Kinetically Trapped Block Copolymer Nano‐Objects with Cylinder to Sphere Shape Transition Properties

Here, the cylinder to sphere transition property is reported in kinetically trapped block copolymer (BCP) nano-objects made from polystyrene-block-poly(N-isopropylacrylamide) (PS-b-PNIPAM) in ethanol. The PS-b-PNIPAM BCPs are found to self-assemble into hexagonally packed cylindrical morphology in bulk. When dispersing the bulk microphase-separated BCP materials in selective solvent, nanocylinders stabilized by kinetically trapped PS cores were obtained. However, when the kinetic barrier is removed by external energy input, a morphology transition from cylinder to sphere occurred. The transition procedure could be accelerated by applying higher external energy, which could be realized by using higher temperatures as well as treating with ultrasonic. Additionally, lowering the kinetic barrier by using polymers with a shorter PS block also accelerates the morphology transition process.