Polyelectrolyte-based electrorheological materials

Preparation of layered carbon nitride/titanium-based metal skeleton materials and study on their electrorheological properties

Background: as an intelligent material, electrorheological fluids (ERFs) comprise a suspension system consisting of dielectric particles and/or their composites dispersed in an insulating liquid. In this article, MOF/g-C3N4 composite nanoparticles were successfully synthesized and demonstrated an excellent ER effect. Methods: first, the precursor for g-C3N4 was synthesized using a high-temperature calcination method, followed by the in situ synthesis of MIL-125 (MOF-Ti) on the surface of layered graphitic carbon nitride using a solvothermal approach. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were used to reveal the presence of numerous MOF particles deposited onto the surfaces of layered g-C3N4 nanosheets. X-ray powder diffraction confirmed the growth of MOF particles on the g-C3N4 precursor. The chemical composition and states were characterized through Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron (XPS) analyses. Additionally, BET analysis indicated the presence of abundant pore structures in the MOF/g-C3N4 composite nanoparticles. Results: lastly, rheological and dielectric properties were investigated. The ER behavior demonstrated their excellent performance, with a 10 wt% mass fraction suspension of the MOF/g-C3N4-0.4 based composite material and dimethyl silicone oil exhibiting a yield stress of 300 Pa at 2 kV mm-1.

Highly Porous Particles of Cellulose Derivatives for Advanced Applications

A chemical modification of cellulose diacetate by phthalate and nitrate was performed to increase solubility in organic solvents and change the electrical properties. The role of substituents on the conductivity, permittivity, and polarizability of cellulose films is revealed. It has been shown that highly porous micro particles can be obtained from cellulose derivatives by a simple and technological freeze-drying method. The resulting micro sized aerogels have a predominantly spherical morphology and amorphous structure. Suspensions of porous particles of nitro- and phthalylated cellulose derivatives in silicone oil have an increased dielectric permittivity compared to cellulose diacetate particles. Produced particles are novel promising material with tunable electrical properties for advanced applications in composites, including for electrorheological fluids.

Enhanced Electrorheological Performance of Core-Shell-Structured Polymerized Ionic Liquid@Doubly Polymerized Ionic Liquid Microspheres Prepared via Evaporation-Assisted Dispersion Polymerization

A polymerized ionic liquid (PIL) provides a platform for the development of a high-performance water-free polyelectrolyte-based electrorheological fluid (ERF) because of the presence of large-size hydrophobic ion pairs. However, the large-size hydrophobic ion pairs also easily result in a low glass-transition temperature of an ordinary linear PIL, and consequently, the PIL-based ERF has to be subject to a high leaking current density and a narrow working temperature range. In this paper, we prepared a kind of core-shell-structured polymerized ionic liquid@doubly polymerized ionic liquid (PIL@D-PIL) microsphere with a linear PIL as the core and a physically cross-linked D-PIL as the shell via an evaporation-assisted dispersion polymerization method. The core-shell structure of the sample was observed by scanning electron microscopy and transmission electron microscopy. The thermal properties of the sample were tested by differential scanning calorimetery and thermogravimetric analysis. The ER effect and dielectric polarization of PIL@D-PIL microspheres when dispersed in an insulating nonpolar liquid were studied by a rheometer and dielectric spectroscopy. It shows that the glass-transition temperature and thermal stability of a PIL increased after coating with the D-PIL shell. Under electric fields, the ERF of the PIL@D-PIL microspheres exhibits a significantly reduced leaking current density and an enhanced operating temperature range compared to the ERF of single-PIL microspheres. The PIL@D-PIL microspheres can still maintain good ER effect even if the temperature is higher than the glass-transition point of the PIL core due to the protection of the D-PIL shell.