  Free energy barrier for entry of a charged polymer into a nanoscale channel
by a driving electric field is studied theoretically and using molecular
dynamics simulations. Dependence of the barrier height on the polymer length,
the driving field strength, and the channel entrance geometry is investigated.
Squeezing effect of the electric field on the polymer before its entry to the
channel is taken into account. It is shown that lateral confinement of the
polymer prior to its entry changes the polymer length dependence of the barrier
height noticeably. Our theory and simulation results are in good agreement and
reasonably describe related experimental data.
