Eur. Phys. J. E 1, 27-40
Grafted polymers with annealed excluded
volume:
A model for surfactant association in brushes
E.P.K. Currie1 - G.J. Fleer1 - M.A. Cohen Stuart1 - O.V. Borisov1,2
1 University of Wageningen,
Department of Physical and
Colloid
Chemistry,
6703 HB Wageningen, The Netherlands
2 Institute
of
Macromolecular Compounds of
the Russian Academy of Sciences,
199004,
St. Petersburg, Russia
borisov@zx.basf-ag.de
Received 26 November 1998 and Received in final form 2 April 1999
Abstract
We
present an analytical self-consistent-field (SCF) theory for a
neutral
polymer brush (a
layer of
long polymer chains end-grafted to a
surface)
with annealed
excluded volume interactions between the monomer
units.
This model mimics the reversible adsorption of solute
molecules
or
aggregates, such as small globular proteins or
surfactant
micelles, on the grafted chains.
The
equilibrium structural properties of
the brush
(the brush thickness, the
monomer density profile,
the
distribution of the end segments of the grafted chains) as well as
the
overall adsorbed amount
and the adsorbate density profile
are analyzed
as a
function of the grafting density, the excluded volume parameters and
the
chemical
potential (the concentration) of the adsorbate in
the
solution.
We demonstrate that, when the grafting density is varied,
the
overall adsorbed amount
always exhibits a
maximum, whereas
the root-mean-square brush
thickness either
increases
monotonically
or passes through a (local)
minimum.
At high grafting densities
the chains are loaded by adsorbed
aggregates
preferentially
in the
distal region of the brush,
whereas in the
region proximal to
the grafting surface depletion of
aggregates occurs
and
the polymer brush retains an unperturbed structure.
Depending on
the
relative
strength of the excluded volume interactions between
unloaded
and loaded monomers both the degree of loading of the chains
and the
polymer density profile are either
continuous or they exhibit a
discontinuity as a function of the distance
from the
grafting surface.
In
the latter case intrinsic phase separation
occurs in the brush: the dense phase consists of unloaded
and weakly
extended chains and occupies the region proximal to the
surface,
whereas a more
dilute phase consisting of highly loaded and
strongly extended chains
forms the periphery of the
brush.
PACS
36.20.Ey Conformation (statistics and dynamics)
-
61.25.Hq Macromolecular and
polymer solutions; polymer melts; swelling
-
82.70.Dd Colloids
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
