Assembly and Physico-Chemical Properties of Polyelectrolyte Multilayer Films Co-Assembled with Guest Species
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Polyelectrolyte multilayer (PEM) films are typically made of two oppositely charged polyelectrolytes held together by electrostatic interactions. PEM films embedded with guest species, that is with foreign small molecules or other chemical moieties, such as surfactants, lubricants, transition metal ions or nanoparticles, have been investigated. The interaction of these various foreign species with the PEM film is of fundamental interest, influencing many properties such as strength or wettability. In one example, when assembled in the film, different types of ions or charged molecules will behave as crosslinkers and make a significant difference in film assembly and related disassembly mechanisms, compared with the more usual case of two polyelectrolytes held together by electrostatic interactions. An amphiphilic surfactant can be co-assembled to fine tune the wettability via modulation of morphology of the hydrophilic head and hydrophobic tail groups of surfactant in the film. A hydrophobic lubricant layer can improve the omniphobicity and slide off properties of a PEM. Incorporation of transition metal ions into the polyelectrolyte multilayer structure gives us a way to modulate both the ionic crosslink density as well as incorporate optical properties unique to those ions (such as color). These doped films show a difference in response to various stimuli such as pH, salt and surfactant, as well as self-healing and swelling properties. Moreover, the transition metal ion incorporated films can be reduced in situ to form particle embedded films suitable for various for optical and catalytic applications.