Confocal surface tension

Although the scale of typical liquid-gas interfaces is large compared to the resolution of many modern characterisation techniques, they are difficult to observe because the surface of interest is situated beneath the drop of the liquid. The method presented here bypasses this difficulty by solidifying the drop and inspecting the surface directly. Slight shrinkage of the drop when it is subjected to the laser beam of the confocal microscope may cause a problem. Earlier works have used a plasticising drop where this is not a problem [15]. However, the benefit of the present method is that it uses a water-based system with a surface tension similar to that of water. 

Li et al. 48) studied how 1.0 pm particles of polystyrene and poly(methyl methacrylate) interacted when they were melt processed at 180 °C. They observed by confocal microscopy on a hot stage that there was a preferential motion for particles, which they attributed to a buoyancy-driven flow because of the 10% density difference between the polymers. Jang et al. had made a similar observation 49), Li et al. did not consider possible surface-tension induced convection or that droplets could migrate in a temperature gradient, as has been observed by Balasubramaniam et al. for the thermocapillary migration of bubbles 50),... 

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