Facile one-step preparation of laminated PDMS based flexible strain sensors with high conductivity and sensitivity via filler sedimentation

Abstract Rubber based conductive composites with laminated structures are promising approaches to prepare flexible sensors with high performance abilities. Herein we report a facile one-step method to prepare polydimethylsiloxane (PDMS) based flexible strain sensors with a laminated structure via filler sedimentation. Nickel coated graphite (NCG) conductive fillers were homogenosly dispersed into a PDMS solution and then allowed to form a sedimention layer by allowing the mixture to stand for 2 h to obtain composite sensors. PDMS/NCG composites presented a two dimensional conductive network with a low percolation value of 2.52 vol% and high conductivity of 148 S/m at 11.11 vol% NCG. Due to the laminated structure, the Younge's modulus of the composites increased from 0.88 MPa for pure PDMS to only 1.98 MPa for 11.11 vol% NCG indicating high flexibility. Under applied stress, composite resistances increased from 8 to 20 Ω (varied by vol% NCG) to 4 × 108 Ω and presented a gauge factor (GF) of 5.6 × 108, amongst the highest values when compared with published results. Composite resistance under strain is explained by constriction, tunneling, and hopping mechanisms, and experimental results agree well with theoretical values. Filler sedimentation is demonstrated to be a valuable method to produce highly conductive and sensitive rubber based, laminated flexible sensors requiring only one preparation step.