Polymer thin films are widely utilized as industrial coatings in fields ranging from photovoltaics to organic LEDs. Polylactic acid (PLA) and polystyrene (PS) are two of the most widely used thin film polymers, and PLA/PS composite thin films are currently being investigated for use in tissue scaffolding. Little is known, however, about the interfacial diffusion, crystal formation, and roughness in these PLA/PS thin films; all three of these properties are important to the surface performance of confined polymers in thin films. In this study, various PLA, PS and deuterated styrene methyl methacrylate (dSMMA) blends were examined as confined thin films on different substrates. The first part of this study used atomic force microscopy (AFM) and ellipsometry to determine the impact of polymer chain length on crystal formation. AFM on the single-layer thin films shows that larger molecular weight PS additives significantly increased both crystal size and roughness in the annealed samples. The second part of this study aimed to determine the impact of different substrates on crystallinity, via the creation of bilayer thin films (PLA on PS and PS on PLA) using dSMMA as a potential compatibilizer. AFM on the bilayer samples showed that the roughness when the top layer was PS was 31.97% less than the roughness when PLA was the top layer; in addition, the roughness of the PS on PLA/dSMMA bilayers was significantly lower than that of any single layer sample, indicating that the bilayers offer smoother surfaces. SIMS analysis that showed that for the PS/dSMMA on PLA bilayers, dSMMA diffused into the interface, and the enhanced compatibility did not compromise the roughness or crystallinity of the composite thin films; we can observe that with increasing dSMMA concentration, the thickness of the interfacial dSMMA layer was broadened. This indicates that most of the dSMMA present diffused to the interface rather than settling in either layer, and in turn proves that dSMMA can act as an interfacial compatibilizer between PLA and PS. The study as a whole shows that both the roughness and crystallinity of the composite thin films are dependent on the substrate; the PS on PLA bilayer thin films, for which PLA was the substrate, offer the least roughness, and are stable with a dSMMA compatibilizer, which is a promising sign for future use in the biomedical and electronic fields.<br/>

Studying the crystal formation and interdiffusion mechanisms of polylactic acid thin films

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.