Dependence of ultrasonic propagation properties of functional fluids on cluster formation

实验研究了超声在均匀磁场下在水基、煤油基磁流体和磁流变液中的传播速度。超声波传播速度的测量是在测量磁场作用时间的同时，通过改变磁场强度和超声波传播方向与磁场方向的夹角来实现的。由于团簇的形成，超声波的传播速度随时间和外加磁场强度的变化而变化。随着外加磁场角度的变化，超声波传播速度呈现出各向异性，在HC-50中，超声波传播速度随外加磁场的变化百分比小于W-40。HC-50中形成的链状星团似乎比W-40中的要小。这些有趣的结果被认为是依赖于磁性流体的流变性能，这些流变性能与施加在颗粒上的表面活性剂有关。超声在磁流变液中传播速度的百分比变化比在磁流体中大一个数量级，并且随着磁场的施加而突然观察到。我们得到了几个关于超声波传播速度的有趣的实验结果。这些结果是以前的理论方法无法预测的。在现阶段，有必要进行更丰富和详细的实验来阐明这些超声波在磁性和磁流变液中传播特性的产生机制。

Ultrasonic propagation velocities in water-based and kerosene-based magnetic fluids and in an MR fluid under uniform magnetic field are investigated experimentally. Measurements of ultrasonic propagation velocity are carried out while measuring the elapsed time of magnetic field application and while varying the magnetic field intensity and the angle between the direction of ultrasonic propagation and the direction of the magnetic field. The ultrasonic propagation velocity changes with the elapsed time and intensity of an external magnetic field because of the formation of clusters. In varying the angle of the applied magnetic field, anisotropy of the ultrasonic propagation velocity is observed, In HC-50, the percentage change of ultrasonic propagation velocity with applied magnetic field is smaller than that in W-40. It seems that the chain-like clusters formed in HC-50 are smaller than those in W-40. These interesting results are believed to be dependent on characteristic rheological properties of magnetic fluids that are related to surfactants that are applied to the particles. The percentage change of ultrasonic propagation velocity in the MR fluid is one order of magnitude larger than that in magnetic fluids and is observed abruptly with the application of the magnetic field.We obtained several interesting experimental results related to ultrasonic propagation velocities. These results have not been predicted by previous theoretical approaches. At the present stage, it is necessary to carry out more various and detailed experiments to clarify the mechanisms producing these ultrasonic propagation properties in magnetic and MR fluids.