The surface chemistry of two series of poly(ethylene oxide) (PEO)-containing biodegradable poly(L-lactic acid) (PLLA) matrix systems has been investigated using time-of-light SIMS (ToF-SIMS) and XPS. The two systems are (1) PLLA blend matrices with an amphiphilic Pluronic (R) P-104 surfactant, P(EO)(27)-b-P(PO)(61)- P(EO)(27), and (2) PLLA-b-PEO diblock and PLLA-b-PEO-b-PLLA triblock copolymers. The phase separation is analyzed in determining the surface enrichment of the component and chemical composition at the polymer-air interface. The PEO component is surface-dominant in the blend system in contrast to the surface excess of poly(propylene oxide) (PPO) in pure Pluronic (R) P-104. The block copolymer system shows the surface enrichment of PLLA component. These results can be explained in terms of the change in surface free energy for the block copolymers and the better miscibility of PLLA and PPO against amphiphilic PEO for the blends, respectively. (C) 2008 Elsevier B. V. All rights reserved.