Piezoresistive Composites Research Articles

Synthesis and Characterization of Gold Nanostars as Filler of Tunneling Conductive Polymer Composites

AbstractHighly multibranched gold nanostars were obtained by a room‐temperature synthesis assisted by deep‐eutectic solvents (DES). The concentration of the ascorbate ions and the presence of water in the solution were found to both have a profound influence on branch formation. A growth mechanism of the nanostar is therefore proposed from the analysis of the particle dimensions, the aspect ratio of their protuberances, and the gold crystal size. These spiky nanoparticles would find an application as conductive filler in polymeric piezoresistive composites, based on a tunneling conduction mechanism.

Piezoresistive polymer composites based on EPDM and MWNTs for strain sensing applications

AbstractElastomeric composites based on Ethylene-Propylene-Diene-Monomer (EPDM) filled with multi-wall carbon nanotubes (MWNTs) have been prepared, showing improved mechanical properties as compared to the pure EPDM matrix. The results have been discussed using the Guth model. The main focus of the study was on the electrical behavior of these conductive polymer composites (CPCs), in view of possible sensor applications. A linear relation has been found between conductivity and deformations up to 10% strain, which means that such materials could be used for applications such as strain or pressure sensors. Cyclic experiments were conducted to establish whether the linear relation was reversible, which is an important requirement for sensor materials.

Poly(3-hexylthiophene) wrapped carbon nanotube/poly(dimethylsiloxane) composites for use in finger-sensing piezoresistive pressure sensors

We fabricated a piezoresistive composite using multi-walled carbon nanotubes (MWCNTs) as a conductive filler and polydimethylsiloxane (PDMS) as a polymer matrix, which operated in the extremely small pressure range required for finger-sensing. To achieve a homogeneous dispersion of MWCNTs in PDMS, the MWCNTs were modified by a polymer wrapping method using poly(3-hexylthiophene) (P3HT). The percolation threshold of the composites was significantly lowered by the presence of P3HT. The electrical conductivity and piezoresistive sensitivity of the composite were found to strongly depend on the P3HT concentration. The well-dispersed P3HT-MWCNT/PDMS composite showed good piezoresistive characteristics in the 0–0.12 MPa pressure range.

Creep of electrical resistance under uniaxial pressures for carbon black–silicone rubber composite

A composite comprised of dispersed conductive particles in an insulating polymer matrix is an excellent sensing material and could be used in flexible pressure sensors and tactile sensors. In this study, we investigated the variation of electrical resistance as a function of pressure for carbon black–silicone rubber composite. Samples were fabricated with different carbon black volume fractions. From experimental results, it was found that the composite has not only piezoresistivity but also electrical resistance creep behavior, which illustrates the relationship between electrical resistance and time. To describe and predict the above two phenomena, a mathematical model was established for particles filled polymer composites. When the piezoresistive composite was applied as a pressure-sensing unit, errors were seen due to “resistance creep” behavior. Based on this study, a method to inhibit such errors were investigated, developed, and realized.

Piezoresistive TiB 2/silicone rubber composites for circuit breakers

Piezoresistive composites with high hardness and conductivity are required for circuit breakers for multi-cycle operation under large current flow. Based on the simulation results for the mechanical behavior of piezoresistive composites, we developed piezoresistive composites with conductive TiB 2 ceramic materials and silicone rubber. TiB 2 up to 70 vol.% was embedded into the polymer matrix without any mechanical deterioration while the electrical resistance was decreased with increasing TiB 2 content. Piezoresistive composites with 70 vol.% TiB 2 particles exhibited a resistance of 1.7 Ω at a pressure of 1.1 MPa. A circuit breaker with the fabricated piezoresistive composites acted as a switch with a response time of around 2 ms.

Polyesterimide composites as a sensor material for sliding bearings

The piezoresistive polyesterimide composites, with high wear resistance and low friction coefficient were developed and described in this paper. The composites were used in mechanical systems as a bearing material, deposited on the surface of sliding bearing and as a sensor, which can monitor of bearing condition. Composites consist of polyesterimide matrix, electrical conductor powders and lubricating additives. A short review of the background for understanding the electrical transport in such materials is given. A theoretical model for calculation of tribological system resistance has been derived. The results of experiments exhibit good sliding properties and high wear resistance of the composites and a unique feature, i.e. electrical resistivity of bearing material depends on the applied load and temperature. By comparing theoretical calculations with experimental measurements it has been shown that the model for diagnostic system can predict the system resistance with reasonable accuracy.

Micromechanics modeling of smart composites

This paper discusses a summary of analytical modeling as applied to selected smart composites which include piezoelectric composites, shape memory alloy (SMA) fiber composites, and piezoresistive composites. First we discuss the definition of `smart materials' which exhibit coupling among mechanical, thermal and electromagnetic behavior, then the Eshelby's formulations based on a simple algebraic method for predictions of two types of smart composite properties are stated; piezoelectric and SMA composites, followed by the percolation model which is applied to obtain the strain–electric conductivity relations of elastomer composites. The predictions based on these models are shown to be in good agreement with limited experimental results.

Modeling of Piezoresistively-Controlled Electromechanical Smart Material

A finite element model of a proposed smart material was developed. This is an initial investigation into using a piezoresistive sensor in conjunction with a multilayer ceramic actuator and a resistor network as the control circuit. A device model, incorporating piezoresistive composites (with orders of magnitude change in resistivity) and piezoelectric actuators has also been constructed. The model accounts for all relevant material properties and configurations. The software also provides a method of optimizing geometry to obtain desired response. At present the 2-D case predicts a material package with a controllable compliance. This can be extended to a 3-D case consistent with available components.

Recent applications of polyimide to micromachining technology

In this paper, applications of polyimide materials to micromachining technology are reviewed. First, the use of polyimide-based materials as sensor materials are discussed. In this case, the polyimide material is used as an integral part of the micromachined devices. Emphasis is given to the development and characterization of a piezoresistive composite of polyimide and graphite particles. The composite material is characterized for the mechanical properties (Young's modulus, residual stress) and the electromechanical property (piezoresistive coefficient). Second, the use of both photosensitive and nonphotosensitive polyimides as electroplating molds for the fabrication of thick and high aspect ratio metallic microstructures is presented. Extensions of the basic micromolding process, which enable the fabrication of controlled gaps between metallic microstructural components and higher aspect ratio microstructures, are presented. Electroplated metallic microstructures realized using these technologies are shown. In addition, various applications of the polyimide micromolding technologies are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>