Abstract
AbstractHere, an approach is presented to incorporate graphene nanosheets into a silicone rubber matrix via solid stabilization of oil‐in‐water emulsions. These emulsions can be cured into discrete, graphene‐coated silicone balls or continuous, elastomeric films by controlling the degree of coalescence. The electromechanical properties of the resulting composites as a function of interdiffusion time and graphene loading level are characterized. With conductivities approaching 1 S m−1, elongation to break up to 160%, and a gauge factor of ≈20 in the low‐strain linear regime, small strains such as pulse can be accurately measured. At higher strains, the electromechanical response exhibits a robust exponential dependence, allowing accurate readout for higher strain movements such as chest motion and joint bending. The exponential gauge factor is found to be ≈20, independent of loading level and valid up to 80% strain; this consistent performance is due to the emulsion‐templated microstructure of the composites. The robust behavior may facilitate high‐strain sensing in the nonlinear regime using nanocomposites, where relative resistance change values in excess of 107 enable highly accurate bodily motion monitoring.
Highlights
O'Mara, Marcus A, Ogilvie, Sean P, Large, Matthew J, Salvage, Jonathan P, Graf, Aline Amorim, Sehnal, Anne C, Lynch, Peter J, Salvage, Jonathan P, Jurewicz, Izabela, King, Alice A K and Dalton, Alan B (2020) Ultrasensitive strain gauges enabled by graphene-stabilized silicone emulsions
A high surface energy “water” phase consists of water and ethylene glycol (EG), and a low surface energy “oil” phase contains dichloromethane (DCM), ethyl acetate (EA), and a commercial platinum-cure PDMS elastomer system
The oil phase solvents were identified by adopting a Hansen parameter matching approach; solvents intermediate to graphene and PDMS in Hansen space were identified as possible candidates
Summary
This is consistent with relatively large, defect free graphene sheets,[5] with potentially some influence of residual surfactant We note that this value is somewhat lower than that expected for liquid-exfoliated graphene prepared in solvents such as N-methyl-2-pyrrolidone (NMP) where the surface energy matching is often taken to imply that γgraphene = 71 mN m−1.[5] Equation (1) is plotted as a solid black curve on Figure 1E with the defining value of γgraphene = 66 mN m−1 taken from the above estimate. If we identify the droplet diameter d in Equation (2) with ⟨d⟩ plotted, we see that the functional form ⟨d⟩ ∝ φ−1 is compatible with the data This would suggest that S is constant and no overcoating of the interfaces occurs with additional graphene.
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