Overcoming thermal instability of polymeric Core-Shell-Particles: Advanced processing options for the preparation of Stimuli-Responsive structural color materials

Abstract

Core-shell particles (CSP) represent one of the most promising building blocks for the artificial production of stimuli-responsive materials with iridescent structural colors. Despite tremendous efforts in the past two decades, scalable processing options for CSP are overall rare and mostly limited to 2D structures in the form of films and foils. This work investigates why common large-scale polymer-processing techniques, such as injection molding or fused filament fabrication, are hardly applicable to state-of-the-art CSP: While rheological prerequisites are fulfilled, thermal stability is proven to be surprisingly poor. Temperature instability during processing is caused by a thermally induced cross-linking reaction of residual reactive moieties. This undesired cross-linking reaction can be efficiently suppressed via optimizations of the particle architecture, in terms of adjusting the core-to-shell ratio and number of grafting anchors. Thermal stability can be further increased upon incorporation of primary antioxidants. The theoretical framework and the feasibility of the developed solution strategies are verified by a variety of thermoanalytical methods, including differential scanning calorimetry, thermogravimetric analysis, as well as rheological and mechanical measurements. Finally, advanced CSP are developed and demonstrated to be conveniently processable at elevated temperatures of up to 250 °C. These next-generation CSP formulations are advantageous for established processing techniques and may further pave the way for the design of new large-scale methods suitable for industrial use. Potential applications are smart sensors, advanced display technologies, or anti-counterfeiting materials.