An encapsulation of a liquid phase in a thin poly(methyl methacrylate) (PMMA) membrane is achieved in one step by pulsed direct liquid injection (DLI)CVD. The polymer thin film is grown by photo-activation of the gas phase. An original step of the process, described as thermally induced release of internal liquid phase, permits control of the encapsulated liquid during the CVD polymerization. This step highlights a phenomenon that facilitates a conversion of thermal energy into mechanical energy at the nanometer scale. The experimental results are consistent with biomimetic phenomena as biopolymer membranes of living systems, which show how nature makes an efficient use of miniaturization and temperature gradient.