Journal
SOFT MATTER
Volume 10, Issue 17, Pages 3122-3133Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3sm52951g
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Funding
- Institute for Collaborative Biotechnologies [W911NF-09-0001]
- U. S. Army Research Office
- National Science Foundation
- National Science Foundation [CMMI-1120724, DMR-1006147, DMR-0944772]
- National Institute of Standards and Technology,
- MRSEC Program of the NSF [DMR 1121053]
- National Science Foundation (NSF) [CBET 0730392, 0854115]
- Directorate For Engineering [1351371] Funding Source: National Science Foundation
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1120724] Funding Source: National Science Foundation
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1006147] Funding Source: National Science Foundation
- Div Of Chem, Bioeng, Env, & Transp Sys [1351371] Funding Source: National Science Foundation
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We elucidate mechanisms for colloidal gelation of attractive nanoemulsions depending on the volume fraction (phi) 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 f 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 f 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.
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