(522g) Thin Film Processing and Characterization of Sulfonated Poly(Styrene-Isobutylene-Styrene) Triblock Copolymers

Thin films of sulfonated block copolymers are of particular interest for applications in microelectrochemical devices such as sensors, biosensors, fuel cells, and actuators. This study focuses on the fabrication and materials characterization of sulfonated poly(styrene-isobutylene-styrene) (S-SIBS) triblock copolymer films. More specifically, the morphological and nanomechanical properties of the films were targeted such as to understand their integration capability. For these studies, S-SIBS thin films were deposited onto silicon wafers via spin-coating and critical parameters such as sulfonation percent and polymer concentration were evaluated. The effects of a thermal annealing treatment on film morphology were also investigated. A variety of techniques were used for the materials characterization including profilometry, atomic force microscopy (AFM), and nanoindentation. Profilometry results showed that at high polymer concentrations, the films were approximately 10 times thicker as compared to the films fabricated at low polymer concentration. The latter had thickness values on the order of < 1µm. The film thickness also increased with the sulfonation percent in the film. AFM results revealed a morphological transition from spherical domains to a network-like structure as the sulfonation percent increases from 0% to 45%. In addition, the polystyrene (PS) domain size also increases as a function of the sulfonation percent. Significant effects on the phase-separated morphology were also observed as a result of the thermal annealing treatment, but only in the films fabricated from membranes with a T_g lower than the annealing temperature. Nanoindentation results indicate that both, the elastic modulus and hardness, increase with the sulfonation percent in the film and the differences observed correlate with changes in morphology.