Dependence of ultrasonic propagation properties of functional fluids on cluster formation

实验研究了均匀磁场作用下超声波在水基和煤油基磁流体以及磁流变液中的传播速度。超声波传播速度的测量是在测量施加磁场的经过时间的同时并且在改变磁场强度和超声波传播方向与磁场方向之间的角度的同时进行的。由于团簇的形成，超声波的传播速度随外加磁场的时间和强度而变化。在不同的磁场角度下，观察到超声波传播速度的各向异性。在HC-50中，超声波传播速度随磁场的变化百分比小于W-40。HC-50中形成的链状团簇似乎比W-40中形成的链状团簇小。这些有趣的结果被认为是依赖于特性的流变性质的磁性流体，是与表面活性剂施加到颗粒。超声波在磁流变液中传播速度的变化率比在磁性液体中的大一个数量级，并且随着磁场的施加而发生突变，我们得到了一些与超声波传播速度有关的有趣的实验结果。这些结果是以前的理论方法所没有预测到的。在现阶段，有必要进行更多的各种和详细的实验，以澄清产生这些超声波在磁性和MR流体中的传播特性的机制。

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.