Movil-Cabrera, Omar A.

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    Thin film processing and the morphological and mechanical characterization of Sulfonated Poly (Styrene-Isobutylene-Styrene) (Sibs) triblock copolymers
    (2013) Movil-Cabrera, Omar A.; Padovani-Blanco, Agnes M.; College of Engineering; Acevedo Rullan, Aldo; Suarez, Oscar M.; Suleiman Rosado, David; Department of Chemical Engineering; Morell Cruz, Luis
    This work focuses on the fabrication and characterization of SIBS thin films deposited via spincoating for potential applications in microelectrochemical devices. The main goals of this project are to determine suitable parameters to fabricate uniform and continuous SIBS thin films and to perform the materials characterization with particular emphasis on the morphology as well as on the mechanical and adhesive properties of the films. The materials properties are evaluated as a function of critical parameters such as the sulfonation percent and polymer concentration in the films. The effect of hydration and temperature on the mechanical properties of the films is also considered. NafionĀ® thin films are assessed for comparative purposes. A variety of techniques are used for the materials characterization including profilometry, optical microscopy, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, differential scanning calorimetry (DSC), nanoindentation, scratch adhesion testing, and scanning electron microscopy (SEM). The results show that the film continuity and uniformity, as well as the film thickness, increases as a function of both, sulfonation percent and polymer concentration. AFM studies reveal phaseseparated morphologies with critical transitions from a short-range ordered cylindrical/lamellar morphology to a more disordered morphology (network-like structure) as the sulfonation percent increases in the films. Nanoindentation results show that both, the elastic modulus and hardness, increase with the sulfonation percent, except for the 5 wt% polymer films, where the elastic modulus decreases most likely as a result of higher solvent and/or moisture retention in the films. Conversely, the mechanical properties significantly decrease with polymer concentration regardless of the sulfonation percent of the films. A potential correlation is established between the morphology and the mechanical properties of the SIBS thin films. In general, films with a network-like structure exhibit improved mechanical properties as compared to films that exhibit non-interconnected domains. Also, SIBS thin films are more thermo-mechanically stable as compared to NafionĀ® films, even at low sulfonation percent. Scratch adhesion testing reveals that the practical adhesion for the SIBS thin films is higher as compared to the NafionĀ® films.