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<p>We investigate the equilibrium dynamics of binary colloidal hard spheres in microgravity using differential dynamic microscopy (DDM), over a broad range of volume fractions (<i>ϕ</i>) from semi-dilute to highly concentrated suspensions. The intermediate scattering functions exhibit typical features of glass-forming liquids characterized by a double-stretched exponential decay. The system remains ergodic above the mode-coupling theory singularity <i>ϕ</i><sub>C</sub>, where the increase of relaxation time <i>τ</i><sub><i>α</i></sub> follows the generalized Vogel-Fulcher-Tammann law, resulting in a much higher critical density <i>ϕ</i><sub>0</sub>.. Similar phenomena have been observed in previous ground-based experiments. However, compared with the microgravity condition, the relaxation above <i>ϕ</i><sub>C</sub> is much slower under gravity. The characteristic time of the slow decay exhibits a Brownian-like dispersion with wave number, by which an effective diffusion coefficient <i>D</i><sub>S</sub> is determined. The increase of 1/<i>D</i><sub>S</sub> upon supercooling confirms again the above behavior of <i>τ</i><sub><i>α</i></sub>. Our results support the prediction of a lower glass transition density due to the dramatically accelerated aging by gravity. DDM provides a practical method for the space-based research of colloidal suspensions.</p>

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Relaxation dynamics of binary colloidal glass-forming liquids in microgravity

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Zhongyu Zheng,
  • Chen Zhang,
  • Weibin Li,
  • Yuren Wang

摘要

We investigate the equilibrium dynamics of binary colloidal hard spheres in microgravity using differential dynamic microscopy (DDM), over a broad range of volume fractions (ϕ) from semi-dilute to highly concentrated suspensions. The intermediate scattering functions exhibit typical features of glass-forming liquids characterized by a double-stretched exponential decay. The system remains ergodic above the mode-coupling theory singularity ϕC, where the increase of relaxation time τα follows the generalized Vogel-Fulcher-Tammann law, resulting in a much higher critical density ϕ0.. Similar phenomena have been observed in previous ground-based experiments. However, compared with the microgravity condition, the relaxation above ϕC is much slower under gravity. The characteristic time of the slow decay exhibits a Brownian-like dispersion with wave number, by which an effective diffusion coefficient DS is determined. The increase of 1/DS upon supercooling confirms again the above behavior of τα. Our results support the prediction of a lower glass transition density due to the dramatically accelerated aging by gravity. DDM provides a practical method for the space-based research of colloidal suspensions.