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Super liquid-repellent surfaces - interactions and gas capillaries

Time: Fri 2020-10-09 10.00

Location:, Stockholm (English)

Subject area: Chemistry

Doctoral student: Mimmi Eriksson , Yt- och korrosionsvetenskap, RISE Research Institutes of Sweden

Opponent: Docent Marie Skepö, Lunds universitet

Supervisor: Professor Per M. Claesson, Yt- och korrosionsvetenskap; Professor Agne Swerin, Yt- och korrosionsvetenskap

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Super liquid-repellent surfaces have attracted a lot of interest in recent years. In addition to the large scientific interest there are many potential technological applications ranging from self-cleaning materials to microfluidic devices. In this thesis, interactions between liquid-repellent surfaces in liquids were studied, with the aim to investigate the detailed mechanisms of super liquid-repellence, such as superhydrophobicity and superamphiphobicity. An atomic force microscope (AFM) was used to measure the interaction forces between super liquid-repellent surfaces and a microsphere in different liquids. Additionally, a setup combining AFM with laser scanning confocal microscopy (LSCM) was used, which enabled simultaneous imaging in order to capture the microscopic events between the sphere and the surface during a force measurement. The confocal images successfully visualized how the strongly attractive forces measured between liquid-repellent surfaces are due to the formation of a gaseous capillary bridge between the two surfaces. Similar long-ranged forces with capillary formation and growth were observed both in water and in lower surface tension liquids. Additionally, the confocal images enabled determination of the capillary shape and volume, and the data showed an increase of the capillary volume during the major part of the process of separating the surfaces. A gaseous layer underneath the liquid at super liquid-repellent surfaces was also visualized with LSCM, and it was concluded that this gaseous layer is responsible for the formation and growth of large gas capillaries. It was found that an increased amount of available gas in the gaseous layer influenced the interactions and allowed the capillary to grow larger during separation. Further, theoretical calculations based on the size and shape of the capillary suggested that a small under pressure in the capillary drives the gas to flow from the gaseous surface layer into the capillary, facilitating growth during separation.