Dynamic Light Scattering Studies of Polymer Chain Dynamics Under One-Dimensional Shear Flow

柔性聚合物链在分流解决方案中显示扩散运动到链段的热通量。动态光散射光谱仪提供了关于跨横向扩散协同效应和链内部放松时间的直接信息。However，实验结果并没有完全从视图的理论和分子点解释出来。主要原因可能是要进行Oseen近似，因为它已经被定义用于描述链段上的氢动力学相互作用。这是众所周知的，当不容易的流体被设置在一个维度的流动中， E。g.，Couette Flow， the Navier-Stokes equation确切地描述了流体的氢动力学及其确切的解决方案，在没有流体的情况下，任何接近氢动力学相互作用的情况下，它提供了悬浮粒子的扩散协同作用。在这项工作中，我们将聚合物链放入这样的一个尺寸的Couette流动，并通过动态光散射技术研究聚合物链的动力学。We poured dilute solutions of polystyrene （Mw= 7.76 x10 ^5） and poly （alpha-methylstyrene） （Mw= 2.7 x10 ^6） in benzene （good solvent for both polymers） into the gap between an inner rotating and an outer rest cylinders of a coaxial rotating cylinder viscometer。An eddy-current drive of the inner cylinder yielded a very low shear flow intohe range of 0.57 - 5.3 sec^\-1\。从溶液中散射光的时间相关函数被时间间隔相关器测量，然后分析以估计Couette流中的跨式干扰协同效应和聚合物链的内部动力。Tt找到了一种链动力学揭示的剪切率相关行为，但它是一个小的、有限的剪切率，即内部动力消失，并且翻译差异协同可以在没有任何雄心的情况下检测到。

Flexible polymer chains in dilute solution show the diffusion motion due to thermal fluctuation of the chain segments. Dynamic light scattering spectroscopy has given direct information on the trans-lational diffusion coefficient and the internal relaxation times of the chains. However, the experimental results has not fully been explained from the theoretical and molecular point of view. The main reason might be due to Oseen approximation which has been customarily used to describe the hydrodynamic interaction exerted on the chain segments. It is well known that when the incompressible fluid is set in an one-dimensional flow, e. g., Couette flow, the Navier-Stokes equation describes exactly the hydrodynamics of the fluid and its exact solution gives the diffusion coefficient of suspended particles in the fluid without any approximation to the hydrodynamic interaction. In this work, We put the polymer chain into such an one-dimensional Couette flow and study the polymer chain dynamics through the dynamic light scattering technique. We poured dilute solutions of polystyrene (Mw=7.76x10^5) and poly (alphaーmethylstyrene) (Mw=2.7x10^6) in benzene (good solvent for both polymers) into the gap between an inner rotating and an outer rest cylinders of a coaxial rotating cylinder viscometer. An eddy-current drive of the inner cylinder yielded a very low shear flow intohe range of 0.57 - 5.3 sec^<-1>. The time correlation function of the scattered light from the solution was measured by a time-interval correlator and was then analyzed to estimate the translaーtional diffusion coefficient and the internal motions of the polymer chains in the Couette flow. Tt is found that the chain dynamics revealed shear-rate dependent behavior, but that at a small finite shear rate the internal motions disappeared and the translational diffusion coefficient could be detected without any ambiguity.