Effect of Fluorophobic Character upon Switching Nanoparticles in Polymer Films from Aggregated to Dispersed States Using Immersion Annealing

Abstract

For nanoparticle (NP) polymer composites, the state of dispersion vs aggregation significantly affects optical, electronic, thermal, and mechanical properties. The switching of NP distribution states thus far was limited to polymer solutions or bulky polymer-grafted NPs. Herein, for the first time, NP distribution states within polymer films are switched by adjusting fluorophobic interactions and the enthalpy of mixing with immersion annealing. The fluorophobic effect is the tendency of fluorinated molecules to strongly phase-separate from non/less fluorinated molecules. A highly fluorophobic homopolymer, poly­(perfluorooctyl acrylate) (PFOA), was combined with gold NPs of variable fluorophobic character, prepared using mixtures of small-molecule ligands (xF-NP, where x is the mol % fluorinated ligands). Low-to-moderately fluorophobic F-NPs with PFOA were aggregated after spin coating where film swelling via immersion annealing with moderately fluorophobic trifluoro toluene (TFT) generally led to a dispersed state. In contrast, the highly fluorophobic 100F-NPs were dispersed regardless of immersion annealing. This behavior was attributed to the PFOA acting like a surfactant to enable dispersion of highly fluorophobic NPs in TFT. Since these two distinct behaviors favor nonoverlapping ranges of xF-NP compositions, the NPs with intermediate compositions exhibited limited dispersibility. This fluorophobic switchability could enable time- and chemical-selective sensing of fluorinated compounds in the future.

Nanogel Degradation at Soft Interfaces and in Bulk: Tracking Shape Changes and Interfacial Spreading

“…Since nanogels and microgels are soft polymer networks with characteristic linear sizes of the order of tens to hundreds of nanometers to tens of microns, respectively, mesoscale modeling approaches are commonly used to capture their behavior in solvents and at the interfaces. Dissipative particle dynamics (DPD), − a mesoscale approach that has been used for modeling a broad range of multi-component systems, − is often chosen to model behavior of microgels at liquid–liquid interfaces. ,,,− To model controlled degradation and erosion in hydrogels, we recently adapted a modified segmental repulsive potential (mSRP) to overcome unphysical crossing of polymer chains along with modeling of degradable bonds. , As a model polymer network, we focused on gels synthesized by the end-linking of four-arm polyethylene glycol (PEG) precursors − originally fabricated by Sakai et al. These precursors can be modified during their synthesis by including photodegradable functional groups, for example, nitrobenzyl − or coumarin , groups.…”