Colloidal suspensions of anisotropic particles are widely utilized in consumer products. Homogeneous, physical gelation and vitrification follows rigidity percolation, providing a universal view of dynamical arrest in suspensions of spherical particles (Valadez-Perez et al. PRE, 2013). However, the effect of particle shape on the gel and glass transition boundaries is not well-understood for anisotropic particle suspensions, particularly for colloids with lower aspect ratios (AR, L/D ~ 1-10). The key aim of this study is to clarify the effects of particle shape by combining neutron, X-Ray and light scattering measurements of microstructure with rheology and dynamic light scattering measurements of the dynamics. While prior work in our group identified the conditions for gel formation in model silica rod systems, questions remain about the effects of gravity (Murphy et al., Langmuir 32 2016, 8424-8435) A new thermoreversible colloidal system has been developed, which is composed of hollow, octadecyl-coated silica rods with dimensions of 30-200 nm, tunable aspect ratios, and short-range attractions. Importantly, the gravitational Peclet number is sufficiently low so gravitational settling is unimportant except at the lowest volume fractions (Kim et al. PRL, 2013). SAOS measurements confirm the thermoreversibility of the microstructure and its transition from fluid-state to gel-state. SANS characterizes the form factor of primary particles (shape, core and shell dimensions, brush conformation, size dispersity) as well as the interparticle attraction strength and fractal dimension (D<sub>f</sub>) of the fluid and gel microstructure. Complementary simulations show congruence of dynamical arrest with rigidity percolation, providing a unified view of homogeneous gelation in suspensions of low aspect ratio colloids.

Gelation in colloidal suspensions of rod-like particles of low to moderate aspect ratio

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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