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Abstract
Magnetic liquid marbles, an encapsulation of liquid droplet with hydrophobic magnetic particles, show remarkable responsiveness to external magnetic force and great potential to be used as a discrete droplet microfluidic system. In this study, we presented the manipulation of a magnetic liquid marble under an external magnetic field and calculated the maximum frictional force, the magnetic force required for actuating the liquid marbles and the effective surface tension of the magnetic liquid marble, as well as the threshold volume for the transition from quasi-spherical to puddle-like shape. By taking advantage of the unique feature of being opened and closed reversibly, we have proven the encapsulated droplets can be detected optically with a reflection-mode probe. Combining the open-close and optical detection also enables to probe chemical reactions taking place within liquid marbles. These remarkable features offer a simple yet powerful alternative to conventional discrete microfluidic systems and may have wide applications in biomedical and drug discovery.
Highlights
Liquid marbles are liquid droplet-powder encapsulations consisting of a small amount of liquid being covered withDF 1⁄4 2pR2ð1 þ cos heÞðcsl À csvÞ À pR2 sin2 heclv ð1Þ where cij is the interfacial tension (i, j = s, l and v)
Magnetic liquid marbles, an encapsulation of liquid droplet with hydrophobic magnetic particles, show remarkable responsiveness to external magnetic force and great potential to be used as a discrete droplet microfluidic system
We presented the manipulation of a magnetic liquid marble under an external magnetic field and calculated the maximum frictional force, the magnetic force required for actuating the liquid marbles and the effective surface tension of the magnetic liquid marble, as well as the threshold volume for the transition from quasispherical to puddle-like shape
Summary
Since this change is always negative in value, the attachment of hydrophobic particles on the air/liquid interface should always be favorable to stabilize the droplet. The small contact of a liquid marble with the substrate makes it Microfluid Nanofluid (2012) 13:555–564 easy to move without leaking the liquid, and no contamination This feature provides liquid marbles with great potential for discrete droplet microfluidics. The droplets can be actuated by an external electric (Srinivasan et al 2004) or magnetic field (Lehmann et al 2006; Dorvee et al 2004), or an acoustic action (Guttenberg et al 2005) These oil-immersed systems met problems with poor ability to communicate with the outside and potential for liquid–liquid extraction of analytes into the surrounding oil (Abdelgawad et al 2008). Liquid marbles have been reported to be able to reduce the evaporation of liquid because of the coverage of hydrophobic particles (Dandan and Erbil 2009) This makes them promising for applications in discrete droplet microfluidics. The maximum frictional force and the external magnetic force required for magnetically actuating the liquid marbles, the effective surface tension of the magnetic liquid marble, and the threshold volume for the transition from quasi-spherical to puddle-like shape are calculated
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