Anisotropic Reversible Piezoresistivity in Magnetic-Metallic/Polymer Structured Elastomer Composites: Modelling and Experiments

MIETTA, J.L.; TAMBORENEA, PABLO; NEGRI RICARDO MARTÍN

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 12 p. 422 - 431

1744-683X

In the present article a model accounting for piezoresistivity effects observed instructured filler-polymer elastomer composites is presented. This is a topic of centralrelevance for understanding how conductivity is induced in structured systems,where fillers are aligned forming elongated structures in a preferential orientation.This structure is generated by the application of external forces (magnetic fieldswhen using magnetic fillers) during preparation of the composite. In particular, theanalysis of several variables (angular dispersion of the structures, Young´s modulusof the polymer, fillers and structures density) is of high importance when designinganisotropic stress sensors, because conditions can induce a high enough anisotropyto obtain conductivity and sensing response in only one defined direction. Thesefeatures are not systematically studied in scientific literature and represent a topicthat combines theory and experimental developments. In particular, the conditionsfor obtaining system with total electrical anisotropy are also investigated in thiswork by Monte Carlo simulations of stick percolating objects.The model predictions are compared with experimental results obtained for systemsformed by dispersions in PDMS of microparticle clusters of magnetite-silver, whichare cured in the presence of a uniform magnetic field. Note that fillers aresimultaneously magnetic and electrical conductors. This methodology generateschains of inorganic material inside the polymer, which are preferentially aligned inthe direction of the magnetic field. If now a stress is applied on the cured material(in the preferential direction) then electrical conductivity increases. Thepiezoresistivity properties of that system are modeled here taking into account theseveral factors involved and then contrasted versus experimental results. Simulationsshowing the effects of different model parameters are presented. For these reasons,we consider that Soft Matter is the most appropriated Journal for presenting ourresults.