分子界面流变学：脂质膜剪切粘度
Molecular interfacial rheology: Lipid membrane shear viscosity
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中文总结 AI 辅助
该研究开发了分子界面流变学方法，通过平衡态分子动力学模拟结合Mori-Zwanzig形式理论，从脂质膜的横向速度自相关函数中提取波矢相关的剪切粘度，结果经非平衡模拟验证，适用于表征嵌入三维介质的界面系统流变特性。
中文摘要 AI 辅助
我们开发了一种从平衡态分子动力学模拟中提取脂质膜剪切粘度的方法。该方法可表征嵌入三维介质中的一般界面系统的流变特性，我们将其命名为分子界面流变学。在我们的模拟中，平面双层膜及周围水被限制在平行固体壁之间。根据Onsager回归假说，假设膜和水的涨落受控制受限系统的耦合连续介质力学方程支配而弛豫，这些方程预测膜横向速度自相关函数（TVACF）呈指数衰减，衰减速率由膜和水的粘度决定。然而，测得的TVACF表现出阻尼振荡，随后是缓慢衰减的尾部。我们采用Mori-Zwanzig形式理论调和这些行为，并通过TVACF的时间积分提取波矢相关的膜粘度。理论与模拟结果在超过一个数量级的波矢范围内一致，外推至长波长时，两种代表性单组分流体相双层膜的剪切粘度范围为0.064至0.18 pN*us/nm。我们的结果通过对脂质分子施加空间变化的面内体积力的非平衡模拟得到验证，从而验证了分子界面流变学的框架。
英文摘要
We develop a method to extract the shear viscosity of a lipid membrane from equilibrium molecular dynamics simulations. The method characterizes the rheology of general interfacial systems embedded in three-dimensional media; we term it molecular interfacial rheology. In our simulations the planar bilayer and surrounding water are confined between solid, parallel walls. Following Onsager's regression hypothesis, membrane and water fluctuations are assumed to relax according to the coupled continuum-mechanical equations governing the confined system---which predict that the membrane transverse velocity autocorrelation function (TVACF) decays exponentially, at a rate set by the membrane and water viscosities. The measured TVACF, however, exhibits damped oscillations followed by a slowly decaying tail. We reconcile these behaviors using the Mori--Zwanzig formalism, and extract the wavevector-dependent membrane viscosity from the time-integral of the TVACF. Results from theory and simulations agree over a decade of wavevectors, and extrapolating to long wavelengths yields shear viscosities ranging from 0.064 to 0.18 pN*us/nm across two representative single-component, fluid-phase bilayers. Our results are corroborated by nonequilibrium simulations where a spatially varying in-plane body force is applied to lipid molecules, thus validating the framework of molecular interfacial rheology.
发表机构
- McKetta Department of Chemical Engineering, University of Texas（德克萨斯大学麦基塔化学工程系）
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