Three-dimensional free-standing heterostructures out of MoS₂ and rGO with infused PDMS towards electromechanical pressure sensing

The behavior of two-dimensional (2D) materials constructed as three-dimensional structures is studied to bring such materials one step closer to the real-life application. Lattices structures of gyroid triply periodic minimal surface (TPMS) were fabricated out of 2D materials, namely, molybdenum disulfide (MoS₂), and reduced graphene oxide (rGO), forming for the first time free-standing MoS₂ (FSM) lattice and free-standing hetero-structural lattice of MoS₂ and rGO (FSH) out of TPMS. These 2D materials were also integrated with polydimethylsiloxane (PDMS) elastomer, forming FSM/PDMS and FSH/PDMS composites. Mechanical characterization, including compression and cyclic tests, were conducted on FSM, FSH, and the composites. Additionally, electromechanical characterization was conducted to evaluate the sensing potential of these structures. It is worth noting that the elastic modulus of the 10 unit-cells with either FSM or FSH was higher than the other lattices of the same type. FSH tends to have a higher modulus at 1504.4 kPa in the 10 unit-cells. This modulus is even higher at 3 MPa when PDMS is added to the FSH lattice. Due to the brittle fracture, FSM or FSH lattices follow the layer-by-layer failure mechanism. Samples with PDMS are more stable towards such cyclic tests without noticeable failures or a decrease in elastic modulus. Finally, the 10 unit-cell lattices of FSH/PDMS composite have the highest conductivity at 2.5 mA, and a comparable sensitivity at 0.365 kPa⁻¹ over the range of 0-100 kPa.