Nonlinear Vibrational Probes of Structure at Charged Polymer-Aqueous Interfaces

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Polymers are used to produce many of the objects we encounter in our daily life, from car bumpers to shampoo bottles to dental fillings. While the bulk properties of these materials are tuned to make them stiff or pliable, transparent or opaque, an equal amount of attention goes into tailoring their surface properties to best interact with their intended surroundings. For example, materials such as acrylic are widely used in creating medical implants as they are strong and lightweight, but their surfaces are not naturally biocompatible. Exposing the polymer surface to an ionized gas called a plasma is one method by which scientists improve the interaction between acrylic and proteins in the body. But the nature of the polymer surface is not the sole contributor to mediating environmental interactions: water molecules in contact with any material have markedly different properties from bulk water. As a result, the way in which water surrounds proteins is vastly different a few nanometers from the polymer surface, tens to hundreds of nanometers away, and in the bulk water phase. Understanding how the polymer surface interacts with water is therefore critical to developing a holistic view of surface structure and adhesion processes. In the proposed program, we use high power visible and infrared lasers to probe microscopic changes that occur on the polymer surface in response to high-voltage plasma treatment. We then follow the change in how water molecules interact with the surface before and after treatment to better understand how the wetting characteristics of the polymer have been altered. Later projects will introduce biological molecules such as amino acids, peptides and proteins to characterize their adsorbed structure, and solidify our understanding of these complex but fundamental molecular interactions. The field continues to be hindered by generalizations such as the expectation for globular proteins to denature on hydrophobic surfaces. The past five decades have provided many examples where this is not true, pointing to the need for a detailed molecular-level understanding of surface interactions, starting with the substrate and the solvent. Research in this area is important to biomedical engineers as it provides guidance for the next generation of medical implant coatings and surface treatments, or ideas for improving existing ones. Polymer surface charge modification is important in textile processing, as plasma-treated fibres have increased adhesion to dyes, dramatically reducing or eliminating the need for solvents that are harmful for workers and the environment. Studying charged polymer surfaces also leads to improved understanding of how lightweight insulators withstand weathering for reliable overhead power distribution to Canadian towns and cities. Along the way, our work in this area provides many training opportunities for the next generation of scientists and engineers.