The goal of this project is to employ non‐toxic, electrically neutral polymer zwitterions with varying dipole moment directions as interfacial skin layers for adjusting the work function of metal surfaces in order to resist/inhibit corrosion. Because the polymers exhibit dipole moment control, their contact with metals enables tuning of the metal work function to higher or lower values. The polymer zwitterions to be studied will be prepared with methacrylate backbones, for ease of synthesis and consistency of the backbone composition. Within this scoping project, the project team will study the behavior of electroplated zinc nickel (ZiNi) on steel coupons as a benchmark. These systems are referred to as sacrificial anodes as they essentially oxidize before the underlying substrate does. The hypothesis is that one can employ work function‐modifying polymer zwitterions to modulate the electrochemical series of elements in order to thermodynamically retard the corrosion process. The project team will characterize the metal and polymer‐metal interfaces with ultraviolet photoelectron spectroscopy, electrical/impedance measurements, density functional theory calculations, surface morphology studies, and neutral salt spray tests to verify the durability and service life of the modified substrates. This collaboration between the Naval Air Warfare Center Weapons Division and the University of Massachusetts, Amherst will enable the production of corrosion‐resistant components as candidates for use in ships hulls, jetties, offshore oil and gas drilling rigs, and floating docks and piers.
Polymer zwitterions for this project will be synthesized by the Emrick group at the University of Massachusetts, Amherst. Well known for their low toxicity and environmentally benign properties, these polymer zwitterions are additionally advantageous for being pH insensitive, electronically neutral, and structurally well‐defined. Crucial functional attributes of polymer zwitterions include: 1) they can be solution processed using solvents orthogonal to those used for subsequent organic layer deposition, and 2) their large dipole moment enables control over the work function (WF) of a broad range of useful metals. The approach is to modify ZiNi sacrificial coupons and modulate their oxidation properties by spin coating a thin layer of polymer zwitterions onto their surface. By judiciously choosing zwitterions with varying dipole moment strengths/directions, one can effectively modulate the electrochemical series with the ZiNi coupon substrate and control the rate of corrosion. The synthesis and processing of the polymer is environmentally benign – the lack of metal catalysts and amenability to environmentally benign solvents aligns well with the Department of Defense environmental program goals.
This project would be the first of its kind to examine polymer zwitterions for WF control in the context of anticorrosion studies, with the recognition that prior work by the investigators in using polymer zwitterions for WF control is hypothesized to be specifically useful to address metal corrosion. This project could potentially have the largest impact in corrosion control where electroplating or high temperature annealing of metals may not be required. The simple concept of electronic structure of metals and polymers is all that is needed to effectively modulate the electrochemical series of modified alloys to reduce the corrosion process.