Time‐resolved velocity gradient and optical anisotropy in linear flow by photon correlation spectroscopy
Time‐resolved velocity gradient and optical anisotropy in linear flow by photon correlation spectroscopy
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通过光子相关光谱分析线性流中的时间分辨速度梯度和光学各向异性
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
L. Leal
中科院分区：
文献类型：
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作者：
James J. Wang;Dmitry Yavich;L. Leal
提出了一种时间分辨动态光散射技术，用于测量瞬态可重复流动中的速度梯度。实验技术是通过测量牛顿流体经历一个已知的时间依赖的流动验证。然后将该方法应用于牛顿流体在旋转两辊轧机中的蠕动流动。结果表明，两辊轧机在无界流体中的蠕变流动解析解可以准确地描述滞止点附近的流动。本文还首次测量了两辊轧机启动过程中浓聚溶液的速度梯度随时间的变化规律。该测量结果为粘弹性聚合物液体流动的改变提供了直接证据，并将最终导致对浓溶液在强延伸流中的聚合物动力学的重要见解。动态光散射实验的第二个重要特征是，相关函数的初始大小与聚合物分子的光学各向异性的程度有关，即与聚合物链的几何构型有关。因此，它产生了与双折射相当的聚合物取向和拉伸随时间变化程度的信息，但它是在散射体积所占据的“点”上获得的，而不是像双折射那样作为整个流体的二维平均值。将聚合物构型的测量结果与完全相同流量的双折射数据进行比较。提出了一种时间分辨动态光散射技术，用于测量瞬态可重复流动中的速度梯度。实验技术是通过测量牛顿流体经历一个已知的时间依赖的流动验证。然后将该方法应用于牛顿流体在旋转两辊轧机中的蠕动流动。结果表明，两辊轧机在无界流体中的蠕变流动解析解可以准确地描述滞止点附近的流动。本文还首次测量了两辊轧机启动过程中浓聚溶液的速度梯度随时间的变化规律。该测量结果为粘弹性聚合物液体流动的改变提供了直接证据，并将最终导致对浓溶液在强延伸流中的聚合物动力学的重要见解。动态光散射实验的第二个重要特征是……
A time‐resolved dynamic light scattering technique is presented for measuring the velocity gradient in transient but repeatable flows. The experimental technique is verified via measurements for a Newtonian fluid undergoing a known time‐dependent flow. The method is then applied to the creeping flow of a Newtonian fluid in a corotating two‐roll mill. It is demonstrated that the flow near the stagnation point can be accurately described by an analytical creeping flow solution for a two‐roll mill in an unbounded fluid. The time dependence of the velocity gradient for a concentrated polymer solution in the startup of the two‐roll mill has also been measured, it is believed, for the first time. The measurement provides direct evidence of the modification of the flow for the viscoelastic polymer liquid, and will ultimately lead to significant insights into the polymer dynamics for concentrated solutions in strong, extension‐like flows. A second significant feature of the dynamic light scattering experiment is that the initial magnitude of the correlation function is related to the degree of optical anisotropy of the polymer molecules, i.e., to the geometric configuration of the polymer chains. Thus, it yields information on the time‐dependent degree of polymer orientation and stretch that is equivalent to birefringence, but is obtained at the ‘‘point’’ occupied by the scattering volume rather than as a two‐dimensional average across the whole fluid as in birefringence. This measurement of polymer configuration is compared with birefringence data for the exact same flow.A time‐resolved dynamic light scattering technique is presented for measuring the velocity gradient in transient but repeatable flows. The experimental technique is verified via measurements for a Newtonian fluid undergoing a known time‐dependent flow. The method is then applied to the creeping flow of a Newtonian fluid in a corotating two‐roll mill. It is demonstrated that the flow near the stagnation point can be accurately described by an analytical creeping flow solution for a two‐roll mill in an unbounded fluid. The time dependence of the velocity gradient for a concentrated polymer solution in the startup of the two‐roll mill has also been measured, it is believed, for the first time. The measurement provides direct evidence of the modification of the flow for the viscoelastic polymer liquid, and will ultimately lead to significant insights into the polymer dynamics for concentrated solutions in strong, extension‐like flows. A second significant feature of the dynamic light scattering experiment is ...