Anisotropic reversible piezoresistivity in magnetic–metallic/polymer structured elastomeric composites: modelling and experiments

Abstract

Structured elastomeric composites (SECs) with electrically conductive fillers display anisotropic piezoresistivity. The fillers do not form string-of-particle structures but pseudo-chains formed by grouping micro-sized clusters containing nanomagnetic particles surrounded by noble metals (e.g. silver, Ag). The pseudo-chains are formed when curing or preparing the composite in the presence of a uniform magnetic field, thus pseudo-chains are aligned in the direction of the field. The electrical conduction through pseudo-chains is analyzed and a constitutive model for the anisotropic reversible piezoresistivity in SECs is proposed. Several effects and characteristics, such as electron tunnelling, conduction inside the pseudo-chains, and chain-contact resistivity, are included in the model. Experimental results of electrical resistance, R, as a function of the normal stress applied in the direction of the pseudo-chains, P, are very well fitted by the model in the case of Fe3O4[Ag] microparticles magnetically aligned while curing in polydimethylsiloxane, PDMS. The cross sensitivity of different parameters (like the potential barrier and the effective distance for electron tunnelling) is evaluated. The model predicts the presence of several gaps for electron tunnelling inside the pseudo-chains. Estimates of those parameters for the mentioned experimental system under strains up to 20% are presented. Simulations of the expected response for other systems are performed showing the influence of Young's modulus and other parameters on the predicted piezoresistivity.

Incorporation of Conductive Materials into Hydrogels for Tissue Engineering Applications

“…It is essential that the conductive component achieves homogeneous mixing so that the conductive path is generated in a nonconductive hydrogel network. It is important that the metallic particles incorporated in hydrogels form interconnecting pathways of particles for electron transfer without compromising the physical properties of the hydrogel [127].…”

Mechanisms for Imparting Conductivity to Nonconductive Polymeric Biomaterials

“…Although metal particle inclusions have been investigated for applications such as bone repair and dental restoration [ 172,173 ] there have been relatively few investigations relating to biomedical electrode applications. [ 174 ] A common issue with use of discrete particles in polymer matrices is the capacity to form interconnected pathways for electron transfer at particle concentrations that do not disrupt the polymer Figure 5 . Schematic procedures used to prepare buckled Au or PPy/pTS fi lms on SIBS substrate and FESEM images of these products.…”

“…Metal inclusions such as micro and nanoparticles and wires have been applied as fillers in polymers to enhance electrical properties. Although metal particle inclusions have been investigated for applications such as bone repair and dental restoration there have been relatively few investigations relating to biomedical electrode applications . A common issue with use of discrete particles in polymer matrices is the capacity to form interconnected pathways for electron transfer at particle concentrations that do not disrupt the polymer mechanics.…”

“…A common issue with use of discrete particles in polymer matrices is the capacity to form interconnected pathways for electron transfer at particle concentrations that do not disrupt the polymer mechanics. Mietta et al modeled the behavior of elastomeric composites with metallic particles and suggested that conductivity may rely on individual particles or clusters of particles being connected via metallic ions within the polymer matrix, or what they termed pseudo‐chains. The use of metallic wires, in particular nanowires in composites, has the potential to overcome the interconnectivity problem and thus reduce the amount of metal required to reach the percolation threshold.…”

Incorporation of Conductive Materials into Hydrogels for Tissue Engineering Applications

“…It is important that the metallic particles incorporated in hydrogels form interconnecting pathways of particles for electron transfer without compromising the physical properties of the hydrogel [123]. Although it is difficult for a network of nanowires to control uniform distribution [124][125][126][127][128][129][130], conductive hydrogels with nanowires can be fabricated for a wide range of tissue engineering fields, such as pressure sensors, biosensors, and electrophysiological catheters [131][132][133].…”