Browsing by Author "Orlando J. Rojas, Committee Chair"

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    Adsorption of Amphoteric and Nonionic Polymers on Model Thin Films
    (2008-08-19) Song, Junlong; Kirill Efimenko, Committee Member; Dimitris S. Argyropoulos, Committee Member; Martin A. Hubbe, Committee Member; Orlando J. Rojas, Committee Chair
    Understanding the adsorption behaviors of polymers from solution is critical in applications such as fiber processing, specifically in the development of fiber bonding and lubrication. Therefore, in situ and real time Quartz Crystal Microbalance and Surface Plasmon Resonance were employed to monitor the adsorption of hydrosoluble polymers (including amphoteric and nonionic macromolecules) on ultrathin films of cellulose, polypropylene, polyethylene, nylon and polyethylene terephthalate (typical paper and textile materials). The extent of adsorption of amphoteric polymers on cellulose (and also on silica) depended on the charge density of the substrate and pH of the medium. More importantly, the adsorbed amount exceeded that found in the case of simple polyelectrolytes. We hypothesized that this extensive adsorption is the result of a polarization effect produced by the charged substrate, which also determined the characteristics (thickness and viscoelastivcity) of the adsorbed layers as well as bonding abilities. Surface active polymers including diblock polyalkylene glycols and triblock polymers (based on ethylene- and propylene- oxide) as well as silicone surfactants were used to study the formation of boundary layers that are relevant in fiber lubrication. Adsorption isotherms for the nonionic polymers followed a Langmuirian behavior in which the hydrophobic effect was a major driving mechanism. The molecular mass of the polymer influenced markedly adsorption and, compared to typical hydrocarbon surfactants, silicone-based surfactants showed a higher surface activity and affinity with the tested hydrophobic surfaces. Lateral force microscopy and molecular dynamics simulation were used to illustrate boundary lubrication. It was concluded that surface-active molecules form robust self assembled (lubricant) layers that withstand high shear forces and are able to control friction and abrasion due to the unique molecular structures they form at the interface. Overall, it is anticipated that this thesis will contribute to the elucidation of the relationship between the structure and chemical nature of the adsorbing polymers and their respective interfacial behaviors.