Mechanisms of Cooperation and Competition of two Species Transport in Narrow Nanochannels

Abstract: Flow of particles of two different species through a narrow channel with solely two discrete spatial positions is analyzed with respect to the species' capability to cooperate or compete for transport. In contrast to mean field approaches, spatial correlations are explicitly conserved. A strong repulsive interaction between particles of the same kind and a very attractive channel imply a strong entanglement of transport of both species. This is reflected by the magnitude of transition flows in state space which in the extreme case of perfect coupling are restricted to a cyclic sub space. Entanglement of transport implies that the species mutually exert entropic forces on each other. For parallel directed concentration gradients this implies that the species' ability to cooperate increases with the degree of entanglement. Thus, the gradient of one species reciprocally induce a higher flow of the other species when compared to that in its absence. The opposite holds for antiparallel gradients where species mutually hamper their transport. For a sufficient strong coupling, the species under the influence of the stronger concentration gradient drives the other against its gradient, i.e. flow and gradient of the driven species become antiparallel. Hence, besides the positive entropy production generated by the driving species a negative component of entropy production of the driven species emerges. The sources of both, positive and negative entropy production, can be localized in state space. The stronger the coupling of transport the higher is the degree of efficiency, i.e. the amount of negative entropy production on cost of the positive one.