Enhancement of thermal conductivity of titanium dioxide nanoparticle suspensions by femtosecond laser irradiation

This work reports significant increase in the thermal conductivity (k) of aqueous titanium dioxide (TiO2) nanoparticle (NP) suspensions by ultrafast laser irradiation. At relatively low laser fluence (F similar to several tens of mJ/cm(2)), a laser stabilization process occurred, which did not reduce primary particle size, but yielded increase from 1.04 to 1.12 in the thermal-conductivity ratio of the aqueous TiO2 nanoparticle suspension. At relatively high laser fluence (F similar to several J/cm(2)), laser fragmentation of the NPs reduced the primary particle size, and as a consequence k ratio increased to 1.26. Theoretical models that consider the percolation effects of aggregates, Brownian motion, interfacial liquid layering, and formation of electric double layer (EDL), were used to explain the increase in k. This work shows that ultrafast laser irradiation offers an effective non-chemical means to improve the thermophysical and colloidal properties of TiO2 nanofluids. (C) 2018 Elsevier Ltd. All rights reserved.