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Relaxation Dynamics, Softness, and Fragility of Microgels with Interpenetrated Polymer Networks
journal contribution
posted on 2020-02-20, 22:04 authored by Valentina Nigro, Barbara Ruzicka, Beatrice Ruta, Federico Zontone, Monica Bertoldo, Elena Buratti, Roberta AngeliniMicrogels are elastic and deformable
particles with a hybrid nature
between that of polymers and colloids and unconventional behaviors
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 the 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 behavior, 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.
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Keywords
deformable particlesrelaxation timeFickian diffusioninterpenetrated polymer networksRelaxation Dynamicsweight concentrationIPN microgelsparticle motionPNIPAMintensity autocorrelation functionPAAc contentshape parameterparticle softnessArrhenius behaviorcolloidInterpenetrated Polymer Networks Microgels
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