Nanoemulsions are known to form �organohydrogels�, solid-like phases with rheology similar to structurally arrested states in attractive near hard sphere suspensions. In this work, we use comprehensive experimental studies to reveal the mechanism of gelation in these systems, providing insight into the mechanics of both soft and hard-sphere colloidal gels at high volume fraction. The use of materials with thermosensitive interdroplet attractions allows for careful examination of the gel transition by combining a number of techniques, including bulk rheology, scattering,  and optical microscopy. We find that the nanoemulsion gels exhibit strong structural and dynamical heterogeneity at length scales significantly larger than the characteristic size of interdroplet clusters. At the onset of gelation, strong cluster-cluster correlations appear. As gelation proceeds, the growth and dynamical fluctuations of these correlations reveal that gelation proceeds by arrested phase separation vis-�-vis spinodal decomposition. Specifically, the dynamics of cluster-cluster correlations are ballistic above a characteristic length scale, which grows linearly with time until complete structural arrest is observed. Finally, by probing the microstructure of the gels under shear deformation, we find that this arrested heterogeneity is critical to explaining the two-step yielding behavior often observed in attractive suspensions.

Heterogeneity and large-scale dynamics in gelling nanoemulsions

246th National Meeting (2013)

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