The dynamics of the detachment of single polyethylene (PE) chains from a strong adsorption surface is investigated by the steered molecular dynamics method (SMD).Our simulations use the unitedatom (UA) model of PE chains

which regards each CH2 and CH group as a monomer.Due to the significant reduction of the number of the degrees of freedom

the UA model allows one to explore longer chains or a larger number of systems within the limited computational time.In the previous investigations with SMD

the simulation is performed only once

and the statistical properties can not be discussed.In this work

the statistical behavior of single PE chains pulled from the strong adsorption surface is investigated with the SMD and MC method.There exists a long force plateau for the curve of average force probed by spring f

which agrees well with the experimental results.The relationship between the average forcef and the pulling velocity v shows two distinctive regions:a weak dependence region as v0.001 nm/ps

and a strong dependence region as v0.001 nm/ps. Remarkably

the PE chain manifests force hysteresis under sequential stretching and releasing.The area of the hysteresis also increases with the velocity v. Force-extension curves display hysteresis because the velocity at which the polymer chain is stretched and released exceeds the velocity of unfolding and folding of the polymer at equilibrium at that extension.If the stretchingreleasing had been done at a very low velocity used in the experiment

the stretching or releasing curves will converge toward a single intermediate curve representing the equilibrium process.Some results in our simulation agree well with the available experimental results

while the others may provide some insights into the related processes and further experimental investigatiozns.