Switching between negative and positive electrorheological effect of g-C 3 N 4 by copper ions doping

Abstract

Investigation of pristine g-C 3 N 4 and copper ions doped g-C 3 N 4 as dispersed phases in silicone-oil based electrorheological (ER) fluids is reported for the first time. Pristine g-C 3 N 4 was prepared via standard thermal polycondensation of urea. Introduction of Cu ions into g-C 3 N 4 polymeric network was performed by treatment of pristine powder by a solution containing tetraammoniumdiaquacopper(II) complex ions followed by annealing. The structure and properties of products were revealed with the aid of XRD, FTIR, UV–Vis and XPS, and complemented by SEM investigation of morphology, pycnometry, BET analysis, and conductivity measurements. The response of prepared ER fluids to an external electric field was examined by rheometry and the effects visualized with optical microscopy. While ER fluids based on g-C 3 N 4 exhibited negative ER effect (decrease in viscosity when the field is switched-on), ER fluids based on a g-C 3 N 4 /Cu-doped analogue exhibited positive ER effect. Dielectric spectroscopy using Havriliak-Negami model revealed that introduction of the dopant almost doubled the dielectric relaxation strength while the relaxation time was halved. The ability of g-C 3 N 4 /Cu as a candidate for further studies necessary to increase the ER effect was demonstrated. Thereto, described modification of g-C 3 N 4 by copper ions shall be applicable also for other metals forming ammonia complexes. © 2019 The Society of Powder Technology Japan