Shear thickening behavior and thermal properties of nanofluids with graphite fillers

This paper shows the thermal conductivity and rheological properties of shear thickening fluids (STF) containing two hybrid fillers which are expanded or intercalated graphite and silica oxide dispersed in poly(propylene glycol). Unique characteristics of STF with enhanced capacity of energy dissipation in combination with increased modulus of elasticity make these fluids the right solution for damping and shock absorption. Unfortunately, at an elevated temperature, the efficiency of the composite is weaker. Utilizing graphite as a heat diffusion promoter it aims to ensure faster heat dissipation from STF at higher temperature and its immediate return to the initial state, wherein the dilatant effect is the most efficient. The study was focused on increasing the thermal diffusivity of the composite materials by increasing the filler content added in excess to STF or as a partial substitute of solid phase in amount of 1%, 3%, 5% and 10% by volume at T1 = 25 °C, T2 = 36 °C, T3 = 50 °C, T4 = 75 °C and T5 = 100 °C. It was found that the expanded graphite (EG) filler had a great influence on the effective thermal conductivity of the composite materials. From the rheological point of view the sample with 3%vol. EG in excess was selected as the most favorable one for shock absorbing systems. The dilatant effect for this sample in comparison with reference sample without the thermal promoter was 5 times higher at 30 °C and about two times higher at 50 °C and 75 °C. This result is very promising in further design of absorbing systems.