Conductivity Behaviour under Pressure of Copper Micro-Additive/Polyurethane Composites (Experimental and Modelling)

• Published in: Polymers 2022-03, Vol.14 (7), p.1287
• Main Authors: Mehvari, Saeid, Sanchez-Vicente, Yolanda, González, Sergio, Lafdi, Khalid
• Format: Article
• Language: English
• Subjects: Carbon fibers; Composite materials; Computer simulation; Copper; Electric properties; Electrical properties; Epoxy resins; Finite element method; Low density polyethylenes; Mathematical models; Nanomaterials; Nanoparticles; Nanowires; Numerical analysis; Particle size; Percolation; Polyethylene; Polymer films; Polymerization; Polymers; Polyurethane resins; Polyurethanes; Silver; Simulation; Spin coating; Thickness
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym14071287

In this study, micro-size copper particles (less than 25 μm) were incorporated into polyurethane (PU) using a solution mixing method and spin-coating technique to fabricate composite films in concentrations from 0.5 to 20 vol.%. The conductivity behaviour of these composites under pressure was studied experimentally and numerically. The conductivity measurements were performed in-plane and through-thickness under pressure. It was found that changes in conductivity only occurred in the z-direction under an applied pressure from 1 to 20 kPa. The results showed that pressure could induce conductivity up to about 7.2 × 10 S∙m for composites with a Cu concentration higher than 2.6 vol.%. It seems that applied pressure reduced the thickness of the polymer film, decreasing the distance between copper particles and promoting the formation of a conductive network, thus making the material conductive. A semi-analytical model that can accurately provide the percolation threshold (PT) concentration was used to fit the experimental conductivity. The PT concentrations for PU-Cu composite ranged from 7.1 vol.% to 1.4 vol.% and decreased with the rise in pressure. This is known as a pressure-induced percolation transition phenomenon (PIPT). Finally, the finite element method based on the representative volume element model (FE-RVE) simulation technique was used to predict the conductivity behaviour. This numerical simulation provided a good description of the experimental conductivity after the PT and correctly predicted the PT concentration. This study shows that FE-RVE could be used to effectively simulate the influence of pressure on the electrical properties of a polymer-metal composite, reducing the need for costly and time-consuming experiments.