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Micromachines 2019, 10(2), 105; https://doi.org/10.3390/mi10020105

Micro-Surface and -Interfacial Tensions Measured Using the Micropipette Technique: Applications in Ultrasound-Microbubbles, Oil-Recovery, Lung-Surfactants, Nanoprecipitation, and Microfluidics

1
Institute for Molecular Medicine, University of Southern Denmark, Odense 5230, Denmark
2
Department of Mechanical Engineering and Material Science, Duke University, Durham, NC 27708, USA
3
School of Pharmacy, University of Nottingham, Nottingham, NG7 2RD, UK
*
Author to whom correspondence should be addressed.
Received: 14 December 2018 / Revised: 23 January 2019 / Accepted: 25 January 2019 / Published: 1 February 2019
(This article belongs to the Special Issue Microscale Surface Tension and Its Applications)

Abstract

This review presents a series of measurements of the surface and interfacial tensions we have been able to make using the micropipette technique. These include: equilibrium tensions at the air-water surface and oil-water interface, as well as equilibrium and dynamic adsorption of water-soluble surfactants and water-insoluble and lipids. At its essence, the micropipette technique is one of capillary-action, glass-wetting, and applied pressure. A micropipette, as a parallel or tapered shaft, is mounted horizontally in a microchamber and viewed in an inverted microscope. When filled with air or oil, and inserted into an aqueous-filled chamber, the position of the surface or interface meniscus is controlled by applied micropipette pressure. The position and hence radius of curvature of the meniscus can be moved in a controlled fashion from dimensions associated with the capillary tip (~5–10 μm), to back down the micropipette that can taper out to 450 μm. All measurements are therefore actually made at the microscale. Following the Young–Laplace equation and geometry of the capillary, the surface or interfacial tension value is simply obtained from the radius of the meniscus in the tapered pipette and the applied pressure to keep it there. Motivated by Franklin’s early experiments that demonstrated molecularity and monolayer formation, we also give a brief potted-historical perspective that includes fundamental surfactancy driven by margarine, the first use of a micropipette to circuitously measure bilayer membrane tensions and free energies of formation, and its basis for revolutionising the study and applications of membrane ion-channels in Droplet Interface Bilayers. Finally, we give five examples of where our measurements have had an impact on applications in micro-surfaces and microfluidics, including gas microbubbles for ultrasound contrast; interfacial tensions for micro-oil droplets in oil recovery; surface tensions and tensions-in-the surface for natural and synthetic lung surfactants; interfacial tension in nanoprecipitation; and micro-surface tensions in microfluidics. View Full-Text
Keywords: micropipette-technique; air-water surface; oil-water interface; soluble surfactant; insoluble lipids; “black lipid films”; “droplet-interface-bilayers”; equilibrium; dynamic; adsorption; gas-microbubbles; oil-microdroplets; lung-surfactants; nanoprecipitation; microfluidics micropipette-technique; air-water surface; oil-water interface; soluble surfactant; insoluble lipids; “black lipid films”; “droplet-interface-bilayers”; equilibrium; dynamic; adsorption; gas-microbubbles; oil-microdroplets; lung-surfactants; nanoprecipitation; microfluidics
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Needham, D.; Kinoshita, K.; Utoft, A. Micro-Surface and -Interfacial Tensions Measured Using the Micropipette Technique: Applications in Ultrasound-Microbubbles, Oil-Recovery, Lung-Surfactants, Nanoprecipitation, and Microfluidics. Micromachines 2019, 10, 105.

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