Structure and Mechanical Response of Self-Assembled Poly(butadiene)-b-poly(ethylene oxide) Colloids Probed by Atomic Force Microscopy

In this study, the aqueous structure and mechanical response of self-assembled poly(butadiene)-b-poly(ethylene oxide) (PB−PEO) colloids were probed using atomic force microscopy (AFM). It was observed that the structure of these colloids ranged from spherical micelles, wormlike micelles, to polymersomes depending on the diblock composition and method of preparation. At 1 mg/mL of PB−PEO, ordered micelles exhibiting hexagonal packing was observed on glass surfaces. Isotropic wormlike micelles with network and spaghetti-like patterns were also observed. AFM force imaging of closely packed micelles on glass surfaces showed a sharp downward deflection, which implied the existence of a “transition escape” most probably due to a conformational change in the PEO hydrophilic brush upon AFM tip compression. Force curve measurements on micelles and polymersomes indicated that the hydrophobic core has a springlike linear response, while the hydrophilic PEO corona has an exponential response to the applied AFM tip compression force. Taken together, the results of this study shed new light on the structure and mechanical response of self-assembled PB−PEO colloids as a function of copolymer composition and method of preparation.