Dewetting of Star Nanogel/Homopolymer Blends from an Immiscible Homopolymer Substrate

Direct observation of interfacial C60 cluster formation in polystyrene-C60 nanocomposite films

Large interfacial C(60) clusters were directly imaged at the supporting film-substrate interface in physically detached polystyrene-C(60) nanocomposite films by atomic force microscopy, confirming the stabilizing mechanism previously hypothesized for thin polymer films. Additionally, we found that the C(60) additive influences basic thermodynamic film properties such as the interfacial energy and the film thermal expansion coefficient.

Autophobicity-driven surface segregation and patterning of core-shell microgel nanoparticles

Core-shell microgel (CSMG) nanoparticles, also referred to as core-cross-linked star (CCS) polymers, can be envisaged as permanently cross-linked block copolymer micelles and, as such, afford novel opportunities for chemical functionalization, templating, and encapsulation. In this study, we explore the behavior of CSMG nanoparticles comprising a poly(methyl methacrylate) (PMMA) shell in molten PMMA thin films. Because of the autophobicity between the densely packed, short PMMA arms of the CSMG shell and the long PMMA chains in the matrix, the nanoparticles migrate to the film surface. They cannot, however, break through the surface because of the inherently high surface energy of PMMA. Similar thermal treatment of CSMG-containing PMMA thin films with a polystyrene (PS) capping layer replaces surface energy at the PMMA/air interface by interfacial energy at the PMMA/PS interface, which reduces the energy barrier by an order of magnitude, thereby permitting the nanoparticles to emerge out of the PMMA bulk. This nanoscale process is reversible and can be captured at intermediate degrees of completion. Moreover, it is fundamentally general and can be exploited as an alternative means by which to reversibly pattern or functionalize polymer surfaces for applications requiring responsive nanolithography.

Control of dispersion state of silsesquioxane nanofillers for stabilization of polystyrene thin films

The influence of the dispersion states of the nanofillers on the dewetting behavior of the polymer thin film was investigated. Polyhedral oligomeric silsesquioxanes (POSS) with various substituents were added into polystyrene (PS) thin films as the nanofillers. The dewetting rate of the films drastically changed with the surface substituents of POSS additives. Neutron reflectivity measurements indicated that the difference of the dewetting rate was associated with the dispersion state of POSS additives in the films. POSS with phenethyl groups (PhPOSS), which homogeneously dispersed into the films, resulted in the decrease of the glass transition temperature of PS and the enhancement of the dewetting of the films. POSS with a fluoroalkyl group (CpPOSS-R f) segregated to the film surface and showed the retardation of the dewetting by the decrease of the surface energy of the film. POSS with hydroxyl groups (CpPOSS-2OH) segregated to the film surface and film-substrate interface and led to the elimination of the dewetting, suggesting the importance of the interfacial segregation for the inhibition of dewetting. These results revealed the strong relationship between the dispersion state of the nanofillers and the dewetting of the nanofilled films.