Paper Number
SC13 

Session
Suspensions, Colloids and Granular Systems

Title
A high frequency rheological study of partially aggregated colloidal dispersions

Presentation Date and Time
October 9, 2017 (Monday) 5:00

Track / Room
Track 3 / Crystal C

Authors (Click on name to view author profile)

1. Schroyen, Bram (KU Leuven)
2. Van Puyvelde, Peter (KU Leuven)
3. Vermant, Jan (ETH Zurich)

Author and Affiliation Lines (in printed abstract book)
Bram Schroyen¹, Peter Van Puyvelde¹, and Jan Vermant^2
1KU Leuven, Leuven, Belgium; ²ETH Zurich, Zurich, Switzerland

Speaker / Presenter 
Schroyen, Bram

Text of Abstract
A critical parameter for the performance of nanomaterials is the degree to which the fillers are dispersed in the matrix. Due to their colloidal nature, dispersing nanoparticles is complex and there is a clear need for tools to assess the dispersion state. Rheology offers significant advantages for characterizing dispersions with respect to optical or scattering techniques since it can present a global view of the microstructure. In order to quantify the degree of dispersion of partially aggregated suspensions based on rheological measurements, a new approach is proposed. Information on the dispersion state is classically inferred from the low frequency elastic modulus as its behavior is mainly dictated by the particle contribution. However a more direct relationship between rheological properties and degree of dispersion can be derived from the loss modulus in the high frequency hydrodynamic limit. In this limit the loss modulus is not influenced by colloidal interactions but depends only on the hydrodynamic volume occupied by the particles or aggregates. As such, the individual building blocks of the dispersion can be probed even when being part of a global network. A homebuilt piezo shear rheometer with optimized alignment and measurement sensitivity is constructed to extend the accessible frequency range. Measurements on partially dispersed spherical silica particles prove the need for this extended range to enter in the hydrodynamic region. In this region, the relative loss modulus reaches a plateau. The asymptotic behavior towards this high frequency limit depends on the relative strength of the colloidal to the hydrodynamic interactions. A dispersion quality index is derived by quantifying the distance of the high frequency loss modulus to the hard sphere case for finely dispersed particles by means of a hydrodynamic viscosity model. This index can for instance be used to follow the evolution of the degree of dispersion as a function of mixing intensity and time.