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Eric Williams - Water Sorption, Swelling and Hydrogen Bonding Properties of Model Thermoplastic Corrosion Control Coatings via Attenuated Total Reflectance FTIR at the Substrate Interface

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Eric Williams - Water Sorption, Swelling and Hydrogen Bonding Properties of Model Thermoplastic Corrosion Control Coatings via Attenuated Total Reflectance FTIR at the Substrate Interface

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Eric B. Williams

Research Associate

The University of Southern Mississippi

Phone: 601-266-5683

Co-Authors: James W. Rawlins

 

Abstract

    Diffusion of small molecules and salts through the polymer matrix of a coating system used for corrosion control has often been attributed to and correlated with the corrosion rate of the underlying asset.  Quantifying the diffusion-related properties of small molecules into, through, and beneath the polymer matrix with respect to swelling and hydrogen bonding is expected to result in a better understanding of the material design and engineering requirements for a responsive material system that can act to inhibit free diffusion of solvated ions and functions to protect the underlying asset through confinement of water and salts within the polymer film.  If we understand how the polymer matrix material responds to environmental factors like water and salts, then direct management of water and salt transport by the polymer matrix is thought to be possible by incorporating molecular, micro, and/or meso functionalities specific for management of coating physical properties necessary for corrosion control.
     In this work we used a model linear poly hydroxyl ether thermoplastic polymer and report on the sorption rate of water with increasing concentrations of salt using ATR-FTIR real time spectroscopy to observe and quantify the swelling, water hydrogen bonding, and aqueous saturation at the polymer-substrate interface.  By intentional exposure of a salt solution on the air-interface of a coating, we can characterize and measure the differential in hydrogen bonding of water within the coating material at the substrate interface.  Within these characterization results we observed and were able to quantify substrate-side swelling of the polymer film relative to the total water saturation of the coating in real time.  Using ATR-FTIR, we found that the polymer matrix sorbed water and swelled in the Z-axis with the greatest swelling inversely proportional to salt concentration within the polymer matrix.  Furthermore, we observed an increase in unbound water within the polymer matrix with decreasing salt concentrations.  We believe these two findings are related and dependent in regards to molecular-level water-polymer interactions necessary to affect inhibitor release rates within a coating system and shift when and how corrosion initiation and corrosion propagation occurs.  We hypothesize that there are portions of the polymer matrix directly based upon the individual molecular building blocks that have a differential in water affinity based on water solubility parameters.  These in turn allow water to preferentially organize within the matrix and thereby diminish permeation rates through transient bonding with the polymer phase.  Using a model thermoplastic polymer system that swells in relation to the organization of water in a dependent manner specific to water affinity, we can better understand where, and to what extent, these functional groups should be limited within a polymer coating to tailor the water partition within a coating to manage the diffusion of solvated ions to the coating substrate.  Additionally, ion entrapment was observed when salt is present the polymer regions that cannot swell in the presence of water which is likely exhibiting greater confinement as a response from the ionic/dielectric and chemical potential dynamics driven by salt participation in the polymer, which has been shown to manage water transport.

 

Biography

Eric Williams s currently a post-doctoral fellow with the Thames-Rawlins Research Group at The University of Southern Mississippi.  He has 17 publications, four patents (three pending), over 40 presentations, and 435 citations to his credit.  His research experience spans enzyme mediated catalysis in polymer thin films, nanocomposites, high temperature composites, polymer degradation, and polymer material characterization. His current research is focused on understanding structure-property relationships of coatings with particular emphasis on studying small molecule penetrants and diffusion related effects on anticorrosive coatings.

 

 

 

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