  Microgels are elastic and deformable particles with a hybrid nature between
that of polymers and colloids and unconventional behaviours with respect to
hard colloids. We investigated the dynamics of a soft microgel made of
interpenetrated polymer networks of PNIPAM and PAAc by means of coherent X-ray
and light scattering techniques. By varying the particle softness through PAAc
content we can tune at wish the fragility of IPN microgels. Interestingly we
find the occurrence of a dynamical crossover at a critical weight concentration
which leads to an evolution of the structural relaxation time from a
super-Arrhenius to a slower than Arrhenius behaviour, a minimum for the shape
parameter of intensity autocorrelation function and the emerging of distinct
anomalous mechanisms for particle motion. This complex phenomenology can be
described by a Fickian diffusion at very low concentrations, an effective non
Fickian anomalous diffusion at intermediate values and a ballistic motion well
described within the Mode Coupling Theory.
