Surface and Interfacial Activity of Polymer Thin Films Induced by Block Copolymers and Microgel Nanoparticles

Molecularly-thin polymer films that remain stable on solid substrates hold tremendous promise for a wide variety of contemporary applications. Understanding the factors that promote the destabilization of polymer thin films is critical for the design of stable molecularly-thin coatings to be used in a wide range of technologies.;In order to develop a molecular-level understanding of how the soft modifiers influence the stability polymer thin film, we focused on the surface-anchored PS-b-PMMA block copolymers with various chemical compositions and core-shell microgel nanoparticles. By altering the chemical composition of surface-anchored PS-b-PMMA, the dewetting mechanism of top PS thin films undergoes the evolution from spinodal dewetting, dual occurrence (spinodal dewetting and nucleation and growth dewetting) to nucleation and growth dewetting.;We further examined the stability of this nanoparticles thin film in several ways. Upon annealing above the Tg of the chemical species in this CSMG nanoparticles, it shows the extreme thermal stability and the thin film keep wetted on the silica surface. By introducing two silanes to eliminate the possible interaction between the core and silica substrate, the CSMG thin film keeps stable. More interestingly, the CSMG thin film can be floated on DI water and keeps intact with the fact that M w (11 kDa) of PS arm is lower than the entanglement Mw (18 kDa) of PS homopolymer.;In parallel with surface-anchored PS-b-PMMA studies, core-shell microgel (CSMG) nanoparticles was also used to modify the silica substrate to investigate the instability of PS thin film above. By directly spin-coating the PS homopolymer onto the pre-annealed CSMG thin film, the PS thin film undergoes the inversed the dewetting behaviors in a certain Mw range, due to the self-assembled structure formed on CSMG thin film surface during spincoating.;Likewise, CSMG nanoparticles were used as the nano-filler to incorporate into the PS 50 kDa thin film. By altering the amount of CSMG loading and film thickness, PS50/CSMG thin film undergoes the transition from spinodal dewetting to nucleation and growth dewetting. The surface heterogeneity induced by anchoring and aggregation of CSMG on silica substrate during annealing triggers this mechanistic transition.;Lastly, we have examined the morphologies of MG nanoparticles in various deposition methods. Sonication was applied to MG diluted solution to inhibit the aggregation before positioning MG on substrate. The result indicates that pre-sonication can sufficiently inhibit MG aggregation on silica substrate. Also, the aggregated morphologies of MG nanoparticles deposited by electrospraying indicated the convective air flow may accelerate the evaporation of small liquid droplets from tiny needle of the syringe, even the diluted solution was pre-sonicated. More interestingly, 2D string-liked nano-scaled self-assembly of MG nanoparticles was discovered by drop-casting of pre-sonicated diluted solutions on silica substrate.