| Whenever a low viscosity fluid displaces a high viscosity fluid in a porous medium or Hele-Shaw cell, the interface is rendered unstable. We show that this so-called Saffman-Taylor instability persists in systems where the interfacial tension is roughly a million times lower than in molecular systems. As our model system we use a mixture of spherical colloids and non-adsorbing polymers, which we study by means of confocal laser scanning microscopy in microfluidic devices. It turns out that at these scales thermal fluctuations, wettability and gravity all play a crucial role in describing the instability. |
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