Electro-responsive Characteristics of Carbon Nanomaterials with Inorganic Coating for Smart Composites

Abstract

The inorganic-coated carbon nanomaterials with anisotropic core-shell structure were fabricated for electrorheological (ER) fluid as well as the fiber webs encapsulating ER fluid were produced via a coaxial electrospinning technique for instantly hardening material. First, Multi-walled carbon nanotubes (MWNTs) were used to the template for the fabrication of one dimensional nanomaterials with adequate electrical conductivity (10-7~10-9 S/cm) and high elastic modulus. Silica-coated MWNTs (S-MWNTs) and titania-coated MWNTs (T-MWNTs) with cylindrical structure were synthesized to investigate the ER effects of inorganic materials with different dielectric constant. The electrorheological and dielectric properties of the two different inorganic-coated MWNTs ER fluids were measured using the rheometer and impedance analyzer. The T-MWNTs ER fluids have shown higher dynamic yield stress as well as viscoelastic properties compared to the S-MWNTs ER fluids under external electric field. Furthermore, the T-MWNTs ER fluids have shown higher permittivity and shorter relaxation time of interfacial polarization than those of S-MWNTs. It was caused by intrinsic properties of different inorganic materials which used as shell material. Second, we prepared S-MWNTs with three different shell thickness and inorganic-coated MWNTs with double layer to modify dielectric properties and electrical conductivity of MWNTs. The electrical conductivity of S-MWNTs decreased with an increase of the shell thickness. However, the dynamic yield stress and viscoelastic properties of S-MWNTs suspension increased with an increase the shell thickness and then decreased to the shell thickness 40 nm. This indicates that the electrical conductivity of particles is an important parameter in the ER performance. In the case of ER fluids with double layer, the dynamic yield stress of silica-titania-coated MWNTs (ST-MWNTs) suspension was higher compared to titania-silica-coated MWNTs (TS-MWNTs) suspension at the same volume fraction. It has been found that the outermost shell material plays an important role in the ER performance. Third, titania-coated graphene sheets (TCGSs) were synthesized by a sol-gel method to investigate influence of the difference between 1D and 2D structure and the mixture of T-MWNTs and TCGSs fluids. The value of TCGSs suspension was 2.11, which is similar to the T-MWNTs based ER fluids (2.17). However, the relaxation time of T-MWNTs is faster than that of TCGSs. This is caused by the degree of entanglement and specific surface area between T-MWNTs and TCGSs. Furthermore, mixture effect of T-MWNTs and TCGSs suspension on ER and dielectric properties has been analyzed. The mixture suspension showed the good stability of standing, the enhanced ER performance due to a unique interconnected nanostructure with high contact points and a large surface area, which shows a synergic effect and improves the interfacial interaction between inter-particles and conducting 3D network. Finally, fiber mats composed inorganic-coated MWNTs ER fluids as core part and poly(ethylene terephthalate) (PET) as shell component were produced using co-axial electrospinning technique for instantly hardening textile. The effect of core particle concentration and external field strength on mechanical properties of fiber mats was investigated. The modulus and tensile strength of the fiber mats is enhanced as well as the breaking elongation is reduced under the external electric field due to the increase of fibrillation number in core part.