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<p>Bacterial biofilms are problematic in a variety of industries hence strategies for their mitigation have received significant attention. The approach described herein attempts to control bacterial adhesion using silicone-based polymers- (widely used due to their interesting properties)- via manipulation of their surface chemistry to eventually create anti-fouling surfaces. This involved study of the systematic variation of surface wettability and its effect on <em>Escherichia coli</em> (<em>E. coli</em>) adhesion to novel polymers of acrylate-modified silicone surfactant (ACR) with either hydroxyethyl methacrylate (a hydrophilic monomer), or methyl and butyl methacrylate (hydrophobic monomers). It was hypothesized that the systematic variation of ACR would produce surfaces with differing wettability, without changing other surface properties that influence cellular adhesion. Average light transmittance across the range of visible light wavelengths (400-740nm), surface roughness and Shore 00 hardness data were consistent across the ACR-HEMA copolymer series (80-90%, ~2.5 – 5 nm, and 75-95 Shore durometer points, respectively). The same consistency was observed for surface wettability (contact angles = 78-92°) despite varying HEMA content and consequently <em>Escherichia coli</em> (<em>E.coli</em>) adhesion, likely due to system saturation with silicon (as confirmed by EDX). However, wettability of the ACR-MMA-BMA polymers did vary; ≤ 20 wt% and ≥ 80 wt% ACR polymers had contact angles between 67°- 77°, while 20 < x < 80 wt% ACR polymers had increased surface wettability (contact angles 27.6°- 42.9°). <em>E. coli </em>adhesion across the set increased with increasing ACR content, a trend mirrored by the water uptake of the materials but not the contact angle data. These results indicate that <em>E. coli </em>adhesion occurs independently of wettability for these materials and although the effect of the latter on adhesion cannot be deduced, the possible correlation between bacterial adhesion and water uptake suggests that the best antifouling surfaces should not be of materials capable of imbibing significant amounts of water.</p> / Master of Applied Science (MASc)

<p>Silicones are a class of polymeric materials broadly used in numerous commercial applications, primarily due to the significant advantages they poses over their carbon-based analogues. The technology utilized to synthesize them is rather mature, and most ‘new’ synthetic strategies involve only incremental changes to the existing norm. The high level of structural control that has become the hallmark of organic synthesis and increasingly of polymer chemistry is essentially absent from silicone chemistry. The origin of this deficiency is the susceptibility of silicone polymers to redistribution (metathesis/rearrangement) under acidic and basic conditions, which will destroy any existing controlled architectures. The Piers-Rubinsztajn reaction, catalyzed by tris(pentafluorophenyl)borane (B(C₆F₅)₃), involves the direct coupling between an alkoxysilane and hydrosilane forming a new siloxane linkage, (R₃Si-OMe + H- SiR’₃ → R₃Si-O-SiR’₃ + Me-H). The reaction avoids any unwanted acidic/basic reaction conditions and has been shown previously to provide an efficient route to precise, well-defined silicones.</p> <p>Herein, the functional tolerance of the Piers-Rubinsztajn reaction is reported. It has been shown that in the presence of Lewis basic functional groups (such as – OH, -NH₂, -SH) unwanted side reactions result. However in the presence of haloalkanes and alkenes the reaction is fully tolerant, leading to the synthesis of over twenty new, well-defined functional silicones.</p> <p>The ability to utilize prepared functional silicones in common organic transformations is also reported. It has been shown that prepared halocarbon- modified silicones can readily be converted to their subsequent azido derivatives and tethered to alkyne-modified poly(oxyethyene) (PEG or PEO) of a variety of molecular weights. This led to the synthesis of over fifteen new, well-defined silicone surfactants. Structure activity relationships have also been reported for the synthesized surfactants, showing that subtle manipulations to the silicone hydrophobe can substantially alter the properties the surfactants possess. The use of thiol-ene click chemistry which involves the reaction between prepared well-defined alkene containing silicones and thiol modified poly(oxyethylene) of varying molecular weights is also reported, providing another route to well- defined silicone based surfactants.</p> <p>The use of the Piers-Rubinsztajn reaction in the synthesis of larger, well-defined silicone based macrostructures is also reported. It has been shown that through alternation between the Piers-Rubinsztajn reaction and platinum catalyzed hydrosilylation, well defined silicone dendrimers can be obtained with relative ease through a combination of both divergent and convergent growth methods.</p> <p>Finally, a new method for the preparation of both silicone elastomers and silicone foams is reported. Through use of the Piers-Rubinsztajn reaction, elastomers can be readily obtained. A detailed analysis of the many factors that may alter the overall properties of the elastomers produced including solvent volume, crosslinker concentration and type and the molecular weight of the starting hydride terminated polydimethylsiloxane (H-PDMS-H) is discussed.</p> <p>Taking advantage of the volatile hydrocarbon byproducts of the Piers-Rubinsztajn reaction, silicone foams can also be prepared using this method. A study analogous to that carried out on the silicone elastomers is also reported, showing that through subtle manipulations to the silicone foam formulations, significant changes to the materials properties can be obtained.</p> / Doctor of Science (PhD)

