Session: 01-02 Sensor and Actuator Materials 1

Paper Number: 167651

167651 - Graphene Nanoplatelet Based Pressure Sensors With Tunable Density and Electrical Conductivity via Foam Compression Molding of Expandable Microspheres 

Piezoresistive sensors with high sensitivity, a broad operating range, and versatile functionalities are in high demand for modern wearable electronics, robotics, and aerospace applications. Electrically conductive porous composites, e.g., conductive composite foams provide light weight and the capability to sense small forces. Existing fabrication methods for lightweight piezoresistive pressure sensors, such as freeze-drying, 3D printing, templating, and gas foaming, are often complex or time-consuming, hindering commercialization and practical applications. This study explores a facile and scalable approach to fabricating functional porous composites for pressure sensing applications via developing segregated structures. The composite foams were made using thermally expandable microspheres (TEMs) and graphene nanoplatelets (GNP) in a compression molding process. In this approach, the TEM powder was first dispersed in water and mixed with a desired amount of GNP aqueous suspension by mechanical stirring for 5 minutes. The TEM/GNP aqueous mixture was poured into a mold and dried at 70 ℃, with a drying time depending on the GNP content. Afterwards, the dried TEM/GNP composite was poured into a mold and compression molded at 150 ℃ for 90 seconds, followed by 4 minutes of cooling under pressure until reaching 70 ℃ to ensure solidified foam formation. Through systematic optimization, ultralightweight foams were fabricated with robust mechanical integrity, a broad density range (0.010–0.200 g/cm³), tunable electrical conductivity (9×10⁻¹³–1×10⁻² S/cm), and excellent compressibility and recovery. The TEM/GNP foams enabled efficient sensor fabrication as well as lower percolation threshold through a segregated structure approach. The TEM/GNP foam containing 1.5 vol.% graphene nanoplatelets with a density of 0.049 g/cm³ and electrical conductivity of 2×10⁻⁵ S/cm was chosen for further mechanical and electromechanical evaluation and investigation of its pressure sensing capabilities. This composite foam demonstrated over a decade of resistance variation (3956–110 Ω) under recoverable strains up to 90% while maintaining strain rate independency in the range of 1–100 mm/min of displacement rate under compression loading. It also exhibited excellent reversibility and reproducibility in piezoresistivity behavior over a thousand compression-release cycles. The gage factor (GF) of the composite foam was chosen to quantify piezoresistive behavior. Under strains up to about 15%, the GF was calculated to be 5.97 with good linearity. Moreover, the TEM/GNP lightweight pressure sensors effectively detected human motions, including touching, walking, arm bending, and finger bending. TEM-based foam sensors offer a simple, low-cost, and scalable process with tunable density, excellent reversibility, and versatility, making them a strong alternative to conventional sensors.

Presenting Author: Amir Ameli UMass Lowell

Presenting Author Biography: Amir Ameli is an Associate Professor of Plastics Engineering at UMass Lowell. He received his PhD from the University of Toronto, Canada. His research interests encompass material design and advanced manufacturing of functional polymeric systems and sustainable materials. His research has been funded by NSF, USDA, DOD, DOE and private sectors. He has published 70+ journal articles and 120+ conference papers.