Study of Hydrophilic Zones to Improve the Performance of Organic Coatings. Heterogeneity of Polymer Film: Characterization and Protective Properties

摘要

Characterization of heterogeneous phases in polymers and hydrophilic regions in coatings have been the subject of AFOSR funded research project. Although hydrophilic regions occupy only a small fraction of the coating film volume. the hydrophilic regions control the corrosion protection performance of a polymer coating. At present the progress in the characterization of hydrophilic regions in coatings is very limited because of the lack of suitable analytical technique that can provide nanoscale lateral information. We mapped mechanical and chemical heterogeneities in model polymer coating compounds and characterized degradation susceptible regions in commercial coatings at nanoscale level. Nanoindentation procedure in combination with TMAFM was used to identify soft and hard regions in a heterogeneous model coating compound. To map chemically heterogeneous regions in model systems. we developed AFM/chemical modification approach. An effort was made to relate the microstructure of polymer coating film to the changes that occur to film upon environmental exposure and relate the changes to the chemistry of degraded compound. The material leached out from the coating during immersion was characterized. The leached material was mostly unreacted starting monomers and oligomers. They probably represent the degradation-susceptible regions (hydrophilic regions) of coating film. With the use of an atomic force microscope (AFM). which provides nanometer spatial resolution and angstrom depth resolution, we recently observed the progression of pathway formation in polyester and acrylic-polyurethane coatings, common protective materials for industrial, automobile, and aerospace applications. FTIR results in combination with AFM results (pit formation) support the observation that the extent of degradation of polyurethane coating film is much larger for samples exposed to UV at high relative humidities compared to no UV and high relative humidity.