Sensitive electromechanical sensors using viscoelastic graphene polymer nanocomposites
Super sensitive, not so silly, putty Many composites blend stiff materials, such as glass or carbon fibers, into a softer elastic polymer matrix to generate a material with better overall mechanical toughness. Boland et al. added graphene to a lightly cross linked silicone polymer (also known as Silly Putty) The resulting composite has unusual mechanical properties, allowing the manufacture of strain sensors that can detect respiration and the footsteps of spiders. Science, this issue p. 1257 A composite of graphene and a viscoelastic polymer results in a material with unexpected electromechanical properties. Despite its widespread use in nanocomposites, the effect of embedding graphene in highly viscoelastic polymer matrices is not well understood. We added graphene to a lightly cross linked polysilicone, often encountered as Silly Putty, changing its electromechanical properties substantially. The resulting nanocomposites display unusual electromechanical behavior, such as postdeformation temporal relaxation of electrical resistance and nonmonotonic changes in resistivity with strain. These phenomena are associated with the mobility of the nanosheets in the low viscosity polymer matrix. By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties. These nanocomposites are sensitive electromechanical sensors with gauge factors >500 that can measure pulse, blood pressure, and even the impact associated with the footsteps of a small spider.
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