Experimental investigation on the static and dynamic stability of water-based graphene nanofluids prepared by one-step liquid phase shear exfoliation of graphite

Abstract

Graphene nanofluids show prospects in various applications due to their outstanding optical, thermal, and mechanical properties. However, achieving the long-duration stability of graphene nanofluids prepared by the traditional two-step method is still challenging. Herein, one-step liquid phase shear exfoliation was applied to fabricate stable graphene nanofluids in water from graphite with cetyl trimethyl ammonium bromide (CTAB) as the surfactant. Results indicated that high-quality graphene with multi-layer was fabricated. The graphene production rate depends on CTAB concentration up to 0.25 mg/ml, but beyond that, the graphene concentration almost remains constant (∼18 ppm). Extending the exfoliation time could improve the production rate of graphene nanosheets without sacrificing their quality. The zeta potential of nanofluids prepared at CTAB concentrations of 1 mg/ml and 4 mg/ml is 45–60 mV, demonstrating that the nanofluids exhibit high static stability. Besides, the nanofluids' relative concentration (RC) values are over 0.95 at 20 °C and 40 °C in the flow rate range of 0–1.5 l/min. The nanofluids subjected to static heating at 60 °C are stable; however, their dynamic stability deteriorates gradually with the increasing flow rate because the physically absorbed cationic surfactant more easily falls off from graphene nanosheets, and collision frequency among graphene nanosheets intensifies at high temperatures under the flow condition. Furthermore, high-low temperature cycling could effectively relieve the deterioration of the nanofluids' stability, suggesting that once the electrostatic stabilization effect could be guaranteed by timely cooling, the graphene nanofluids would keep stable.