This study presents the elasticity of single polyethylene (PE) chains with one end fixed based on the steered molecular dynamics (SMD) method.During the tensile process

we find that the average pulling force 〈f〉 displays a dependence of pulling velocity v When the pulling velocity v 0.05 nm/ps

the average pulling force 〈f〉 increases first and then keeps a plateau of a constant force around 250 pN.The shape factors of the polyethylene (PE) chain are investigated during the pulling process.Here

〈δh〉、〈δm〉 and 〈δt〉 are the shape factors of the head segment

middle segment and the tail segment of the single polyethylene (PE) chain.We find that 〈δh〉 and 〈δt〉 increase obviously in the low extension area

but〈δm〉 keeps unchanged.However

〈δm〉 increases rapidly in the high extension area.We conclude that the shape of the head segment and tail segment of the polyethylene (PE) chain change first

and then the shapes of the middle segment changes during the pulling process.If we sequentially release the stretching chain

the polyethylene (PE) chain exhibits force hysteresis.This means that the stretching and releasing follow different paths.The results agree well with the experimental results of the force hysteresis by Kellermayer et al.The force extension curves display hysteresis because the pulling velocity at which the single polyethylene (PE) chain is stretching and the release exceedal the velocity of molecular thermal fluctuation.The area enclosed by the force hysteresis represents the dissipated energy〈Ed〉

which has a relationship with pulling velocity v.Behavior of 〈Ed〉v can be fitted with a curvilinear equation of〈Ed〉=a+b×e-cv

and shows two distinct cases:a weak dependence as v0005nm/ps

〈Ed〉 almost keeps unchanged with the increase of the pulling velocity v

and a strong dependence as v0.005 nm/ps

〈Ed〉 increases obviously with the pulling velocity v. Furthermore

at different thermodynamics temperature areas of single polyethylene (PE) chain

〈Ed〉 shows different behaviors.At high temperature areas T220 K

〈Ed〉 decreases with the increase of the temperature

which agrees well with the experimental results of energy dissipated in a loading-unloading cycle of poly(butylene terephthalate) by Pegoretti et al. However

the experiment can’t be realized at low temperature.Our computer simulations can overcome the unaccessible condition in real experiments.We find that 〈Ed〉 decreases with the decrease of the temperature at low temperature area T220 K.All these investigations may provide some insights into the elastic behavior of polymer chains.