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 (π−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 π−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 π−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.