Electrical Conductivity of Carbon Black - Silicon Rubber Nanocomposites: Effects of Strain, Load and Loading Rate

Background: Carbon black - silicon rubber nanocomposites are under consideration for medical applications involving tremor mitigation as well as general therapeutic applications involving muscle relaxation therapy. Method: Carbon black filled silicon rubber composites containing 40-100 phr (per hundred) carbon black were investigated for their electrical conductivity under different loads over time. Rheological experiments involving evaluations of the storage moduli, G´ for the composites were also performed to infer rate and strain dependence of the composites’ conductivity under compressive loads. Results: Due to the high deformability of silicon rubber, the percolation thresholds for carbon black - silicon composites were shown to be a function of compressive loads applied on them. Conductivity of such composites increased with time and compressive load levels applied. The rheological experiments revealed that strain level and frequency can also indirectly affect the resistivity/conductivity levels in carbon black -filled silicon rubber composites, with the storage modulus increasing monotonically with increasing frequency (rate), and the stiffness of the carbon black /silicon rubber composite decreasing with increasing strain levels. Thus, it becomes easier to compact the nanocomposite further at higher strain levels and we would expect the rate of decay in resistivity to be lower at higher rates of pressure application. Conclusion: Our experimental results reveal that the two important service parameters, strain level and loading rate can be used for controlling the resistivity/conductivity levels in carbon black-filled silicon rubber composites.