Structure of highly packed microgel particles

We study the structure of concentrated suspensions of ionic microgel particles. In the shrunken state, the particles are essentially charged hard spheres and crystallize at high enough volume fractions. When swollen, however, we find no sings of crystallization, as shown by light and neutron scattering experiments; this is the case irrespective of particle concentration. Instead, the scattered intensity is characterized by the presence of two distinct peaks at low and high scattering wave vectors. Surprisingly, we find that the shift of the peaks follow identical scaling laws with concentration both above and below random close packing. The scaling is different for both peaks indicating they have a different physical origin. While the first maximum seems to be related to the structure of the system, the second peak seems to arise from charge correlations inside the microgel particles.