ABSTRACT
Electrokinetic properties such as the mobility, surface charge, and zeta potential of sub-millimeter particles are vital parameters in various industrial applications. Their measurement and control in aqueous media have been extensively studied. However, despite their growing importance, the electrokinetic properties of organic solvents have not been studied as thoroughly as those of aqueous media. An electrophoresis cell with a microscope monitor was designed for the electrokinetic studies of sub-millimeter particles in cyclohexane, which is a solvent with very low permittivity. The movement of large particles in the range of 4 ~ 478 µm was successfully traced under a strong electric voltage up to 1100 V, even without the addition of surfactants. The particle sizes were at least 300 times larger than those reported previously. By applying electric fields up to 55 kV/m, the electrophoretic mobilities were measured to be of the order of 10-9 to 10-7 m2/Vâs through image processing of the recorded particle movement. Five organic sub-millimeter particles had charge densities in the range of -3.5 ~ 4.4 e/µm2, and polyethersulfone particles showed extremely high mobilities. The surface charge of organic and inorganic particles is mainly generated by the dissociation of hydroxide groups or by the protonation to surface Lewis base oxygen atoms.
Subject(s)
Electricity , Surface-Active Agents , Electrophoresis/methods , Particle SizeABSTRACT
The complicated chemical vapour deposition (CVD) is currently the most viable method of producing graphene. Most studies have extensively focused on chemical aspects either through experiments or computational studies. However, gas-phase dynamics in CVD reportedly plays an important role in improving graphene quality. Given that mass transport is the rate-limiting step for graphene deposition in atmospheric-pressure CVD (APCVD), the interfacial phenomena at the gas-solid interface (i.e., the boundary layer) are a crucial controlling factor. Accordingly, only by understanding and controlling the boundary-layer thickness can uniform full-coverage graphene deposition be achieved. In this study, a simplified computational fluid dynamics analysis of APCVD was performed to investigate gas-phase dynamics during deposition. Boundary-layer thickness was also estimated through the development of a customised homogeneous gas model. Interfacial phenomena, particularly the boundary layer and mass transport within it, were studied. The effects of Reynolds number on these factors were explored and compared with experimentally obtained results of the characterised graphene deposit. We then discussed and elucidated the important relation of fluid dynamics to graphene growth through APCVD.
ABSTRACT
Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth.
