Mehvari Saeid, Sanchez-Vicente Yolanda, González Sergio, Lafdi Khalid
Department of Mechanical & Construction Engineering, Faculty of Engineering & Environment, Northumbria University Newcastle, Newcastle upon Tyne NE1 8ST, UK.
Polymers (Basel). 2022 Mar 23;14(7):1287. 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.
在本研究中，采用溶液混合法和旋涂技术将微米级铜颗粒（小于25μm）掺入聚氨酯（PU）中，以制备浓度为0.5至20体积%的复合薄膜。对这些复合材料在压力下的导电行为进行了实验和数值研究。在压力下进行了面内和面厚度方向的电导率测量。结果发现，在1至20kPa的外加压力下，电导率仅在z方向发生变化。结果表明，对于铜浓度高于2.6体积%的复合材料，压力可诱导电导率高达约7.2×10 S∙m。施加的压力似乎减小了聚合物薄膜的厚度，缩短了铜颗粒之间的距离，促进了导电网络的形成，从而使材料具有导电性。使用一个能够准确提供渗流阈值（PT）浓度的半解析模型来拟合实验电导率。PU-Cu复合材料的PT浓度范围为7.1体积%至1.4体积%，并随压力升高而降低。这被称为压力诱导渗流转变现象（PIPT）。最后，基于代表性体积单元模型（FE-RVE）模拟技术的有限元方法被用于预测导电行为。该数值模拟很好地描述了PT之后的实验电导率，并正确预测了PT浓度。本研究表明，FE-RVE可用于有效模拟压力对聚合物-金属复合材料电学性能的影响，减少了对昂贵且耗时实验的需求。
