Effect of Processing Variables on the Structure and Properties of Plasma Polymerized Films on Metal Substrates

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Project Summary Proposal Number: CTS-9407809 P.I.: Boerio Institution: University of Cincinnati Plasma polymerization is a process in which active species such as ions and radicals are formed in a low pressure gas or plasma of a "monomer" by collisions between free electrons and monomer molecules when an electric field is applied to the gas. The active species react with themselves or with monomers to form polymer coatings on the surfaces of solids that are exposed to the plasma. Plasma polymerization is an extremely attractive process for pretreatment of investigations of metals since it enables materials synthesis and processing to be combined into one step. Many investigations of plasma polymerization have been reported but most have focused on only one aspect, such as the effect of processing variables on the rate of film formation. In this research, the University of Cincinnati is collaborating with Ford Motor Co. and Goodyear Tire and Rubber Co. to determine relationships between the processing variables that are used to deposit plasma polymerized films on metal substrates, the molecular structure of the films, especially the surface and interfacial structures, and the performance of the films as primers for rubber-to-metal and spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), reflection-absorption infrared spectroscopy (RAIR), ellipsometry, surface-enhanced Raman scattering (SERS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) will be used to determine the effect of processing variables such as discharge power and frequency, monomer, flow rate, pressure, and substrate surface chemistry on the molecular structure and morphology of the films. Electrochemical impedance spectroscopy (EIS), fracture mechanics tests, and industrial test methods will be used to determine performance characteristics of the films such as the corrosion protection they impart to metal substrates, the interfacial fracture energy of films deposited on metal substrates, and the properties of the films as primers for rubber-to-metal and structural adhesive bonding. Surface analysis will be used to examine the failure surfaces of specimens after fracture mechanics and adhesive bonding tests to determine the failure mechanisms. The results obtained will be used to develop relationships between the processing variables used to deposit the films, their molecular structure, and their properties and will represent a significant enhancement to the knowledge base in the important, rapidly expanding field of thin polymer films. Collaboration with Ford will mostly involve structural adhesive bonding of aluminum and surface analysis. Collaboration with Goodyear will involve rubber-to-metal bonding and surface analysis.