Carbon black particles are rigid fractal colloidal particles obtained through the incomplete combustion of petroleum products. Dispersed in mineral oil, at low volume fractions, the carbon black particles are attractive and assemble thanks to Brownian motion into fractal gels. Carbon black gels belong to the category of shear-reversible gels, meaning that the gels can reform rapidly after being sheared, like shampoo gels but unlike gelatin [1]. Here, I'll discuss the properties of these out-of-equilibrium soft solids using a wide range of experimental techniques such as rheology, ultrasound velocimetry or Small Angle X-ray Scattering. First, I'll discuss how those carbon black gels yield when subject to a constant stress or fatigue experiments (delayed yielding [2]). Second, I'll show how the gel properties are affected by high power ultrasound (rheo-acoustic gels [3]). Finally, I'll discuss how they flow and form tunable gels when shear interfere with the gelation process (multiple metastable gels obtained through flow cessation [4]). [1] Heat-and shear-reversible networks in food: A review. A. V. Kierulf et al. 21, 3405 CRFSFS (2022) [2] Heterogeneous yielding dynamics in a colloidal gel. T Gibaud, D Frelat, S Manneville. Soft Matter 6, 3482 (2010) [3] Rheo-acoustic gels: Tuning mechanical and flow properties of colloidal gels with ultrasonic vibrations. T Gibaud, et al. Phys. Rev. X 10, 011028 (2020) [4] Interpenetration of fractal clusters drives elasticity in colloidal gels formed upon flow cessation. N Dagès, et al. Soft Matter 18, 6645 (2022)
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