"The idea came from playing in the lab. My student, Conor Boland, thought it would be interesting to mix graphene with the x-linked polymer that makes up silly putty. It was! It turned out that the very soft matrix resulted in quite interesting properties. This started a 30 month research program" told Prof. Coleman in a telephone interview with EE Times Europe.
The resulting paper "Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites" published in the Science journal details how mixing graphene nanosheets to highly viscoelastic polysilicone matrices (also commercialized as children's play material silly putty) gave rise to unusual electromechanical properties that could be exploited to manufacture ultra-sensitive strain sensors.
What the researchers have shown with their homemade "G-putty" as they call it, is that the dense uniform and isotropic network of graphene nanosheets formed within the low viscosity cross-linked polymer not only drastically increased the electrical conductivity of the compound (reaching about 0.1 S/m at a 15 volume %) but also remained highly mobile and compliant.
This high mobility of the graphene nanosheets means that as a small tensile strain step is applied to the G-putty, a sharp increase in electrical resistance is observed before decaying slowly as the network of graphene nanosheets slowly relaxes, reforming connections and giving a resistance decrease. The researchers were able to develop a quantitative model to describe accurately that post-deformation temporal relaxation of the electrical resistance and the non-monotonic changes in resistivity with strain.
"This network relaxation can be thought of as a self-healing process. Such filler mobility is unprecedented in nanocomposites at room temperature. However, it also represents plasticity, meaning deformations are not fully reversible" the researchers wrote in their paper.