基于强剪切稀化黏塑性基液的磁流变液悬浮机理研究

Magnetorheological fluid (MRF) is a smart material featuring phase change upon an external magnetic field applied, which has wide application prospect in the semi-active control field of automobile, construction, military and other industries. The sedimentation problem of MRFs has been one of the bottlenecks that restricts its practical use. The key issue lies in the contradictory relationship between the stability and the MR performances. There is a truth that MRFs settle in the stationary state (approximately zero shear rate), but their MR performance is generally reflected at high shear rate. Accordingly, a good balance between stability and MR performances could be achieved, if we use a base fluid for MRF with strong shear thinning and viscoplasticity that presents a tiny yield stress at stationary state as well as significantly dropped viscosity at high shear rate. To realize this, this project makes efforts to give a fundamental understanding of the suspension mechanism of MRF. First, the macro-microscopic relationship of each physical parameter is established experimentally. Based on the analytical methodology of gravitational yield parameter, and the micro hydrodynamics and hydrostatics theories, in association with the inspiration by the stable suspension of MRF under a critical yield stress of base fluid and a critical particle concentration respectively, the coupling relationship between the minimum yield stress of base fluid and the critical particle concentration can be obtained via experiment and theoretical analysis. Further, the effect of yield stress of base fluid on the stability of MRF and that of strong shear thinning behavior on the MR performances can be clarified with the first step. Finally, the optimization condition to balance the stability and MR performances can be obtained, which provides a new solution to the sedimentation problem of MRFs.

磁流变液是一种磁敏相变智能材料，在汽车、建筑、国防等工业的半主动控制领域具有广阔的应用前景。磁流变液的沉降问题一直是制约其实用化的瓶颈问题之一，其关键难题在于稳定性与磁流变性能间的对立关系。针对磁流变液沉降发生在静置状态（剪切率趋于零）、但磁流变性能主要体现在高剪切率下这一特点，若采用静置时具有微小屈服应力、高剪切率下黏度大幅下降的强剪切稀化黏塑性基液，便能兼顾稳定性与磁流变性能。项目拟通过研究磁流变液的悬浮机理，从实验上建立各物理参数的宏微观联系，再基于重力屈服参数分析方法、微观流体动/静力学理论，以磁流变液在黏塑性基液临界屈服应力和临界颗粒浓度条件下的稳定悬浮为思路，从实验和理论上得到基液最小屈服应力与临界颗粒浓度间的耦合关系，从而揭示基液屈服应力对磁流变液的稳定性、强剪切稀化效应对磁流变性能的作用机制，得到最优化平衡稳定性与磁流变性能的条件，为解决磁流变液的沉降问题提供一种新的方法。

项目以高黏度线性聚硅氧烷作为强剪切稀化黏塑性基液，研究了基于该基液的磁流变胶泥材料的制备、沉降实验、沉降检测方法与装置、悬浮稳定性机理、高剪切磁流变仪，以及利用外加梯度磁场实现磁流变液抗沉降的创新方法，并在项目开展过程中启发拓展研究了磁流变胶泥缓冲器件、抗沉降固化基磁流变柔性力敏电学特性。阐明了磁流变胶泥的悬浮机理，微观上基液高分子链与磁性颗粒形成了稳定的空间网络结构；宏观上基液的屈服应力使之达到临界重力屈服参数，以及基液微观结构与颗粒相互作用形成的零场屈服应力。建立了磁流变液悬浮稳定性与磁流变效应的综合评价方法，由重力屈服参数评价悬浮稳定性，由修正磁场屈服参数评价磁流变性能。利用横向磁场与垂向梯度磁场可有效提升磁流变液悬浮稳定性，并不影响再分散性能，从非材料角度为解决磁流变液的沉降难题提供了新途径。发现了磁流变弹性体具有超灵敏压力-电容敏感效应，表现出相比传统压容传感器高1~2个数量级的超高灵敏度，且具有200kPa级的宽量程，拓展了磁流变材料的应用场景。此外，设计制作了高剪切率磁流变仪，以及基于介电常数响应机理和磁导率响应机理的两种磁流变液沉降特性检测方法与装置，为磁流变材料的相关参数表征提供了非标测试条件。