We describe an in-depth investigation on the dynamics and assembly behavior at polar-apolar interfaces of ferritin-PNIPAAm conjugates (poly-N-isopropylacrylamide). The stabilization of oil-water interfaces by the modified ferritin was investigated by dynamic surface tension measurements and compared to the individual components of the bionanoparticle conjugate, namely, unmodified ferritin and pure PNIMAAm of similar molecular weight. It was found that the modified ferritin, even at a low particle concentration, rapidly reduces the interfacial tension. The difference in interfacial stabilization was also shown by cryo-scanning electron microscopy and scanning force microscopy, which displayed very different morphologies at the polar-apolar interface for the unmodified ferritin, pure PNIPAAm, and the ferritin-PNIPAAm conjugate, respectively. The self-assembly of the ferritin-PNIPAAm was further analyzed by cryo-transmission electron microscopy and fluorescence microscopy, for which a fluorescently labeled polymer was used. Both techniques revealed details on the assembly of the protein-polymer conjugate at the oil-water interface.

SiO2-PNIPAAm core-shell microgels (PNIPAAm=poly(N-isopropylacrylamide)) with various internal cross-linking densities and different degrees of polymerization were prepared in order to investigate the effects of stability, packing, and temperature responsiveness at polar-apolar interfaces. The effects were investigated using interfacial tensiometry, and the particles were visualized by cryo-scanning electron microscopy (SEM) and scanning force microscopy (SFM). The core-shell particles display different interfacial behaviors depending on the polymer shell thickness and degree of internal cross-linking. A thicker polymer shell and reduced internal cross-linking density are more favorable for the stabilization and packing of the particles at oil-water (o/w) interfaces. This was shown qualitatively by SFM of deposited, stabilized emulsion droplets and quantitatively by SFM of particles adsorbed onto a hydrophobic planar silicon dioxide surface, which acted as a model interface system. The temperature responsiveness, which also influences particle-interface interactions, was investigated by dynamic temperature protocols with varied heating rates. These measurements not only showed that the particles had an unusual but very regular and reversible interface stabilization behavior, but also made it possible to assess the nonlinear response of PNIPAAm microgels to external thermal stimuli.

Softness of polymer colloids is vital for the arrangement and density of the colloidal particles at interfaces. On , A. Böker, P. van Rijn et al. present an investigation of SiO2–PNIPAAm core–shell microgels with various internal cross‐linking densities and different degrees of polymerization on the effects of stability, packing and temperature responsiveness at polar–apolar interfaces producing planar assemblies and stable capsules (cover design by C.W. Pester; PNIPAAm=poly(N‐isopropylacrylamide)).