Bespoke Block Copolymer Nanoparticles Boost the Thermal Conductivity of Oils

Abstract

Next-generation thermal management fluids are urgently required for the efficient cooling of data centers and fast-charging batteries. To address this problem, we have prepared diblock copolymer nanoparticles with polar cores in non-polar media using polymerization-induced self-assembly (PISA). This is achieved via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) using an oil-soluble poly(lauryl methacrylate) (PLMA) precursor in a poly(α-olefin) oil. This synthetic protocol affords a low-viscosity dispersion of PLMA–PHEMA nanoparticles of approximately 100 nm diameter at up to 30% w/w solids. The PHEMA cores of such nanoparticles can be swollen with aqueous acid without any loss of colloidal stability, as judged by dynamic light scattering. Such acid-swollen nanoparticles serve as nanoreactors for the in situ synthesis of silica using an oil-soluble precursor (tetraethyl orthosilicate, TEOS). Thermogravimetric analysis reveals that the resulting nanocomposite nanoparticles contain up to 27% silica by mass. Extensive thermal conductivity measurements have been performed as a function of copolymer concentration, aqueous acid content, and temperature on the as-prepared PLMA–PHEMA nanoparticle dispersions, the acid-swollen nanoparticles, and the silica-loaded nanoparticles. The as-prepared nanoparticles boost thermal conductivity by up to 6.0%, with minimal increase in the kinematic viscosity of the dispersion. The addition of aqueous acid and the in situ formation of silica within the nanoparticle cores lead to further enhancements in thermal conductivity. Interestingly, colloidal dispersions of the silica-loaded nanocomposite nanoparticles can be engineered to be highly transparent at a given temperature, which could be an important advantage for their potential use as a next-generation thermal management fluid.