Effect of force and location of bottleneck for particle moving through window under encapsulation

• Published in: Journal of chemical sciences (Bangalore, India) India), 2017-08, Vol.129 (8), p.1293-1300
• Main Authors: Sharma, Anirban, Ghorai, Pradip Kr
• Format: Article
• Language: English
• Subjects: Activation energy; Cancellation; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Diffusion effects; Encapsulation; Particle size; Regular Article
• ISSN: 0974-3626; 0973-7103
• DOI: 10.1007/s12039-017-1336-9

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 parts of 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. Graphical Abstract Correlation between diffusivity ( D ) and activation energy ( E a ) in faujasite zeolite is shown. Force cancellation at the window of microporous material does not play any role in the diffusion process unless diffusing particle size is larger than the window free diameter. The location of bottleneck for diffusion is not at the window, it is always 2.6 Å to 3.0 Å away from the window plane.