The adsorption of cationic and zwitterionic surfactants is studied in aqueous electrolyte solutions. A Maxwell relation is applied to Atomic Force Microscopy (AFM) data to obtain changes in surfactant adsorption as a function of the separation between two glass surfaces. In addition, self-consistent field theory (SCF) is used to calculate the adsorption profiles and interaction energies when two solid surfaces are brought into close proximity. Addition of surfactant is shown to affect the surface forces when lateral surfactant chain interactions are significant. The surfactant adsorbs and desorbs in response to over-lapping electric double-layers, with the adsorption being affected at larger solid-solid separations when the double-layer force is longer ranged. Furthermore, elimination off the surface charge or net surfactant charge eliminates adsorption with decreased solid-solid separation. The magnitude of the changes in surfactant adsorption at decreased separations is shown to scale with the chain length of the surfactant. Surfactant adsorption exceeds that required to regulate the surface charge according to the constant potential boundary condition in Poisson-Boltzmann theory. An equation of state including short-ranged (contact) tail interactions is proposed to describe both the adsorption of surfactant and the surface forces at small separations, where the double-layers overlap. Furthermore, SCF calculations show confinement-induced phase transitions when the surfactant layers on opposite surfaces merge. These phase transitions lead to further surfactant adsorption and a corresponding attractive force. / Ph. D.

The primary differences between the solventborne and waterborne epoxy printed circuit board (PCB) impregnating resins arise from the distinct physical compositions and drying characteristics of the polymer solution and the latex emulsion. The presence of residual surfactant from the waterborne epoxy emulsion poses a concern for dielectric performance and adhesive durability. Another problem involves the crystallization of insoluble solid dicyandiamide (DICY), which is significantly different in morphology than that found in solution cast resins. A two-stage drying model was employed to gain a better understanding the drying and coalescence processes. The process of surface DICY crystal formation during the drying of glass prepreg sheet was related to a threshold concentration of the curing agent in the impregnating latex resin formulation. Conditions favoring faster drying lead to the rapid formation of a coalesced skin layer of latex resin, thereby trapping the curing agent in the bulk and reducing the surface deposition of DICY by percolating water. Surfactant is believed to remain concentrated in a receding wet zone until it is driven to the surfaces of the glass fibers upon the completion of drying. The copper foil/laminate interface was evaluated by a 90° peel test as part of two different studies: an analysis of the viscoelastic response of the interface during peel and a study of the thermal durability of the copper/laminate interfacial peel strength. The surfactant acted as a plasticizer to toughen the fiber/matrix interphase, resulting in larger observed peel strengths in the latex resin impregnated materials relative to the solventborne system. Surfactant segregated to the fiber surface during coalescence to form a plasticized fiber/matrix interphase; surfactant migrated into the bulk during postcure to yield a more homogeneously plasticized epoxy matrix. Dielectric measurements of neat resin and laminate materials revealed that the dielectric constants of the model resin-impregnated laminates met the performance criteria for PCB substrates of their class, regardless of surfactant content. Overall, the adhesive performance, adhesive durability, and dielectric properties of PCB systems fabricated with model latex epoxy resin, containing native surfactant (5 wt %), met or exceeded the performance of an equivalent solventborne resin impregnated system. / Ph. D.

Advanced analytical techniques were utilized to investigate the intermolecular forces in several nanostructured materials. Techniques including, but not limited to, isothermal titration calorimetry (ITC), variable temperature Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) thermal curves were used to study the fundamental interactions present in various nanomaterials, and to further probe the influence of these interactions on the overall behavior of the material. The areas of focus included self-assembly of surfactant micelles, polycation complexation of DNA, and temperature-dependent hydrogen bonding in polymeric systems. ITC was successfully used to determine the low critical micelle concentration (CMC) for a novel gemini surfactant with limited water solubility. CMCs were measured at decreasing methanol molar fractions (xMeOH) in water and the resulting linear relationship between CMC and methanol concentration was used to mathematically extrapolate to a predicted CMC at xMeOH = 0. Using this technique, the CMC value for the novel gemini surfactant was predicted to be 0.037 ± 0.004 mM. This extrapolation technique was also validated with surfactant standards. ITC was also used to investigate the binding thermodynamics of polyplex formation with polycations and DNA. The imidazolium-containing and trehalose-based polycations were both found to have endothermic, entropically driven binding with DNA, while the adenine-containing polycation exhibited exothermic DNA binding. In addition, ITC was also used to confirm the stoichiometric binding ratio of linear polyethylenimine and DNA polyplexes as determined by a novel NMR method. Dynamic light scattering (DLS) and zeta potential measurements were also performed to determine the size and surface charge of polyplexes. Circular dichroism (CD) and FTIR spectroscopies provided information regarding the structural changes that may occur in the DNA upon complexation with polymers. UV-Vis thermal curves indicated that polyplexes exhibit a greater thermal stability than DNA by itself. Variable temperature FTIR spectroscopy was used to quantitatively compare the hydrogen bonding behavior of multi-walled carbon nanotube (MWCNT)-polyurethane composites. Spectra were collected from 35 to 185 deg C for samples containing various weight percent loadings of MWCNTs with different hydrogen bonding surface functionalities. Peak fitting analysis was performed in the carbonyl-stretching region for each sample, and the hydrogen-bonding index (Rindex) was reported. Rindex values were used to quantitatively compare all of the composite samples in regards to temperature effects, weight percent loadings of MWCNTs, and the different functionalizations. In general, higher weight percent loadings of the MWCNTs resulted in greater Rindex values and increased hydrogen bond dissociation temperatures. In addition, at 5 and 10 wt% loadings the initial Rindex values displayed a trend that tracked well with the increasing hydrogen bonding capacity of the various surface functionalities. / Ph. D.