Interface and Morphology Control of the Thermal Conductivity in Core–Shell Particle Colloidal Crystals

Abstract The thermal transport properties of nanostructured composite colloidal assemblies are investigated. These are of importance for future phase change material applications, which increasingly address the micrometer and sub‐micrometer ranges. Polystyrene silica core–shell colloidal particles sizes of 270–480 nm and shell thicknesses of 15–42 nm are used as a structurally well‑defined model system. This allows deducing precise structure property relationships with the lowest thermal conductivity being observed for particles with a large diameter, a thin shell thickness, and the highest polymer content. Importantly, clear evidence is found for polymer leakage through 15 nm silica shells when exceeding the glass transition temperature of the core polymer. This leads to a steady increase in thermal conductivity but also presents a lower limit for the silica shell thickness to contain the second phase. For a complete understanding, the findings are discussed in the light of colloidal crystals consisting of pure silica and polystyrene particles. Solid silica sphere colloidal crystals possess the highest thermal conductivity, and pure polymer beads the lowest. This demonstrates to which extent the thermal transport properties can be solely adjusted by the particle composition and morphology.