title: On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons.
abstract: Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of 'ink-bottle' pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary.
authors.affiliation: Department of Petroleum and Mechanical Engineering, Hephaestus Lab, Eastern Macedonia and Thrace Institute of Technology, Kavala, St. Lucas 65404, Greece.
authors.forename: A C
authors.initials: AC
authors.lastname: Mitropoulos
authors.affiliation: Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research "Demokritos", Aghia Paraskevi, 153 41, Attica, Greece.
authors.forename: K L
authors.initials: KL
authors.lastname: Stefanopoulos
authors.affiliation: Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research "Demokritos", Aghia Paraskevi, 153 41, Attica, Greece.
authors.forename: E P
authors.initials: EP
authors.lastname: Favvas
authors.affiliation: 1] Department of Petroleum and Mechanical Engineering, Hephaestus Lab, Eastern Macedonia and Thrace Institute of Technology, Kavala, St. Lucas 65404, Greece [2] Department of Chemistry, Laboratory of Adsorption and Catalysis, University of Antwerp, Universiteitsplein 1, B2610 Wilrijk, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Vansant
authors.affiliation: Department of Engineering Science, The University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
authors.forename: N P
authors.initials: NP
authors.lastname: Hankins