Enhancement of liquid-liquid phase transition under shear flow

Kyohei Takae

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arXiv · 2610.25243

Enhancement of liquid-liquid phase transition under shear flow

Kyohei Takae

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Abstract

In a liquid--liquid transition (LLT), a single-component liquid transforms into another liquid with different density and viscosity. Flow therefore couples to the transition, but the effect of shear flow is not understood. Here we investigate the LLT under shear with a two-order-parameter hydrodynamic model in which the viscosity depends on the non-conserved structural order parameter. Under shear, a fluctuation of the order parameter drives a compressional flow through the viscosity, and the resulting density change enhances the order parameter fluctuation. In a linear analysis, this feedback destabilizes the metastable liquid above a critical shear rate $\dotγ_{\rm c}$ for wavevectors in particular directions. Because the flow rotates the wavevector, a fluctuation grows only for a finite time duration, and its amplification is determined by the dimensionless shear rate $\dotγ/\dotγ_{\rm c}$ and the second dimensionless number $Λ$, the ratio of the thermodynamic relaxation rate of the order parameter to $\dotγ_{\rm c}$. In hydrodynamic simulations, shear above about $\dotγ_{\rm c}$ induces the transition in the metastable region when $Λ\gtrsim1$. The transition proceeds by nucleation of domains whose morphology becomes anisotropic. The incubation time decreases and the onset of the viscosity increase is accelerated as $\dotγ$ and $Λ$ increase. These results imply that the shear rate is a control variable of LLT in addition to temperature and pressure, selecting whether and how a metastable liquid transforms.

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Kyohei Takae. 2026-10-18. Enhancement of liquid-liquid phase transition under shear flow. https://arxiv.org/abs/2610.25243

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