We investigate the concept of molecular-sized outward-swinging gate. Our theoretical analysis, Monte Carlo simulation, and direct solution of the governing equations all suggest that across such a gate, under the condition of local nonchaoticity, the probabilities of particle crossing are unequal in the two directions. It was confirmed by an experiment using a nanoporous membrane one-sidedly surface-grafted with bendable organic chains. Remarkably, through the membrane, gas spontaneously and repeatedly flew from the low-pressure side to the high-pressure side, clearly demonstrating an asymmetric gas permeability. We show that while this phenomenon is counterintuitive, it follows the basic principle of thermodynamics, as entropy remains maximized. What makes the system unique is that the locally nonchaotic gate interrupts the probability distribution of the local microstates, and imposes additional constraints on the global microstates, so that entropy reaches a nonequilibrium maximum. Such a mechanism is fundamentally different from Maxwells demon, and is consistent with microscopic reversibility. When the local nonchaoticity is lost, the gate would converge to the classical systems, such as Smoluchowskis trapdoor and Feynmans rachet.
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