Preparation of glass nanopores for the coulter counting of transient nanobubbles

Abstract

Conventional characterisation techniques have so far provided insufficient explanations for the existence of bulk nanobubbles. This thesis proposes an alternative Coulter counting approach that has not yet been applied to nanobubbles and could help elucidate the reasons for their stability. The work herein details the procedure used to obtain glass nanopores and to apply them to the Coulter counting of ultrasonically generated bulk nanobubbles. Tungsten nanoelectrodes are prepared from the electrochemical etching of microwires and the electrochemistry of tungsten is explored in order to characterise and size these electrodes. Nanoelectrodes prepared in this fashion give reproducible diameters of ≈ 100 nm and show electrochemical traits similar to those seen with microelectrodes. Chemical etching of the nanoelectrodes yields glass nanopores that are sized and compared to the nanoelectrodes using voltammetry, simulations, and the Coulter counting of polystyrene nanoparticles. Using a unique differential approach, the sensitivity of the Coulter counting apparatus is shown to increase dramatically. Nanopores are then used to detect and size the transient bulk nanobubbles that are generated during the ultrasonication of potassium chloride solutions with a piston-like emitter. These nanobubbles are distinguished apart from nanoparticles, which are detected in the absence of a local acoustic environment, and microbubbles, which are shown to oscillate in the presence of a local acoustic environment.

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ORCID for Guy Denuault: orcid.org/0000-0002-8630-9492

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