx.doi.org/10.7936/K7QF8QWM

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