Nanoscale Phenomena in Functional Materials by Scanning Probe Microscopy

The use of soft materials to synthesize inorganic nanoparticles has recently become a subject of intense research activity, and these systems are well-suited for characterization by atomic force microscopy. In particular, phase imaging in tapping mode could be leveraged toward investigating composite nanomaterials, precisely because of the inherent nanoscale differences in phase and corresponding mechanical properties. Diblock copolymer micelles nowadays are used as nanoscale reactor vessels for the synthesis of different metallic and semiconductor nanoparticles. Characterizing these nanoreactors at each step during the synthesis process helps in developing a controlled reaction inside the micelles. In the study we are presenting, phase imaging was used to characterize polystyrene-b-poly2vinlpyridine (PS-b-P2VP) reverse micelles loaded with zinc acetate in the micelle core. Assuming that the zinc cations had attached to the pyridine units at the core, the bright spots near the center of each micelle were observed at low drive amplitudes. The correlation between the phase and the topographic images helped in estimating the size of the micelle core, as well as in determining if the micelles were successfully loaded. Furthermore, the size of the micelles also was observed to increase upon loading with increasing amounts of zinc acetate. The increase was also observed using dynamic light scattering. Because the micelles were imaged by AFM outside of the solution, the micelle might actually be deformed. To analyze the degree of deformation in the collapsed micelle, dynamic light scattering was used to estimate the hydrodynamic diameter, and found not to differ much from the height profile obtained by tapping mode AFM