We consider polymers, modelled as self-avoiding chains, confined on a
strip defined on the square lattice with spacing a in the (x, y) plane
, limited by two walls which are impenetrable to the chains and locate
d at x = 0 and x = m. The activity of a monomer incorporated into the
chain is defined as z = exp(beta mu) and each monomer adsorbed on the
wall, that is, located at sites with x = 0 or x = m, contributes with
a Boltzmann factor omega = exp(-beta epsilon) to the partition functio
n. Therefore, epsilon < 0 corresponds to walls which are attractive to
the monomers, while for epsilon > 0 the walls are repulsive. In parti
cular, we calculate the tension between the walls, as a function of m
and omega, for the critical activity z(c), at which the mean number of
monomers diverges (the so called polymerization transition). For omeg
a > 1 --> 1.549375..., the tension on the walls is repulsive for small
values of m, becoming attractive as m is increased and finally becomi
ng repulsive again. As omega is increased, the region of values of m f
or which the tension is attractive grows.