MoS2 actuators: reversible mechanical responses of MoS2-polymer nanocomposites to photons.

New molybdenum disulfide (MoS2)-based polymer composites and their reversible mechanical responses to light are presented, suggesting MoS2 as an excellent candidate for energy conversion. Homogeneous mixtures of MoS2/polydimethylsiloxane (PDMS) nanocomposites (0.1-5 wt.%) were prepared and their near infrared (NIR) mechanical responses studied with increasing pre-strains. NIR triggering resulted in an extraordinary change in stress levels of the actuators by ~490 times. Actuation responses of MoS2 polymer composites depended on applied pre-strains. At lower levels of pre-strains (3-9%) the actuators showed reversible expansion while at high levels (15-50%), the actuators exhibited reversible contraction. An opto-mechanical conversion (η)∼0.5-3 MPa W(-1) was calculated. The ratio of maximum stress due to photo-actuation (σmax) at 50% strain to the minimum stress due to photo-actuation (σmin) at 3% strain was found to be ∼315-322% for MoS2 actuators (for 0.1 to 5 wt.% additive), greater than single layer graphene (∼188%) and multi-wall nanotube (∼172%) photo-mechanical actuators. Unlike other photomechanical actuators, the MoS2 actuators exhibited strong light-matter interactions and an unambiguous increase in amplitude of photomechanical response with increasing strains. A power law dependence of σmax/σmin on strains with a scaling exponent of β = 0.87-1.32 was observed, suggesting that the origin of photomechanical response is intertwined dynamically with the molecular mechanisms at play in MoS2 actuators.