A new class of nanoengines based on thermoresponsive polymers: Conceptual design and behavior study

A model nanoengine based on endgrafted Poly(N-isopropylacrylamide) (PNIPAM) on graphene-like sheets is proposed. The nanoengine consists of a water-filled slab and four PNIPAM chains, which are at one end grafted to one of the slab walls and on the other end to a mobile square graphene ‘piston’. The basis of the reciprocating motion of the piston is the reversible coil-to-globule transition of polymer chains when changing the temperature of the aqueous environment. Molecular dynamics simulations have been used to investigate the behavior of the proposed system at the full atomistic level. At temperatures below the lower critical solution temperature (LCST) PNIPAM chains are swollen and the nanopiston is in an expanded open state. Above the LCST, the PNIPAM chains are shrunken and the piston is retracted. The studied nanopiston exhibits an amplitude of approximately 10 Å when the temperature is reduced from 310 to 300 K or increased from 300 to 310 K with a frequency of about 109 rotations per minute; however the efficiency is very low.