Characterization of micellar film morphologies of semifluorinated block copolymers by AFM

Abstract

The micellar morphologies of well-defined amphiphilic block copolymers composed of 1H,1H-dihydroperfluorooctyl methacrylate (FOMA) and ethylene oxide (EO) blocks with different chain lengths were effectively investigated by using tapping mode-atomic force microscopy (TM-AFM). By spin-casting chloroform solutions, well-ordered spherical micellar films could be obtained for poly(FOMA 10k- b-EO 10k) and poly(FOMA 20k- b-EO 20k) copolymers. The atomic force microscopy (AFM) height and phase image analysis indicated that dark regions of the micelles corresponded to PEO blocks and the light regions were for PFOMA blocks. The spherical micelles with PEO corona and PFOMA core were also identified by transmission electron microscopy (TEM) and X-ray photoelectron spectrometer (XPS) analysis. The core diameters of the block-copolymer aggregates were 20 nm for poly(FOMA 10k- b-EO 10k) and 30 nm for poly(FOMA 20k- b-EO 20k) by TM-AFM, whereas slightly lower values of 17 and 26 nm were obtained from TEM. A detailed study on the inverted morphological change observed in the micelles films after annealing above glass transition temperature ( T g) was also presented.