Hierarchical Organization of Poly(ethylene oxide)-block-poly(isobutylene) and Hydrophobically Modified Fe2O3 Nanoparticles at the Air/Water Interface and on Solid Supports

Langmuir monolayers and Langmuir-Blodgett (LB) Film morphologies of block copolymers and hydrophobically modified iron oxide nanoparticles were studied by surface pressure-mean molecular area (pi-mmA) measurements and by tapping mode atomic force microscopy (AFM). The amphiphilic diblock copolymers consisted of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic poly(isobutylene) (PIB) block. The pi-mmA isotherm of PEO97-b-PIB37 (the subscripts refer to the respective degrees of polymerization) at the air/water interface had an extended plateau reflecting the extension of PEO chains into the water subphase at a surface pressure of 10 mN . m(-1), which is absent for the more hydrophobic PEO19-b- PIB130. Iron oxide (Fe2O3) nanoparticles capped with oleic acid ligands as the shell were dispersed in the amphiphilic block copolymers at the air/water interface to prevent macroscopic aggregation of the particles, When the nanoparticles were mixed with PEO97-b-PIB37, using a particle to polymer chain ratio of 1:100, macroscopic aggregation of the nanoparticles was not observed, and the pi-mmA isotherm was dominated by PEO97-b-PIB37. Monolayers of block copolymers were transferred at different surface pressures from the air/water interface to hydrophilic silicon substrates using the Langmuir-Blodgett technique. The AFM images of PEO97-b-PIB37 LB films depicted not only the typical finger-like morphology of the crystallized PEO blocks but also PIB blocks arranged in vertical columns growing perpendicular to the substrate surface. The columns are characteristic for PEO19-b-PIB130 LB films after transfer at high surface pressures and can be assigned to a mesomorphic PIB phase with ordered chains. Finally, it was observed that small clusters of a few Fe2O3 nanoparticles occupy the top of PIB phases after compression and transfer of the block copolymer nanoparticle mixtures to solid supports.