Anisotropic Hollow Microgels That Can Adapt Their Size, Shape, and Softness*

We have recently shown how to create hollow, anisotropically shaped thermoresponsive microgels, polymeric networks with a solvent filled cavity that are swollen in a good solvent.^[1]Sacrificial elliptical hematite silica particles were utilized as a template for the synthesis of a cross-linked N-isopropylacrylamide (NIPAm) shell. We characterized these microgels using a combination of light, X-ray, and neutron scattering. New form factor models, accounting for the cavity, the polymer distribution and the anisotropy, have been developed for fitting the scattering data. With such models, we demonstrated the existence of the cavity and simultaneously the anisotropic character of the microgels. Finally, the effect of temperature and shell thickness was investigated, showing that changes in size, softness, and aspect ratio are triggered. We believe that these hollow anisotropic microgels represent an attractive model system for fundamental physics (e.g. phase behavior or ordering phenomena) and a variety of applications especially in respect to their responsivity to temperature.
[1]Nickel A.C. et al.,Nano Lett. 2019, doi:10.1021/acs.nanolett.9b03507