The yielding of defect-entangled dispersions in a nematic solvent

Oscillatory rheology, at both small and large (LAOS) amplitudes, was performed to measure the dynamic response of a soft solid, formed on dispersing colloids into thermotropic nematic liquid crystal volume fractions ϕ>18%. Due weak homeotropic anchoring nematogens colloid surfaces, Saturn-ring defect line, known as “disclination,” encircles each particle entangles with neighboring disclinations [Wood et al., Science 334, 79–83 (2011)]. We present first experimental investigation yielding behavior resulting gel reveal underpinning physics. Results that frequency composite is independent fraction ϕ, an indication dispersed phase simply increases density spanning without further effect. Beyond linear viscoelastic regime (LVR), LAOS experiments indicate elastoplastic fluid exhibiting strain-hardening shear-thinning behaviors Chebyshev coefficients e3>0 ν3<0, respectively. deduce disclination number nd constant until strain amplitude sufficient break leading beyond LVR. A simple theory introduced revealing Ericksen Er determines onset flow, when Er>1, generating since Frank elasticity resists reorientation molecular alignment within confined domains. Above critical ωc, loss modulus G″ slowly due enhanced viscosity domains, G″∝ω1/2 [Larson, R. G., The Structure Rheology Complex Fluids (Oxford University, 1999), p. 463]. Observation this in small-molecule solvent provides insights physics flow other, more complex, defect-mediated crystalline structures similar properties [Colby, Europhys. Lett. 54, 269–274 (2001); Sahoo Dhara, Liq. Cryst. 44, 1582–1591 (2017); Romo-Uribe, Polym. Adv. Technol. 32, 651–662 (2021)].