CRYOELECTRON MICROSCOPY OF BLOCK-COPOLYMERS IN AN ORGANIC-SOLVENT

Solutions of the diblock copolymer polystyrene/poly-2-vinylpyridine (PS/P2VP) in toluene were studied by cryo-transmission electron microscopy following fast freezing of a thin film of the solution in liquid nitrogen. The block copolymer forms spherical micelles which can be visualized using phase contrast microscopy. From the measured diameter of copolymer micelles with different block lengths, it can be concluded that only the poly-2-vinylpyridine core is visible in the electron micrographs, whereas the polystyrene corona is not visible and is largely dissolved into the toluene. The block copolymer micelles are rather stable in the beam and provide enough contrast relative to the amorphous toluene, due to the higher density of the micelles relative to the toluene, to be visible without any staining. This opens the possibility to directly visualize the phase behavior of polymer systems in a volatile solvent, perform time-resolved microscopy, and thus study the dynamics of the formation of different morphologies.