Liquid beads in an elastic matrix: Rheology of a solid emulsion with phase-changing droplets

Classic viscoelastic systems show correlated storage and loss moduli. To try and decouple them with regards to the structure of the material, we study “solid emulsions” with a crosslinked continuous phase. The rheological properties of emulsions depend on both the continuous and the dispersed phase, as well as the interface between them. Thus, by encapsulating the liquid dispersed phase in a solid elastic matrix, we can create a composite material with tunable rheological properties [1].

The chosen dispersed phase in our “solid emulsion” can solidify at room temperature. This phase change is used to vary the moduli of the dispersed phase. Previous theoretical works have shown that for liquid inclusions we can expect to see different rheological responses depending on the continuous and dispersed phase moduli, the size of the droplets in the matrix and the volume fraction of dispersed phase [2, 3]. However, when the inclusions are solid, the complex modulus should only depend on the continuous phase and volume fraction [4].

We first show the feasibility of a composite system whose storage and loss moduli can be controlled independently, and study the mechanisms for such a decorrelation. For our system, we have observed a decoupling of the storage and loss moduli in the rheological response for liquid insertions in the matrix when varying the volume fraction. When the droplets are solid, we observe however a deviation from the expected behavior solely controlled by the matrix and the volume fraction, that we investigate through rheology and compression-decompression experiments.

 

References:

[1] R. W. Style, R. Tutika, J. Y. Kim, M. D. Bartlett, Advanced Functional Materials, 2020, 31

[2] J. F. Palierne, Rheologica Acta, vol. 29, no 3, p. 204‑214, 1990

[3] R. Pal, Current Opinion in Colloid & Interface Science, vol. 16, no 1, p. 41‑60, 2011

[4] M. Krieger et T. J. Dougherty, Transactions of the Society of Rheology, vol. 3, no 1, p. 137‑152, 1959