Distribution of quaternary ammonium salt encapsulated polyoxometalates in polyurethane films

Abstract The distribution behavior of amphiphilic quaternary ammonium salt (QAS) encapsulated nickel substituted polyoxometalates (Ni-POMs) in hydrophilic and hydrophobic polyurethane films for potential coating additive applications was investigated. The relative lengths of the alkyl and ethoxy tail moieties of QAS exhibited significant effects on additive distribution behavior within polyurethane. Nonpolar-polar interactions between the QAS(Ni-POM) additive and polyurethane matrix determined dispersion and segregation of the additives. Incorporation of QAS(Ni-POM) in polyurethane resulted in the formation of circular surface domains, the diameters of which were dependent on QAS composition, loading concentration, and solvent evaporation rate. XPS depth profiling analysis indicated that QAS(Ni-POM)s surface segregated in both hydrophilic and hydrophobic polyurethanes. Reduced antimicrobial activity of the QAS(Ni-POM) coatings relative to QAS coatings confirmed that QAS remained coordinated to POM during film preparation. Alkyl tail length affected the hydrophilic character of QAS(Ni-POM), while ethoxy tail length modulated effective molecular radius, both of which are facile means to control the dispersion and phase separation of encapsulated POMs in polyurethane coatings.