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Based on thermodynamic non-equilibrium phenomena, blend films of poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) (50/50) with a compositional gradient structure were successfully prepared by evaporation of a PLA/PEO chloroform solution in the open. The drying occured at non-equilibrium conditions, and we were able to regulate and control the non-equilibrium state. The formation of the compositional gradient structure was confirmed by polarized optic microscopy (POM) and attenuated total reflectance Fourier transformed infrared (ATR-FT/IR) mapping. It was found that PLA concentrates at the air-side (at which thermal energy flows out), while PEO concentrates at the glass-side (at which energy flows in). The composition of the resulting films changes gradually along the energy dissipation direction. The non-equilibrium state is the major factor that affects the formation of gradient structure. [ABSTRACT FROM AUTHOR]