This work demonstrates a new mechanism for changing the architecture of microfluidic channels during device operation. This method uses an aqueous solution of a thermally responsive polymer (Pluronic), which undergoes reversible gel formation at elevated temperatures. This gelation temperature is lowered through the presence of sodium phosphate. A phase diagram for this material system is derived from rheometry experiments. Formation of a temporary gel wall in a microfluidic device occurs at the diffusive interface between a Pluronic solution and a sodium phosphate solution. The wall thickness increases along the channel, and it decreases at high flow rates. The wall thickness also increases with saline concentration. These observations are explained through scaling arguments for the diffusion problem and with the established phase diagram.

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