Eur. Phys. J. E 8, 531-537 (2002)
DOI: 10.1140/epje/i2002-10041-1
Polymer depletion interaction between parallel walls -A Monte Carlo study
A. MilchevInstitute for Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria milchev@ipchp.ipc.bas.bg
(Received 16 May 2002 and Received in final form 1 August 2002 Online publication 3 September 2002)
Abstract
An off-lattice bead-spring model of self-assembling equilibrium ("living") polymers is used to study the
polymer-induced interaction between parallel walls immersed in polydisperse solutions of different
concentration by means of Monte Carlo simulation. The two walls form an open slit in contact with an
external reservoir so that the confined system may exchange monomers with the surrounding phase
and adapt its polydispersity in order to relax the confinement constraint. We find that the
properties of the polymers in the constrained system as well as the net force
acting on the walls
depend essentially on the polymer concentration in the reservoir which leads to qualitative
differences in their behavior with changing inter-planar distance
H:
In a dilute polymer solution at concentration
below the semi-dilute threshold
the force between the walls is attractive and decreases steadily with growing wall separation
H, so
that
at
if
H is measured in gyration radii
of the unperturbed
polymers. The total monomer
concentration within the slit is smaller than the concentration in the reservoir and decreases
monotonically with
. The ratio
of mean chain length
in the slit to that in the reservoir,
, decreases from unity at
,
goes through a minimum at
, and then rises again to
for wall
separations
.
In contrast, in a dense solution of equilibrium polymers at
one detects no indirect
wall-wall interaction,
, for
H larger than the monomer size. Thus, earlier
speculations about the existence of possible depletion interaction between parallel walls even
in a dense polymer system cannot be confirmed. Inside the slit the monomer density is found to be
always larger than in the reservoir while
and decreases steadily as
.
The depletion force between parallel plates has been determined also in a monodisperse solution of
conventional polymers. Qualitatively the force behavior does not differ from that of living polymers.
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
07.05.Tp - Computer modeling and simulation.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002