We demonstrate the ability to create ‘liquid-walls’ in hydrophilic microfluidic channels, without the need for hydrophobic patterning. This is achieved by stopping the liquid using sudden expansion in cross-section perpendicular to the flow direction. Further, these walls can be switched off dynamically either manually or by using simple microfluidic logic. The maximum break pressure for these walls is determined by the surface free energy of the liquid, the advancing contact angle of the liquid on substrate and the channel geometry. This system can be used in liquid-gas chemical reactors, passive microfluidic valves, microfluidic pressure switches and in eliminating air entrapment issues.

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