Bundle binding in polyelectrolyte solutions

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