Grafted polymers with annealed excluded volume: A model for surfactant association in brushes |
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Authors: | EPK Currie GJ Fleer MA Cohen Stuart OV Borisov |
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Institution: | (1) University of Wageningen, Department of Physical and Colloid Chemistry, 6703 HB Wageningen, The Netherlands, NL;(2) Institute of Macromolecular Compounds of the Russian Academy of Sciences, 199004, St. Petersburg, Russia, RU |
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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.
Received 26 November 1998 and Received in final form 2 April 1999 |
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Keywords: | PACS 36 20 Ey Conformation (statistics and dynamics) - 61 25 Hq Macromolecular and polymer solutions polymer melts swelling - 82 70 Dd Colloids |
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