Time Dependent Aspects of Adsorption: Evaluating the Lifetimes within the Hysteresis Loop
When fluids adsorb in mesoporous material in contact with a vapour reservoir, the phenomenon of hysteresis occurs frequently. It piques my interest because it appears to contradict thermodynamics, which states that a system’s response to a set of boundary conditions is unique, regardless of the system’s history. It is, on the other hand, reproducible in experiments and through all computer simulation methods. Many authors have proposed that either or both branches of a double valued adsorption isotherm must be metastable in order to solve this problem. A metastable condition is distinguished by a finite lifetime against decay into the ground state. However, there is no experimental evidence that the adsorption isotherm within the hysteresis loop is time dependent, and we are unaware of any attempt in the literature to estimate the lifetime of either of the adsorption isotherm branches using computer simulation. We present a reliable estimate for the lifetime of the states within the hysteresis loop in this contribution. We discover that even the shortest lived states have lifetimes that are several times the age of the universe and, as a result, are practically stable states. As a result, the concept of bistability (or, in some cases, multistability) appears appropriate for describing the adsorptio hysteresis loop. Certain thermodynamic laws clearly do not apply to confined systems. For the first time, the current work attempts to formulate a time dependent theory for confined thermodynamics, allowing access to the lifetime of states within the hysteresis loop. Certain thermodynamic laws clearly do not apply to confined systems. For the first time, the current work attempts to formulate a time dependent theory for confined thermodynamics, allowing access to the lifetime of states within the hysteresis loop.
Author (S) Details
Dr. Harald Morgner
Wilhelm Ostwald Institute for Physical and Theoretical Chemistry, Faculty of Chemistry and Mineralogy, University Leipzig, Linnéstreet 2, D-04103 Leipzig, Germany.
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