One of the central assumptions to explain appearance of an anomalous diffusion regime in microporous materials is the cancellation of forces experienced by a moving particle at the bottleneck. In this work, we examine this issue of force cancellation inside a microporous material exploring the diffusion path and cross-checking bottleneck associated with diffusion. Conventional wisdom is that window of a microporous material is the bottleneck for diffusion. Our study reveals that bottleneck for diffusion is not at the window, it is always 2.6 Å to 3.0 Å away from the window plane and depending on guest size, it lies in different partsof the inner surface of α-cage. Window has significant effect in diffusion process only when diffusing particle size is comparable or larger than the window free diameter. Window does not play any role if particle size is smaller than window free diameter. We show that in the anomalous diffusion regime there is no signature of force cancellation at the window. Activation energy and total force along the diffusion path are responsible for the existence of anomalous diffusion regime in microporous materials.
Volume 134, 2022
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