Effect of nanoscale confinement on glass transition of polystyrene domains from self-assembly of block copolymers.

The understanding of size-dependent properties is key to the implementation of nanotechnology. One controversial and unresolved topic is the influence of characteristic size on the glass transition temperature (Tg) for ultrathin films and other nanoscale geometries. We show that Tg does depend on size for polystyrene spherical domains with diameters from 20 to 70 nm which are formed from phase separation of diblock copolymers containing a poly(styrene-co-butadiene) soft block and a polystyrene hard block. A comparison of our data with published results on other block copolymer systems indicates that the size dependence of Tg is a consequence of diffuse interfaces and does not reflect an intrinsic size effect. This is supported by our measurements on 27 nm polystyrene domains in a styrene-isobutylene-styrene triblock copolymer which indicate only a small Tg depression (3 K) compared to bulk behavior. We expect no effect of size on Tg in the limit as the solubility parameters of the hard and soft blocks div...