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Aggregation of interacting polyelectrolytes and sequence and conformations of polyampholytes

Devesh Srivastava, University of Massachusetts Amherst


The structure of aggregates formed by oppositely charged polyelectrolytes of the same chain length N and charge density and the kinetics of the formation of these aggregates has been studied using a dynamic Monte Carlo algorithm. The model considers the evolution of chains through local motion of monomers and exhibits the complex behavior associated with the formation of such aggregates. The chains interpenetrate in two distinct steps--the chains first diffuse towards each other and then collapse abruptly to form smaller aggregates. This abrupt collapse is a consequence of cooperativity in the aggregation process. The chains collapse and are considerably smaller in the aggregate than in isolation; the conformational properties of each of the two chains of the same chain length and charge density in the aggregate are the same. The radii of gyration of the chains in the aggregate and of the aggregate scale as $N\sp{1/2}$. Aggregates formed by longer chains initially scale as N. These aggregates continue to reorganize and eventually scale as $N\sp{1/2}$. However, it is possible that for sufficiently long chains, as in real experimental situations, this process of reorganization is hindered by the formation of entanglements etc. The aggregates would then form a non-equilibrium structure and would not scale as $N\sp{1/2}$. The conformation of randomly but specifically sequenced polyampholytes are determined by the interplay of the polyelectrolyte effect and the polyampholyte effect. The relative importance of the two is determined by the location of charges along the chain. Polyampholytes adopt extended conformations like self avoiding walk at high temperatures and collapsed structures at low temperatures. This difference arises from differences in the location of charges along the chain. Differences in the location of charges along the chain also lead to differences in the conformational spectrum and in the energy spectrum of the polyampholytes.

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Recommended Citation

Srivastava, Devesh, "Aggregation of interacting polyelectrolytes and sequence and conformations of polyampholytes" (1997). Doctoral Dissertations Available from Proquest. AAI9737587.