Opto-electro-mechanical percolative composites from 2D layered materials: Properties and applications in strain sensing

Abstract The fragmentation rate (FR) of two-dimensional layered materials (2DLMs) MoS 2 , WS 2 , and graphene in N- methyl-pyrrolidinone (NMP) was computed, where FR is a measure of the particle size reduction with ultrasonication time. For the 2DLMs, the highest FR generally occurred for sonication times t sonic  = 30 min, with FR Graphite  ∼ −1176.4 μm-hr −1 , FR WS2  ∼ −32.4 μm-hr −1 and FR MoS2  ∼ −3.8 μm-hr −1 . This is in contrast to a non-layered material, Al nanoparticles, where FR Al ∼0 μm-hr −1 for t sonic  = 30 min. Knowledge of the particle size as a function of t sonic has not been reported previously for 2DLMs, and is extremely important as these materials are integrated into additively manufactured platforms, such as ink-jet printing and three-dimensional (3D) printing. The treated materials were then infused with two types of polymers, flexible and stretchable polyisoprene, and an optically transparent acrylic, poly-methyl-methacrylate (PMMA) for opto-electro-mechanical strain-based sensing device applications. In particular, the hybrid composites of graphene with optically transparent and bendable PMMA revealed the potential of forming opto-mechanical filters, where optical filtering can be engineered through the graphene loading. The polyisoprene-graphene composites were piezoresistive with potential for wearable electronics, where mechanical strain, as induced at joint movements on a finger for example, modulates the current with joint displacement. Strain levels of up to 200% were observed and the gauge factor of these devices was measured to be ∼75 which is > 10X higher compared to conventional metal-foil based strain sensors. This work sheds fundamental insights into the role of sonication on the materials properties of 2DLMs in solution dispersions and shows their potential in hybrid composites for opto-electro-mechanical strain based sensing applications and in wearable electronics.