Collapse transitions of a supersized neutral chain due to irreversibly adsorbed small colloidal particles |
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Authors: | P Chodanowski S Stoll |
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Institution: | (1) Analytical and Biophysical Environmental Chemistry (CABE) Department of Inorganic Analytical and Applied Chemistry University of Geneva, Sciences II 30 quai E. Ansermet, CH – 1211 Geneva 4, Switzerland e-mail: serge.stoll@cabe.unige.ch, CH |
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Abstract: | We performed Monte Carlo simulations to study the destabilization processes of large neutral and flexible polymer chains
due to irreversibly adsorbed colloidal particles attached to the chains like beads on a necklace. The particles are modeled
as charged spherical units which interact with each other via repulsive electrostatic and attractive van der Waals (vdW) potentials.
The usual Monte Carlo search procedure is extended and carefully checked to completely sample the chain conformational space
and achieve dense conformations in the limit of both strong attractive and repulsive interaction potentials. Configurational
properties, such as the radius of gyration, the end-to-end length, and the Kuhn length, are calculated as a function of the
intensity of the vdW interactions and ionic strength values. It is observed that chains exhibit a new range of possible conformations
compared to the classical random walk and self avoiding walk chains or polyelectrolytes. In the limit of low salt concentration,
by gradually increasing vdW interactions, chains undergo a cascade of transitions from extended structures to dumbbells, from
dumbbells to pearl necklaces, and from pearl necklaces to collapsed coils. Because of strong competition between the vdW and
electrostatic forces, the distance along the chain between the interacting particles, and the sampling limitations, these
transitions are found to sample metastable domains and to depend on the initial conformations. To gain insight into the spatial
organization of the collapsed conformations, the pair correlation functions of both monomers and particles are calculated.
It is shown that collapsed conformations which are the result of strong particle–particle interactions exhibit two distinct
parts: a hard core mainly composed of particles and a surrounding polymeric shell composed of loops and tails. Possible effects
of such a collapsed transition on the kinetics of flocculation of a mixture containing large flexible chains and small adsorbing
colloidal particles are discussed.
Received: 26 July 1999 Accepted in revised form: 9 November 1999 |
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Keywords: | Polymer conformation Adsorbed colloidal particles Monte Carlo simulations Collapse transition |
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