粘弹性流体中几何控制的弛豫谱
Geometry-Controlled Relaxation Spectra in Viscoelastic Fluids
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- Universität Konstanz（康斯坦茨大学）
- Georg-August-Universität Göttingen（哥廷根大学）
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中文总结 AI 辅助
本研究证明粘弹性流体的宽弛豫谱可由激励几何而非材料复杂性产生，扭转驱动将距离转化为弛豫时间，形成长寿命空间记忆，为机械记忆元件提供新途径。
中文摘要 AI 辅助
软物质通过弛豫过程储存、耗散和释放机械应力，这些过程通常跨越多个时间数量级。此类弛豫谱被广泛用于推断材料内部动力学，并通常被视为微观复杂性、无序性或异质性的指纹。在此，我们展示了一个宽弛豫谱可以由机械激励本身的几何结构产生。利用在蠕虫状胶束流体中旋转驱动的胶体二聚体（该流体具有约一秒量级的占主导的体相弛豫时间），我们证明扭转驱动将距驱动物体的距离转化为弛豫时间。这产生了一个由几何控制的弛豫模式层级：取向回弹持续数百秒，并在相当长的时间内编码过去的扭矩协议。粒子测速显示角动量从探针快速输运出去，与储存的扭转应力的缓慢弛豫形成对比。一个连续壳模型捕捉了观察到的回弹动力学以及在空间限制下对长寿命贡献的选择性抑制。我们的结果表明，几何结构可以将具有简单内禀弛豫的材料转变为具有长寿命、空间依赖性记忆的系统，这提示了一种通过机械激励而非组分来调节材料动力学的途径，并对微观机械记忆元件具有潜在意义。
英文摘要
Soft materials store, dissipate and release mechanical stresses through relaxation processes that often span many orders of magnitude in time. Such relaxation spectra are widely used to infer internal material dynamics and are usually regarded as fingerprints of microscopic complexity, disorder, or heterogeneity. Here we show that a broad relaxation spectrum can instead be generated by the geometry of mechanical excitation itself. Using rotationally driven colloidal dimers in a wormlike micellar fluid with a dominant bulk relaxation time of order one second, we demonstrate that torsional driving converts distance from the driven object into relaxation time. This produces a geometry-controlled hierarchy of relaxation modes: orientational recoils persist for hundreds of seconds and encode past torque protocols over comparably long times. Particle velocimetry reveals rapid angular-momentum transport away from the probe, in contrast to the slow relaxation of stored torsional stress. A continuum shell model captures the observed recoil dynamics and the selective suppression of long-lived contributions under spatial confinement. Our results show that geometry can transform a material with simple intrinsic relaxation into a system with long-lived, space-dependent memory, suggesting a route to tune material dynamics through mechanical excitation rather than composition, with potential implications for microscopic mechanical memory elements.
