Complex optical transport, dynamics, and rheology of intermediately attractive emulsions

Abstract

Abstract Introducing short-range attractions in Brownian systems of monodisperse colloidal spheres can substantially impact their structures and consequently their optical transport and rheological properties. Here, for size-fractionated colloidal emulsions, we show that imposing an intermediate strength of attraction, well above but not much larger than thermal energy ( $$\approx 5.6$$ ≈ 5.6 $$k_{\textrm{B}}T)$$ k B T ) , through micellar depletion leads to a striking notch in the measured inverse mean free path of optical transport, $$1/\ell ^*$$ 1 / ℓ ∗ , as a function of droplet volume fraction, $$\phi$$ ϕ . This notch, which appears between the hard-sphere glass transition, $$\phi _{\textrm{g}}$$ ϕ g , and maximal random jamming, $$\phi _{\textrm{MRJ}}$$ ϕ MRJ , implies the existence of a greater population of compact dense clusters of droplets, as compared to tenuous networks of droplets in strongly attractive emulsion gels. We extend a prior decorated core-shell network model for strongly attractive colloidal systems to include dense non-percolating clusters that do not contribute to shear rigidity. By constraining this extended model using the measured $$1/\ell ^*(\phi )$$ 1 / ℓ ∗ ( ϕ ) , we improve and expand the microrheological interpretation of diffusing wave spectroscopy (DWS) experiments made on attractive colloidal systems. Our measurements and modeling demonstrate richness and complexity in optical transport and shear rheological properties of dense, disordered colloidal systems having short-range intermediate attractions between moderately attractive glasses and strongly attractive gels.