Paper Number
PO58 

Session
Poster Session

Title
High frequency viscoelasticity of jammed microgel suspensions

Presentation Date and Time
October 12, 2022 (Wednesday) 6:30

Track / Room
Poster Session / Riverwalk A

Authors (Click on name to view author profile)

  1. Di Dio, Bruno F. (ESPCI Paris - PSL, Molecular, Macromolecular Chemistry and Materials)
  2. Athanasiou, Thanasis (IESL-FORTH)
  3. Vlassopoulos, Dimitris (FORTH and University of Crete)
  4. Cloitre, Michel (ESPCI Paris - PSL, Molecular, Macromolecular Chemistry and Materials)

Author and Affiliation Lines (in printed abstract book)
Bruno F. Di Dio1, Thanasis Athanasiou2, Dimitris Vlassopoulos3 and Michel Cloitre1
1Molecular, Macromolecular Chemistry and Materials, ESPCI Paris - PSL, Paris, France; 2IESL-FORTH, Heraklion, Greece; 3FORTH and University of Crete, Heraklion, Greece

Speaker / Presenter 
Di Dio, Bruno F.

Keywords
experimental methods; computational methods; colloids; emulsions; gels; glasses; jammed systems; rheometry techniques; suspensions

Text of Abstract
We investigate the linear storage and loss moduli of jammed microgel suspensions over a range of frequency from 10-2 rad.s-1 to 5x103 rad.s-1 using a conventional rotational rheometer and a home-made sliding-plate piezo-rheometer [1]. At low frequencies, G’ exhibits a plateau value, G0, that increases linearly with the distance to the jamming transition. G’’ is much smaller and is characterized by a shallow minimum. At high frequencies, both moduli increase with a power-law dependence on frequency. Near the jamming point, they are nearly superimposed and the power-law exponent is close to 0.5. Far from it, G’ is larger than G” and the values of the exponents decrease. The moduli measured at different concentrations and solvent viscosities, ηs, collapse onto master curves when the frequency is rescaled by the characteristic time scale ηs/G0 and the moduli by G0. We discuss these results in the context of recent particle dynamics simulations of soft particles interacting through elastic repulsive forces [2]. The simulations recover the experimental behavior of G’’, which is interpreted in terms of short range lubrication flow between particles. However, the predicted storage modulus tends to a plateau value at high frequencies, which echoes to the behaviour of hard sphere glasses. We examine possible sources of disagreement between experiments and simulations: (i) the existence internal deformation modes in microgels not present in simulations; (ii) the inability of simulations to take into account the structure and mobility of microgel interfaces, which can affect the viscoelasticity of colloidal suspensions at high frequencies [3]. This calls for further investigations using other types of soft colloids such as nanoemulsions. [1] T. Athanasiou, G. K. Auernhammer, D. Vlassopoulos, G. Petekidis, Rheo. Acta. 2019, 58, 619. [2] T. Liu, F. Khabaz, M. Cloitre, R. T. Bonnecaze, J. Rheol. 2022, 66, 293. [3] B. Schroyen, C.-P. Hsu, L. Isa, P. Van Puyvelde, J. Vermant, Phys. Rev. Lett. 2019, 122, 218001.