[论文解读] Realizing microrheological response of configurable viscoelastic media with a dynamic optical trap

Sanatan Halder, Manas Khan|arXiv (Cornell University)|Mar 7, 2026

Micro and Nano Robotics被引用 0

一句话总结

该论文展示了一种使用动态引导光学陷阱配置黏弹性介质并提取微流变学响应的实验方法，包括单弛豫与多弛豫模型，以及主动环境。

ABSTRACT

The local viscoelastic (VE) environment governs the motion of an embedded microsphere and consequently, pertinent dynamical phenomena. However, studying such phenomena with varying VE properties remains challenging for various reasons, including the strong coupling among the VE parameters and their dependence on experimental conditions, such as temperature. Here, we demonstrate the experimental realization of configurable VE media with broad variations, wherein the VE properties can be systematically and independently tuned, employing a dynamic optical trap. Specifically, the dynamics of a particle in a slowly diffusing optical trap provides the linear microrheological response of single-relaxation VE fluids, namely, Jeffreys or Maxwell-Voigt (MV) fluids, where the trap strength and its diffusion coefficient regulate the elastic response and the low-frequency viscosity, respectively. We validate this approach by comparing the experimentally observed dynamics of the trapped bead with those of a probe particle in real single-relaxation complex fluids, analytical predictions, and simulation results following harmonically bound Brownian particle with long-time diffusion model describing MV fluids. We extend the applicability of this scheme for realizing the microrheological response of double-relaxation VE media by incorporating appropriately correlated noise in the trap trajectory, signifying its validity for any linear VE media with multiple relaxations. Our scheme can be further extended to realize probe particle dynamics in an active VE environment, e.g., an entangled network of active polymers, by translating the trap along an active Brownian trajectory. Therefore, our scheme enables systematic microrheological studies in VE regimes that are otherwise challenging to realize or not readily accessible with real materials.

研究动机与目标

• 研究在可控 VE 环境中研究微流变学的必要性。
• 开发一种实验方案，独立调节 VE 参数，如高频黏度、平台模量和弛豫时间。
• 证明通过扩散或动态引导的光学陷阱可以实现 MV 与广义Maxwell 模型。
• 通过将陷阱微流变学与真实 VE 流体及仿真比较，验证该方法。
• 将该方案扩展到主动黏弹性环境和多弛豫谱。

提出的方法

• 将探针在 MV 流体中的运动建模为一个谐振束缚的布朗粒子，随陷阱中心的长时间扩散（HBBP with long-time diffusion）。
• 推导 MSD 形式为 <Δr^2(τ)> = 4D_HBBP τ_k (1−e^{−τ/τ_k}) + 4D_HW τ，适用于单弛豫VE流体。
• 通过 GSER 将蠕变压应 J(τ) 与 MSD 关联：J(τ) = (π a / kBT) <Δr^2(τ) >。
• 通过沿预定轨迹引导陷阱实现可配置的 VE，以设定 τ_k、η_s、G_p 和 η_HW。
• 通过引入相关噪声（式 (Eq. 6)）实现双重弛豫，并通过 ABP 轨迹（式 (Eq. 8)）实现主动VE环境的扩展。
• 通过逐步更新 HBBP 位置和 HW 扩散来模拟探针动力学，以计算 MSD 和 J(τ)。

实验结果

研究问题

• RQ1 动态光学陷阱是否能独立调节 VE 环境的高频黏度、平台模量和弛豫时间？
• RQ2 扩散陷阱框架是否能实现真实流体中观察到的单弛豫与多弛豫黏弹性响应？
• RQ3 实验与仿真得到的 MSD 和蠕变压是否与 MV 与 GLVE 的预测一致？
• RQ4 该方法是否可以扩展到主动VE环境以及具有多弛豫模态的广义Maxwell模型？

主要发现

• 单弛豫 VE 流体（MV 流体）显示三个 MSD 调制阶段：短时扩散、弹性平台、以及长时间扩散。
• MSD 对 HBBP with long-time diffusion 模型的拟合在 CTAB–NaSal 和 CPyBr–NaSal 溶液中与实验数据一致。
• 通过陷阱属性（溶剂黏度、陷阱刚度、陷阱扩散）独立调控 η_s、G_p、η_HW，重现 MV 微流变学。
• 通过向陷阱运动加入指数相关噪声实现两次弛豫，产生两个 MSD 平台（式 Eq. 6）。
• 通过沿 ABP 轨迹移动陷阱实现主动 VE 环境，得到弛豫后超扩散行为并最终扩散（式 Eq. 8）。
• 仿真 reproduces 实验 MSDs 与 J(τ)，验证 MV 流体模型及对 GLVE 与主动介质的扩展。