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Article

When Thermodynamic Properties of Adsorbed Films Depend on Size: Fundamental Theory and Case Study

1
Department of Structural Engineering, Faculty of Engineering Science and Technology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
2
Porelab, Department of Chemistry, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(9), 1691; https://doi.org/10.3390/nano10091691
Received: 20 July 2020 / Revised: 18 August 2020 / Accepted: 19 August 2020 / Published: 27 August 2020
(This article belongs to the Special Issue Nanoscale Thermodynamics)
Small system properties are known to depend on geometric variables in ways that are insignificant for macroscopic systems. Small system considerations are therefore usually added to the conventional description as needed. This paper presents a thermodynamic analysis of adsorbed films of any size in a systematic and general way within the framework of Hill’s nanothermodynamics. Hill showed how to deal with size and shape as variables in a systematic manner. By doing this, the common thermodynamic equations for adsorption are changed. We derived the governing thermodynamic relations characteristic of adsorption in small systems, and point out the important distinctions between these and the corresponding conventional relations for macroscopic systems. We present operational versions of the relations specialized for adsorption of gas on colloid particles, and we applied them to analyze molecular simulation data. As an illustration of their use, we report results for CO2 adsorbed on graphite spheres. We focus on the spreading pressure, and the entropy and enthalpy of adsorption, and show how the intensive properties are affected by the size of the surface, a feature specific to small systems. The subdivision potential of the film is presented for the first time, as a measure of the film’s smallness. For the system chosen, it contributes with a substantial part to the film enthalpy. This work can be considered an extension and application of the nanothermodynamic theory developed by Hill. It provides a foundation for future thermodynamic analyses of size- and shape-dependent adsorbed film systems, alternative to that presented by Gibbs. View Full-Text
Keywords: adsorption; thin film; nanothermodynamics; small-system; size-dependent; thermodynamics; spreading pressure; entropy of adsorption adsorption; thin film; nanothermodynamics; small-system; size-dependent; thermodynamics; spreading pressure; entropy of adsorption
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MDPI and ACS Style

Strøm, B.A.; He, J.; Bedeaux, D.; Kjelstrup, S. When Thermodynamic Properties of Adsorbed Films Depend on Size: Fundamental Theory and Case Study. Nanomaterials 2020, 10, 1691. https://doi.org/10.3390/nano10091691

AMA Style

Strøm BA, He J, Bedeaux D, Kjelstrup S. When Thermodynamic Properties of Adsorbed Films Depend on Size: Fundamental Theory and Case Study. Nanomaterials. 2020; 10(9):1691. https://doi.org/10.3390/nano10091691

Chicago/Turabian Style

Strøm, Bjørn A., Jianying He, Dick Bedeaux, and Signe Kjelstrup. 2020. "When Thermodynamic Properties of Adsorbed Films Depend on Size: Fundamental Theory and Case Study" Nanomaterials 10, no. 9: 1691. https://doi.org/10.3390/nano10091691

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