Super liquid-repellent surfaces - interactions and gas capillaries

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.Extremt vätskeavvisande ytor har väckt stort intresse de senaste åren. Förutom det stora vetenskapliga intresset finns det många potentiella tekniska tillämpningar, allt från självrengörande material till mikrofluidala system. I denna avhandling studerades hur vätskeavvisande ytor interagerar i vätskor, detta i syfte att undersöka de detaljerade mekanismerna bakom extrem vätskeavvisning. Ett atomkraftmikroskop (AFM) användes för att mäta interaktionskrafterna mellan vätskeavvisande ytor och en mikrosfär i olika vätskor. En uppställning som kombinerade AFM med laserkonfokalmikroskopi (LSCM) möjliggjorde samtidig avbildning för att fånga de mikroskopiska händelserna mellan partikeln och ytan under en kraftmätning. Konfokalbilderna visualiserade framgångsrikt hur de starkt attraktiva krafterna mellan vätskeavvisande ytor orsakas av bildandet av en gasformig kapillär mellan de två ytorna. Liknande långväga krafter med kapillärbildning observerades både i vatten och i vätskor med lägre ytspänning. Dessutom möjliggjorde konfokalbilderna beräkning av kapillärens form och volym och detta visade en ökning av kapillärvolymen under huvuddelen av separationsprocessen. En gasformig film under vätskan vid extremt vätskeavvisande ytor visualiserades med LSCM och slutsatsen drogs att denna gasfilm är ansvarig för bildandet och tillväxten av stora gaskapillärer. Det visade sig att en ökad mängd gas i denna gasfilm påverkade interaktionerna och tillät kapillären att växa sig större under separationen. Vidare visade teoretiska beräkningar utifrån kapillärens storlek och form att ett litet undertryck i kapillären driver gasen att strömma från den gasformiga ytfilmen in i kapillären och detta bidrar till tillväxten under separationen.QC 2020-09-16</p

Ethnicity, educational level and attitudes contribute to parental intentions about genetic testing for child obesity

The objective of this paper is to assess parental beliefs and intentions about genetic testing for their children in a multi-ethnic population with the aim of acquiring information to guide interventions for obesity prevention and management. A cross-sectional survey was conducted in parents of native Dutch children and children from a large minority population (Turks) selected from Youth Health Care registries. The age range of the children was 5–11 years. Parents with lower levels of education and parents of non-native children were more convinced that overweight has a genetic cause and their intentions to test the genetic predisposition of their child to overweight were firmer. A firmer intention to test the child was associated with the parents’ perceptions of their child’s susceptibility to being overweight, a positive attitude towards genetic testing, and anticipated regret at not having the child tested while at risk for overweight. Interaction effects were found in ethnic and socio-economic groups. Ethnicity and educational level play a role in parental beliefs about child overweight and genetic testing. Education programmes about obesity risk, genetic testing and the importance of behaviour change should be tailored to the cultural and behavioural factors relevant to ethnic and socio-economic target groups