Modification of polymer/polymer interfaces using block copolymers and microgels

A guest macromolecule, consisting of either a block copolymer (BCP) or core-shell microgel (MG) particles, has been used to stabilize a polystyrene (PS) film positioned atop a substrate of poly(methyl methacrylate) (PMMA) homopolymer, which is immiscible with PS. Modification of the PS/PMMA interface due to interfacial partitioning of the guest macromolecule significantly increases the stability of the PS film by either slowing down or completely eliminating dewetting of the top PS layer. It has been established that the PS dewetting rate depends on (i) the concentration of guest macromolecule, (ii) the PS film thickness and (iii) the annealing temperature. In general, the dewetting rate is observed to decrease with increasing BCP or MG concentration.; Our work has revealed that the dewetting mechanism of the top layer may change between nucleation and growth of holes and spinodal-like surface fluctuations, depending on the extent of interfacial heterogeneities induced by the BCP at the PS/PMMA interface. At relatively low BCP and MG concentrations, high-temperature dewetting occurs by nucleation and growth of circular holes. Within this regime, accelerated hole growth is also observed as the BCP concentration is increased. A further increase in BCP concentration yields spinodal-like dewetting due to modification of the PS/PMMA interface by individual BCP molecules and micelles. At still higher BCP concentrations, the dewetting mechanism switches back to nucleation and growth of holes, albeit of irregular (non-circular) shape. The top film completely stabilizes (no dewetting is observed) when a sufficiently high level of BCP is added.; Due to the shape retention of the MG autophobicity is observed between the MG particles with a PS-like core and PMMA arms and a chemically identical long-chain PMMA homopolymer. This behavior is attributed to entropic exclusion of the PMMA matrix polymer from the high graft density of PMMA arms. In agreement with theoretical predictions, the change in free energy (DeltaFauto ) due to autophobic segregation of MG from the PMMA matrix is of the same order as typical polymer/polymer interfacial energy (gammaAB), but about an order of magnitude lower than typical polymer surface energy (gammaA or gammaB). By positioning a thin layer of PS on top of a PMMA/MG film, we have demonstrated that autophobicity is strong enough to overcome the resistance of gammaAB so that the MG could be pushed from the PMMA matrix to the PS/PMMA interface. (Abstract shortened by UMI.)...