External electromagnetic field-aided freezing of CMC-modified graphene/water nanofluid

Graphene/water nanofluids with and without surfactant carboxyl methyl cellulose (CMC) were prepared using ultrasonic vibration. Surfactant CMC caused the change in the zeta potential of graphene/water nanofluid from 3.9 mV to -53.1 my. The CIVIC-modified graphene/water nanofluid then froze with and without an external electromagnetic field and melted at room temperature. The particle size distributions and adsorption spectra of graphene/water nanofluid after a freeze/melt cycle at different current intensities were measured to evaluate the electromagnetic field effect on graphene rejection and engulfment by the advancing ice-water interface. Results show that (1) without an electromagnetic field, the absorbance of graphene/water nanofluid dramatically reduces, and a new peak of large particle size emerges after a freeze/melt cycle, thereby indicating that graphenes are partially rejected by the ice-water front and aggregate together; and (2) with an electromagnetic field, the adsorption spectra and the particle size distributions of graphene/water nanofluid do not significantly change after a freeze/melt cycle, thereby indicating that the graphenes are captured by the freezing interface and are uniformly distributed in the frozen body of graphene/water nanofluid. The electromagnetic field effect is closely related to the electric current intensity. Good thermal cycling stability can be achieved for graphene/water nanofluid in the current range of 0.07-0.12 A. Mechanisms associated with surfactant adsorption, electromagnetic field, and possible gas evolution are proposed in this study to account for the behavior of graphenes in front of the ice-water interface. (C) 2015 Elsevier Ltd. All rights reserved.