Elucidating the Ligand-induced Phase Behavior of Polymer-grafted Nanoparticle Thin Films
High molecular mass polymer-grafted nanoparticles (PGNPs) have attracted significant attention in the past few decades with the potential to design next-generation polymer nanocomposites with enhanced optical and mechanical properties and thermal stabilities. A critical requirement for these new nanoparticles and their associated applications is the control of their morphology and the dispersion in the system. However, subsequent studies have demonstrated that the mobilities of the high molecular mass PGNPs decrease significantly, which leads to poor or no control over their phase morphologies. In this study, we aim to overcome this scientific problem and control the spatial organization of those materials via the interactions between the grafted polymer layer and the polymer matrix in both smooth and nanopatterned films. We firstly investigate a binary high molecular mass PGNPs blends using a direct immersion annealing method (DIA) that allows for facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient ‘aging’ time. We show that the phase morphologies could be readily switched between phase-separated and homogenous states by changing the thermodynamic conditions of DIA solution quality. To overcome the low-mobility problem and exert exquisite control over the distribution of high molecular mass PGNPs in a nanopatterned film, we developed a solvent vapor annealing soft lithography (SVA-SL) method. We revealed that the minimization of the entropic free energy from the topographic nanoimprint patterning along with the increased mobilities from solvent vapor drives the high molecular mass PGNPs to the ‘mesa’ region of nanopatterned films. Furthermore, reversible partitioning (selective vs. no partitioning) in a nanopatterned film can be facilely achieved by introducing enthalpic interactions into the system. Both the SVA-SL processing method and the reversible partitioning via tunning the interaction parameter are important. It allows for facile imprint patterning of PGNP materials and large-scale organization of the “sluggish” high molecular mass PGNPs. These approaches, along with the DIA method to control the morphologies of smooth film, have great potential to design the nanocomposite films with the enhanced thermo-mechanical property of the resulting films, and a corresponding extended range of potential nanotech applications.