Droplet microfluidics is a branch of microfluidics that uses a two-phase liquid system (i.e. oil and water, generally speaking) to distribute or sequester materials of interest into a multitude of immiscible droplets. This is typically achieved by flowing one solution containing the material into a microfluidic device then injecting a second solution in spurts at relatively high flow rate through both sides of a cross-junction. The effect is to pinch off droplets of the first solution and suspend them in the second, creating an emulsion. Because the fluid continues to flow through narrow channels at prescribed rates, the drops are separated from each other by the second phase, preventing them from touching and thereby mixing. Addition of small amounts of drop-stabilizing surfactant to the second phase can reinforce this immiscibility effect even after that phase is removed.