  The de Gennes' blob model is extensively used in different problems of
polymer physics. This model is theoretically applicable when the number of
monomers inside each blob is large enough. For confined flexible polymers, this
requires the confining geometry to be much larger than the monomer size. In
this manuscript, the opposite limit of polymer in nano-slits with one to
several monomers width is studied, using molecular dynamics simulations.
Extension of the polymer inside nanoslits, confinement force on the plates, and
the effective spring constant of the confined polymer are investigated. Despite
of the theoretical limitations of the blob model, the simulation results are
explained with the blob model very well. The agreement is observed for the
static properties and the dynamic spring constant of the polymer. A theoretical
description of the conditions under which the dynamic spring constant of the
polymer is independent of the small number of monomers inside blobs is given.
Our results on the limit of applicability of the blob model can be useful in
the design of nanotechnology devices.
