Effects of Graphene Reinforcements on the Mechanical and Electrical Properties of PDMS Printed by Inkjet-Based Additive Manufacturing

Abstract Polydimethylsiloxane (PDMS), a versatile silicon-based polymer, is widely used in biomedical devices, microfluidic systems, wearable technology, and electronics due to its mechanical flexibility, optical clarity, electrical conductivity, and biocompatibility. However, its low Young's modulus and tensile strength limit its application in high-stress environments. To enhance its mechanical and functional properties, this study explores the incorporation of graphene (Gr) as reinforcements into the PDMS matrix with a goal of enhancing its mechanical and electrical properties. Despite the potential benefits of Gr, challenges such as aggregation, void formation, and poor interfacial bonding often compromise composites' performance. The study evaluates the effects of Gr reinforcements on the mechanical, microstructural, and dynamic properties as well as electrical resistance of PDMS composites. In this study, graphene-reinforced PDMS composites with different graphene contents (1.5 wt. %, 1.75 wt. %, and 2 wt. %) were printed using direct ink writing (DIW)-based additive manufacturing. To understand the microstructure of the Gr-PDMS composites, we analyzed the microstructure of printed materials using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The experimental results demonstrate that 1.75 wt. % Gr-PDMS achieved an optimal balance between graphene dispersion and aggregation, leading to improved stiffness, as indicated by a 56.6% increase in Young's modulus, though at the expense of a 15.6% decrease in tensile strength and reduced elongation compared to pure PDMS. These findings highlight the tradeoffs between stiffness and ductility in Gr-PDMS. Furthermore, gold-coated 2 wt. % Gr-PDMS exhibited the lowest resistance and highest signal repeatability compared to uncoated Gr-PDMS composites, making it particularly suitable for applications in wearable devices.