Spontaneous evolution of self-assembled phases from anisotropic colloidal dispersions

Abstract

We demonstrate spontaneous evolution of various self-assembled phases from a homogeneous aqueous dispersion of high aspect ratio Montmorillonite (MMT, platelet diameter ~250 nm and thickness 1 nm) nanoclay platelets based on the observations made over a period of 4 years. The phase diagram for this system in salt-free suspensions in normal pH conditions using rheology, light scattering, and dilution experiments was established, and we have noticed that these suspensions do undergo nontrivial phase evolution yielding formation of equilibrium fluids and gels and aging dynamics. This observation showed that the yield stress dependence on the concentration of clay followed a power-law behavior similar to low aspect ratio Laponite nanoclay dispersions. During the initial period, all dispersions formed stable sols, and with aging network-like structures were found to form via two routes not reported hitherto: one for below gelation concentration by phase separation and another for above the same, through equilibrium gelation resembling the Laponite nanoclay system, where existence of patchy colloids, equilibrium gels, and empty liquids was observed experimentally.

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Acknowledgments

RKP and NJ acknowledge receipt of Senior and Research Fellowship from Council of Scientific and Industrial Research and University Grants Commission, Government of India, respectively.

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Correspondence to H. B. Bohidar.

Electronic Supplementary Material

ESM 1

† Electronic supplementary material available: The supporting information includes sections on the sample preparation and the methods used (Rheology, DLS, TEM, SEM, viscosity), flow curves (Figure S2), evolution of loss modulus (Figure S3) and elastic modulus (S4) for different concentrations of clay. (DOCX 321 kb)

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Pujala, R.K., Joshi, N. & Bohidar, H.B. Spontaneous evolution of self-assembled phases from anisotropic colloidal dispersions. Colloid Polym Sci 293, 2883–2890 (2015). https://doi.org/10.1007/s00396-015-3651-3

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Keywords

  • Self-assembled phases
  • Equilibrium gels
  • Empty liquids
  • Long-term aging
  • Anisotropic colloids
  • Phase separation