Electrorheological Fluids of GO/Graphene-Based Nanoplates

Due to their unique anisotropic morphology and properties, graphene-based materials have received extensive attention in the field of smart materials. Recent studies show that graphene-based materials have potential application as a dispersed phase to develop high-performance electrorheological (ER) fluids, a kind of smart suspension whose viscosity and viscoelastic properties can be adjusted by external electric fields. However, pure graphene is not suitable for use as the dispersed phase of ER fluids due to the electric short circuit caused by its high electrical conductivity under electric fields. However, graphene oxide (GO) and graphene-based composites are suitable for use as the dispersed phase of ER fluids and show significantly enhanced property. In this review, we look critically at the latest developments of ER fluids based on GO and graphene-based composites, including their preparation, electrically tunable ER property, and dispersed stability. The mechanism behind enhanced ER property is discussed according to dielectric spectrum analysis. Finally, we also propose the remaining challenges and possible developments for the future outlook in this field.

Strong Electrorheological Performance of Smart Fluids Based on TiO2 Particles at Relatively Low Electric Field

Electrorheological (ER) fluids are a type of smart material with adjustable rheological properties. Generally, the high yield stress (>100 kPa) requires high electric field strength (>4 kV/mm). Herein, the TiO2 nanoparticles were synthesized via the sol–gel method. Interestingly, the ER fluid-based TiO2 nanoparticles give superior high yield stress of 144.0 kPa at only 2.5 kV/mm. By exploring the characteristic structure and dielectric property of TiO2 nanoparticles and ER fluid, the surface polar molecules on samples were assumed to play a crucial role for their giant electrorheological effect, while interfacial polarization was assumed to be dominated and induces large yield stress at the low electric field, which gives the advantage in low power consumption, sufficient shear stress, low leaking current, and security.

Research on shear stress of electrorheological fluid containing piezoelectric powders

This paper describes experimental trials that were performed to increase the electrorheological (ER) effect in ER fluids (ERFs) by introducing piezoelectric particles (PEPs). Five sample solutions were made using different PEPs, ER powders, and liquids that included ERFs provided with different solutions and silicone oil. The shear stress of each sample was measured by shearing the sample between parallel plate electrodes. Samples containing the PEP showed the same shear stress under steady voltage inputs but showed somewhat higher shear stress under sinusoidal voltage inputs. This suggests that mixtures of the piezoelectric powders (at approximately 5 wt.%) and the ERF may shorten the response time of the ERF to DC inputs or increase the response frequency to AC inputs.

Investigation of vibration damping properties of electroactive polyanthracene/silicone oil dispersions

Electrorheological (ER) fluids generate mechanical responses to applied electric field strength via changing their rheological properties from liquid to solid and vice-versa reversibly. As a result of this, ER fluids can be used in the industrial vibration damping systems. In order to increase applicability of ER fluids, it is necessary to understand electric field induced polarization and ER mechanism of different materials. Therefore, the aim of this study is to illuminate ER and vibration damping properties of polyanthracene (PAT), which is a new material for ER studies. PAT was synthesized from anthracene and characterized by several techniques namely: ATR-FTIR spectroscopy, particle size, SEM image, four-point probe conductivity, and magnetic susceptibility measurements. A series of PAT/silicone oil (SO) dispersions having various concentrations were prepared and subjected to dielectric and ER tests. Then, the colloidal stabilities of 20% PAT/SO and 20% PAT/SO/TritonX systems were determined. Dynamic viscoelastic data obtained by the oscillation tests showed that viscous behavior was dominant under zero electric field, whereas elastic behavior was prevailing under external electric field strength and highlighting the vibration damping characteristics of PAT/SO dispersion. In the creep-recovery measurements, the highest %recovery was recorded to be 62% indicating potential industrial use of PAT/SO dispersion.

The Electric Field Responses of Inorganic Ionogels and Poly(ionic liquid)s

Ionic liquids (ILs) are a class of pure ions with melting points lower than 100 °C. They are getting more and more attention because of their high thermal stability, high ionic conductivity and dielectric properties. The unique dielectric properties aroused by the ion motion of ILs makes ILs-contained inorganics or organics responsive to electric field and have great application potential in smart electrorheological (ER) fluids which can be used as the electro-mechanical interface in engineering devices. In this review, we summarized the recent work of various kinds of ILs-contained inorganic ionogels and poly(ionic liquid)s (PILs) as ER materials including their synthesis methods, ER responses and dielectric analysis. The aim of this work is to highlight the advantage of ILs in the synthesis of dielectric materials and their effects in improving ER responses of the materials in a wide temperature range. It is expected to provide valuable suggestions for the development of ILs-contained inorganics and PILs as electric field responsive materials.

Fabrication, Experiment, and Simulation of a Flexible Microvalve-Integrated Microarm for Microgrippers Using Electrorheological Fluid

Because of the power density advantages of fluid power systems, many researchers have developed microactuators using homogeneous electrorheological (ER) fluids (ERFs) for applications to various micromachines. An ER valve, as a critical component of the ER actuator, can control ERF flow by the apparent viscosity increase resulting from the applied electric field without any mechanical moving parts. Hence, it is adequate for the miniaturization of a fluidic microactuator. However, it is not easy to integrate rigid ER valves into soft microrobots. To overcome these limitations, we developed a novel elastic ER microarm using flexible ER valves (FERVs) in this study. Each microarm consists of an FERV, a movable chamber, and a displacement constraint element, so that it bends with the inner pressure controlled by the FERV. We proposed and developed a micro-electromechanical system fabrication process for the FERV, movable chamber, and displacement constraint element. By utilizing the proposed method, we successfully fabricate a FERV-integrated microarm. The characteristics of the FERV were experimentally clarified. In addition, the bending motion of the FERV-integrated microarm was demonstrated by experiments and verified by finite-element method simulation. This ER microarm was shown to be feasible for an ER microgripper composed of multiple microarms.

Field-structured magnetic elastomers based on thermoplastic polyurethane for fused filament fabrication

The utilization of ‘smart’ materials with adaptable properties or characteristics are a widespread research issue, offering potential for tailored solutions, weight reduction or added value of products through integrated functionality. Therefore, field controlled hybrid materials such as magnetorheological (MR) elastomers or electrorheological (ER) fluids are particularly valuable and within the focus of science and research. At the same time, additive manufacturing has had a strong influence on production processes over the past decade. Today a 3D printer can be found across all disciplines in almost every company, research institution and even in many private households. The Fused Filament Fabrication (FFF) process is especially popular due to its low cost and simplicity. Within this work, a new approach for the generation of field-structured magnetic elastomers using the FFF process and a correspondingly developed prototype print head for implementation are presented and discussed. With its unique research landscape Dresden offers excellent conditions for the development of innovative processes and composite materials in the field of generative manufacture. In the ‘Dresden Concept’ network, experts from various disciplines collaborate and investigate the entire spectrum starting from biological materials, through lightweight fibre reinforced polymer composites, to high-temperature ceramics. This article is part of the theme issue ‘Patterns in soft and biological matters’.

Graphene Oxide and Its Inorganic Composites: Fabrication and Electrorheological Response

Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the fabrication mechanisms of GO/inorganic composites and their ER response when suspended in a non-conducting medium, including steady shear flow curves, dynamic yield stress, On-Off tests, and dynamic oscillation analysis. Furthermore, the morphologies of these composites, dielectric properties, and sedimentation of the ER fluids are covered.