Articolo in rivista, 2020, ENG, 10.1021/acs.macromol.9b01560

Relaxation dynamics, softness, and fragility of microgels with interpenetrated polymer networks

Valentina Nigro, Barbara Ruzicka, Beatrice Ruta, Federico Zontone, Monica Bertoldo, Elena Buratti, Roberta Angelini

Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), sede Sapienza, Pz.le Aldo Moro 5, I-00185 Roma, Italy; Dipartimento di Fisica, Sapienza Università di Roma, I-00185 Roma, Italy; Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), sede Sapienza, Pz.le Aldo Moro 5, I-00185 Roma, Italy; Dipartimento di Fisica, Sapienza Università di Roma, I-00185 Roma, Italy; France Univ Lyon, Universitè Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, 69100 Villeurbanne, France; ESRF The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France; ESRF The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France; Istituto per la Sintesi Organica e la Fotoreattività del Consiglio Nazionale delle Ricerche (ISOF-CNR), via P. Gobetti 101, 40129 Bologna, Italy; Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), sede Sapienza, Pz.le Aldo Moro 5, I-00185 Roma, Italy; Dipartimento di Fisica, Sapienza Università di Roma, I-00185 Roma, Italy

Microgels 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

Macromolecules (Online) 53 (5), pp. 1596–1603

Keywords

Colloidal particles, scattering, colloids, gels, amorphous materials

CNR authors

Nigro Valentina, Buratti Elena, Bertoldo Monica, Ruzicka Barbara, Angelini Roberta

CNR institutes

ISOF – Istituto per la sintesi organica e la fotoreattività, ISC – Istituto dei sistemi complessi