Atomic Force Microscopy Study of Defective Structure in Mixed Langmuir-blodgett Film of Dipalmitoylphosphatidylcholine and Methylmethacrylate

The contacting-mode atomic force microscopy(AFM) was used to investigate the microstructure of the mixed Langmuir-blodgett(LB) film of methylmethacrylate(MMA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC) deposited on hydrophobic quartz substrate.The defects in the LB film and the effect of deposited pressure on the defects were studied.The results revealed that monomer MMA could be congregated in the LB film.When MMA∶DPPC=1∶2 and the deposited surface pressure of 5.0mN/m,liquid-condensed(LC) phase coexisted with liquid-expanded(LE) phase.The LC domains,composed of mixtures of DPPC and MMA,were observed with a diameter of approximately between 3μm and 4μm.And some islands(polymerized MMA aggregation) distributed in the LC domains.While the deposited surface pressure of 15.0mN/m,islands of the polymethylmethacrylate(PMMA) domains were dominated in the LC domains.However,when the molar ratio of MMA was increased to 50%(MMA∶DPPC=1∶1),the percentage of the polymer PMMA increased in the LC domains.It is due to phase segregation in mixed LB films of DPPC,MMA and its polymer PMMA at different MMA ratio and deposited surface pressure.Such round-shaped defects in the mixed LB films of MMA/DPPC could induce round-shaped patterns of calcium oxalate monohydrate crystals.