Stress‐Induced Dielectric Response of Graphene Nanoplatelets Loaded Ultra‐Lightweight, Flexible Polyurethane Foam for Pressure‐Based Sensing Application

This work explores the mechanism of stress‐induced dielectric response of graphene nanoplatelets loaded flexible polyurethane foam for potential sensing applications. The polyurethane foam composite is prepared by premixing graphene with polyether polyol and a blowing agent, followed by reaction with isocyanate. The mechanical properties show that the developed foam possesses admirable compressive strength. The bulk density is found to decrease with graphene loading. The wettability studies show the hydrophobic nature of the foam upon graphene loading. Cell morphology divulges information about the polymer matrix and dispersion of nanofillers in it. The thermal behavior of the foam is also noted at different levels of filler loading. The dielectric properties, such as capacitance and electrical conductivity, are studied under compression at varying frequencies and applied stresses, which show a gradient change in properties due to the formation of conductive pathways acting as charge carriers. The behavior of the nanofiller at the lower and higher frequencies reveals the charge transfer mechanism over this variation. The highest capacitance value of approximately 4.8 pF at 100 Hz under the highest applied strain (~80%) and the highest conductivity, 2.5 × 10 −3 μS/m at 80% strain with 5 kHz was recorded at 0.7 wt% graphene loading. Finally, the study gives insight into producing conductive polymeric foam that can be used as a stress sensor for novel applications such as in health care as a wearable sensor connected to the body, monitoring real‐time movement. As the emerging scenario requires a lightweight and heterogeneity, flexible polyurethane foam provides a good solution.