Miscible solvents are phase separated within microcapsules containing entrapped polymers, thereby creating stable, isolated microenvironments. In particular, we demonstrate that encapsulated polyethyleneimine induces phase separation of toluene and methanol and that this phase separation is well modeled by the Flory-Huggins theory. We further show the generality of microenvironment formation by phase separating tetrahydrofuran and acetone with entrapped polystyrene. (C) 2008 Wiley Periodicals, Inc.