Silane grafting techniques determine colloidal stability, interfacial and rheological properties of propylene glycol based nanofluids

For engineering applications such as high-heat-flux thermal management, nanofluids must simultaneously exhibit excellent long-term stability and suitable rheological and interfacial properties to meet practical operating requirements. Accordingly, this study investigates TiO 2 /propylene glycol nanofluids and constructs organic grafting layers on TiO 2 surfaces using γ-methacryloxypropyltrimethoxysilane, denoted as KH-570, and n-octyltriethoxysilane, denoted as OTES, to systematically compare the modification effects of the two grafting systems. TGA, FTIR, and TEM analyses confirm the formation of stable grafted layers on TiO 2 , and the grafting efficiency shows a rise–fall trend with increasing silane concentration, with the maximum values reaching 7.954% for KH-570 and 6.268% for OTES. Stability tests indicate that the KH-570-modified nanofluids exhibit superior dispersion stability: over a 50-day quiescent period, the minimum clear-supernatant thickness is 1.205 mm, which is markedly lower than 4.123 mm for the OTES-modified system. Rheological measurements show that at 40 °C over a shear-rate range of 75–450 s -1 , all samples display shear-thinning behavior, and increasing grafting efficiency leads to higher viscosity and more pronounced shear-thinning. In terms of interfacial properties, the introduction of surface functional groups causes the surface tension to decrease significantly with increasing grafting efficiency for both silanes. Based on the experimental data, empirical models were developed for the two modified nanofluids, yielding R 2 values no lower than 0.98 and mean relative errors controlled within 0.247%.