Crystal structure of highly concentrated, ionic microgel suspensions studied by small-angle x-ray scattering.

We present a small-angle x-ray scattering study of the crystal structure formed by pH -sensitive poly(2-vinylpyridine) microgel particles with 5 wt % of cross-linker. We focus on highly swollen particles and explore concentrations ranging from below close packing to well above close packing, where the particles are forced to shrink and/or interpenetrate. The crystal structure found from poly- as well as monocrystalline domains is random hexagonally close packed, as also observed in hard spheres.