Thickening of liquids using copolymer grafted nanoparticles†

Precise control over the flow behavior of liquids is a critical problem and is demanding for multifaceted applications. Introducing surface-engineered nanoparticles into the liquid can tune the flow behavior. However, the extent of tunability depends on the compatibility of the surface groups on nanoparticles and the liquid matrix. Herein, we report a strategy to synthesize solvophilic surface-engineered nanoparticles demonstrating its capability to control the flow properties of chemically distinct liquids like silicone oil and polyethylene glycol. Silylated polyether amine-modified silica nanoparticles with a polymer brush-like structure are selected as the model synthesized material. By combining rheological experiments with coarse-grained molecular dynamics (CGMD) simulations, we demonstrate that adding these grafted nanoparticles significantly impacts the viscosity of both liquids. The impact of grafting density on the rheological properties was also corroborated. Simulations indicate the formation of a diverse array of nanoparticle microstructures, including contact aggregates, bridged aggregates, and one-dimensional string-like structures dictate the viscosity of the material. Furthermore, we show that copolymers with predominantly matrix-compatible moieties facilitate the intercalation of matrix molecules within the polymer brushes, enhancing interactions at the molecular level. This work provides a novel microstructural mechanism for tuneable rheological properties, offering new pathways for optimizing liquid formulations.