Study On The Phase Separation Morphology And Deformation Recovery Behavior Of Block Copolymers

Block copolymers can self-assemble and lead into a variety of extremely regular morphologies during the microphase separation. As these ordered morphologies can be considered as templates for the fabrication of corresponding nano-structures, scientist have focused on the tuning of these architectures in recent years. And the relationship between these ordered structures and such properties as mechanical behavior has a crucial impact on future nano-processing techniques. In this paper, the effect of evaporation speed and post solvent annealing of cyclohexane as well as the thickness of films on the microdomain patterns mainly formed by poly(styrene-ethylene/butylene-styrene) (SEBS) triblock copolymers was studied using Tapping-Mode Atomic Force Microscope (TM-AFM), including the morphology changes of blends of SEBS and poly(styrene-butadiene-styrene) (SBS) triblock copolymers in xylene's annealing. Moreover, the influence of morphologies on the deformation recovery behavior of SEBS under annealing conditions was also investigated by AFM. And the results are as follows:Firstly, the morphology transition of SEBS film changed from disordered, long-range continuous structure to mixed structure with both sphere and cylinder as we slowed the evaporation speed of cyclohexane. The morphology transition of SEBS film upon annealing in cyclohexane was tracked using AFM ex-situ observation strategy for the SEBS film as-cast from solution in xylene, which appeared that the SEBS film was in the process of the mutual transition of sphere and cylinder morphology in cyclohexane's annealing, but obviously, the orientation degree of cylinder microdomain had increased at last.Secondly, the thickness of film has an important influence on the morphology in the process of casting. The morphology changed from unconspicuous net, ununiform distributed sphere, long-range continuity to disorder morphology when the thickness varied from 11, 13, 15 to 30 and 40nm..Thirdly, the macrophase separation was observed in the as-cast films of blends of SEBS and poly(styrene-butadiene-styrene) (SBS) triblock copolymers, but it disappeared in xylene's annealing. Finally, in the residual deformation recovery experiment after scratching a hole on the surface, a linear relationship was found between the recovery percentage and the logarithm of relaxation time for all samples. Basically, the speed of recovery quickened as the annealing temperature increased. At the temperature of 323 and 333 Kelvin, the recovery speed of SEBS film with net morphology was the fastest, and the second faster was cylinder, followed by disorder morphology; while at 343 Kelvin, their recovery speed had no significant difference, as the morphology transition happened from cylinder and net to disorder. Therefore, it's a crucial factor to the deformation recovery behavior that whether the polystyrene (PS) phase was continuous or not. In a word, the effect of phase separation morphology on the deformation recovery behavior was not so distinct as annealing temperature did.