Control of Phase Morphology of Binary Polymer Grafted Nanoparticle Blend Films via Direct Immersion Annealing

While the phase separation of binary mixtures of chemically different polymer-grafted nanoparticles (PGNPs) is observed to superficially resemble conventional polymer blends, the presence of a soft polymer-grafted layer on the inorganic core of these nanoparticles qualitatively alters the phase separation kinetics of these nanoblends from the typical pattern of behavior seen in polymer blends and other simple fluids. We investigate this system using a direct immersion annealing method (DIA) that allows for a facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient aging time. In particular, by switching the DIA solvent composition from a selective one (which increases the interaction parameter according to Timmerman's rule) to an overall good solvent for both PGNP components, we can achieve rapid switchability between phase-separated and homogeneous states. Despite a relatively low and non-classical power-law coarsening exponent, the overall phase separation process is completed on a time scale on the order of a few minutes. Moreover, the roughness of the PGNP blend film saturates at a scale that is proportional to the inplane phase separation pattern scale, as observed in previous blend and block copolymer film studies. The relatively low magnitude of the coarsening exponent n is attributed to a suppression of hydrodynamic interactions between the PGNPs. The DIA method provides a significant opportunity to control the phase separation morphology of PGNP blends by solution processing, and this method is expected to be quite useful in creating advanced materials.

Automated summary

The phase separation of binary mixtures of polymer-grafted nanoparticles (PGNPs) with a soft polymer-grafted layer on the inorganic core exhibits different kinetics from conventional polymer blends, and can be controlled by switching the solvent composition. Despite a relatively low coarsening exponent, the phase separation process is completed within minutes and the roughness of the blend film saturates at a scale proportional to the phase separation pattern scale. The direct immersion annealing method provides a significant opportunity for controlling the phase separation morphology of PGNP blends by solution processing.