Bundle binding in polyelectrolyte solutions

Stiff polyelectrolytes are found to spontaneously form oriented bundles. Conditions under which bundling occurs are found. Molecular dynamics simulations show that divalent counterions are necessary, and the chains must be sufficiently long and stiff. No aggregation occurs for monovalent counterions. For flexible or short chains, aggregation occurs but bundle formation does not. Because of dynamical constraints, the systems tend to order into a network of connected bundles, not a single bundle. [S0031-9007(98)08120-4].