حميدرضا حسنلو

Owing to its severe hydrophobicity, graphene (G) as on dispersed in a fluid usually deposits there in after a short interval of time. Understanding the G-behavior and the factors affecting its deposition could pave a way of creating a substantially stable nanofluid (NF). In this work, a novel method of stabilizing a G-NF is described with selective examples. The results can be extended to develop science and technology of G-NFs in general. Electrohydrodynamic forces are used as a controlling factor in the presence of magnetic nanoparticles (MNPs). Contrary to common chemical methods employed for preparing G-NFs, which depend on establishing bonds between the components, the physical method introduced in this article could be used as a novel approach not only to dispersing G in a fluid carrier, but also to resolve the common problems originating from utilizing such chemical methods as increasing thermal resistance through adding various types of surfactants. The effects of various factors on the stability of the G-NFs are described. By increasing 50%, 100% and 170% of G, the G sitting rate increased by 43%, 82%, and 109%, respectively. With the addition of one, two and three layers to a G-monolayer, the G sitting rate grew by 77%, 153%, and 263%, respectively. Further, the G-behavior in the presence of MNPs and varied intensive electric fields were studied to optimize an electric field that could stabilize a single-layer G sheet in aqueous NFs. Adding MNPs pro‎mp‎tly stabilizes a water/ethylene glycol/G NF in an applied electric field of 0.05 V/Å. In addition, effect of adding Sodium dodecyl benzenesulfonate(SDBS), Sodium dodecyl sulfate (SDS) and Triton X-100 on the thermophysical properties and the stability of water/ethylene glycol-G NFs is investigated. The results of this study can be used to produce G-NFs with optimized thermophysical properties and stability by using appropriate surfactants. Final observations demonstrate that NFs with Triton X-100 have the highest viscosity and the lowest diffusion coefficient. Benzene ring and a stronger bond between G and SDBS make the SDBS NFs more stable. All in all, the thermophysical properties of NFs are influenced more than their stability by adding surfactants. The best thermophysical improvement was found for NFs prepared with SDS anionic surfactant. On the other hand, NFs with SDBS surfactant has a better stability. Keywords: Graphene stability; Electrohydrodynamic force; Thermophysical properties; Non-covalent functionalization; Reactive molecular dynamics.