Monolayer formation of PBLG–PEO block copolymers at the air–water interface

Abstract

Physicochemical properties of PBLG (poly( γ-benzyl- l-glutamate))–PEO (poly(ethylene oxide)) diblock copolymers composed of PBLG as the hydrophobic rod component and PEO as the hydrophilic component were investigated at the air–water interface. Surface pressure–area isotherms obtained by the Wilhelmy plate method provide several variables such as molecular size, compressibility of PEO, and the free energy change of the PBLG–PEO block copolymer. GE-1 ( M w of PBLG:PEO = 103,700:12,000 ), with a relatively longer rod, has negative temperature effects and GE-3 ( M w of PBLG:PEO = 8400:12,000 ), with a relatively shorter rod, shows a positive temperature effect because of the large entropy loss. These competitions were based on the block size of PBLG and PEO and were affected by various microstructures of the PBLG–PEO diblock copolymer. Monolayer aggregations transferred onto mica from the air–water interface were analyzed with AFM. AFM images of GE-1 monolayers show cylindrical micelles, but the self-assembled structure has many large domains. The monolayer of GE-2 ( M w of PBLG:PEO = 39,800:12,000 ), which has a medium size rod, forms a spherical structure at the air–water interface. Monolayers of GE-3, with a short rod length, form bilayer structures. These results demonstrate that the microstructures of PBLG–PEO diblock copolymers are related to free energy changes between rod and coil blocks.