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Issue 17, 2014
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Homogeneous percolation versus arrested phase separation in attractively-driven nanoemulsion colloidal gels

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Abstract

We elucidate mechanisms for colloidal gelation of attractive nanoemulsions depending on the volume fraction (ϕ) of the colloid. Combining detailed neutron scattering, cryo-transmission electron microscopy and rheological measurements, we demonstrate that gelation proceeds by either of two distinct pathways. For ϕ sufficiently lower than 0.23, gels exhibit homogeneous fractal microstructure, with a broad gel transition resulting from the formation and subsequent percolation of droplet–droplet clusters. In these cases, the gel point measured by rheology corresponds precisely to arrest of the fractal microstructure, and the nonlinear rheology of the gel is characterized by a single yielding process. By contrast, gelation for ϕ sufficiently higher than 0.23 is characterized by an abrupt transition from dispersed droplets to dense clusters with significant long-range correlations well-described by a model for phase separation. The latter phenomenon manifests itself as micron-scale “pores” within the droplet network, and the nonlinear rheology is characterized by a broad yielding transition. Our studies reinforce the similarity of nanoemulsions to solid particulates, and identify important qualitative differences between the microstructure and viscoelastic properties of colloidal gels formed by homogeneous percolation and those formed by phase separation.

Graphical abstract: Homogeneous percolation versus arrested phase separation in attractively-driven nanoemulsion colloidal gels

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Article information


Submitted
24 Nov 2013
Accepted
26 Feb 2014
First published
28 Feb 2014

Soft Matter, 2014,10, 3122-3133
Article type
Paper

Homogeneous percolation versus arrested phase separation in attractively-driven nanoemulsion colloidal gels

M. E. Helgeson, Y. Gao, S. E. Moran, J. Lee, M. Godfrin, A. Tripathi, A. Bose and P. S. Doyle, Soft Matter, 2014, 10, 3122
DOI: 10.1039/C3SM52951G

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