Robust Gyroid Morphology in Triblock Terpolymer Films During Solvent Vapor Annealing

Controlled solvent annealing is known to effectively generate ordered block copolymer films. In addition, films of desired morphology (spheres, cylinders, gyroids, or lamellae) can be produced by annealing films using solvent mixtures of tuned selectivity. While this has been investigated in detail for diblock copolymers, the effect of selective solvent annealing has not yet been studied for the next more complicated family of linear block copolymers, triblock terpolymers. We present the results of in situ GISAXS during solvent annealing of gyroid-forming polyisoprene-b-polystyrene-b-poly(ethylene oxide) triblock terpolymer films. The selectivity was adjusted by using mixed vapor ratios of tetrahydrofuran and methanol. In contrast to diblock copolymers, we found the gyroid morphology irrespective of the solvent vapor ratios used for annealing of the terpolymer film. Furthermore, we show that the robust nature of the gyroid morphology allows for generating films with long-range order.