Monte Carlo simulations of probe-host chain entanglement: Influence of host mobility and size on probe electrophoretic motion

A Monte Carlo method simulates chain trajectories during the pairwise confi gurational interactions of a single field-driven polyelectrolyte "probe" ch ain and a single neutral "host" chain. The goal is to understand how the mo bility and chain length of dilute, neutral polymers affect the separation o f dilute polyelectrolytes during capillary electrophoresis in a neutral pol ymer solution. The simulations fix probe charge density, Debye-Huckel scree ning length, and probe-host starting displacement, but vary chain length fr om 50 to 200 and 70 to 200 Kuhn steps, respectively, for flexible probe and hosts. Many trajectories lead to probe-host chain entanglement, an event b elieved responsible for the polyelectrolyte size discrimination observed in actual experiments. Chain distortions in response to such entanglement fre quently produce double hairpin configurations that persist until the shorte st hairpin arm slides past the locus of entanglement. Average probe velocit y exhibits a minimum when probe and host chain lengths are nearly equal. Th e minimum reflects an interplay of two effects: the average duration of ent anglement, which by increasing with probe length reduces mobility, and the average displacement of an entanglement, which by increasing with probe len gth raises mobility.