Scanning of Adsorption Hysteresis In Situ with Small Angle X-Ray Scattering.

Athanasios Ch Mitropoulos,Etienne F Vansant,Konstantinos L Stefanopoulos,Evangelos P Favvas,Warren Batchelor

doi:10.1371/journal.pone.0164636

Abstract

Everett’s theorem-6 of the domain theory was examined by conducting adsorption in situ with small angle x-ray scattering (SAXS) supplemented by the contrast matching technique. The study focuses on the spectrum differences of a point to which the system arrives from different scanning paths. It is noted that according to this theorem at a common point the system has similar macroscopic properties. Furthermore it was examined the memory string of the system. We concluded that opposite to theorem-6: a) at a common point the system can reach in a finite (not an infinite) number of ways, b) a correction for the thickness of the adsorbed film prior to capillary condensation is necessary, and c) the scattering curves although at high-Q values coincide, at low-Q values are different indicating different microscopic states. That is, at a common point the system holds different metastable states sustained by hysteresis effects. These metastable states are the ones which highlight the way of a system back to a return point memory (RPM). Entering the hysteresis loop from different RPMs different histories are implanted to the paths toward the common point. Although in general the memory points refer to relaxation phenomena, they also constitute a characteristic feature of capillary condensation. Analogies of the no-passing rule and the adiabaticity assumption in the frame of adsorption hysteresis are discussed.

Highlights

In the last ten years considerable effort has been made on studying capillary condensation/ evaporation phenomena in mesopore systems
Since the complexion diagrams at X indicate that υCX-υAX>0 it must be ΔwX = wAXwCX>0; where ΔwX is a correction for the adsorbed film that is needed in order Everett’s theorem-6 to be valid
Theorem-6 of the domain theory was examined by conducting adsorption in situ with small angle x-ray scattering (SAXS)

Summary

Introduction

In the last ten years considerable effort has been made on studying capillary condensation/ evaporation phenomena in mesopore systems. To this end, new materials with a well-defined pore geometry together with advanced computational modelling and simulation techniques have been employed [1,2,3,4,5,6,7,8,9,10,11,12,13]. Mesoporous materials are mostly known to exhibit a type IV adsorption isotherm with a hysteresis loop [15]. Adsorption [16,17,18,19,20,21] is only an example among several other physical processes (e.g. magnetism [22], solid transitions [23], contact angle [24], etc) that exhibit

Results

Discussion

Conclusion