Abstract: The rheological properties of magnetorheological suspensions containing surfactant with the same anchor group but different solvated group length are studied. The viscosity,magnetorheology and stability of the magnetorheological suspensions with micro-sized particles modified by oleic acid and PMMA and dispersed in silicone oil by means of ultrasonic are tested. Steric repulsion (entropic repulsion)of the absorbed layer on the surface of carbonyl iron (CI)particles is the main factor at low shear rate that makes a decrease in viscosity. However,surfactant layer could induce a hindrance effect on particle movement at high shear rate,resulting in an increased off-state viscosity. Moreover,the magnetorheological suspension with particles modified by oleic acid has stronger magnetorheology response compared to bare CI based magnetorheological suspension and the suspension absorbed PMMA behaves ratherish weaker. Both oleic acid and PMMA promote the stability of the magnetorheological suspensions especially for PMMA. This research provides a reference for the selection of surfactants.

Key words: magnetorheological fluids, oleic acid, poly(methyl methacrylate)(PMMA), rheology, viscosity, stability

摘要： 主要研究了拥有相同极性基团不同长度的非极性基团的表面活性剂对磁流变液流变行为的影响。分别以油酸、聚甲基丙烯酸甲酯修饰后的羰基铁粉为可磁化颗粒，硅油为载液，经过超声分散制备磁流变液。黏度测试表明，低速剪切时，颗粒表面表面活性剂层的空间位阻作用（熵斥力）起主导作用，黏度降低；高速剪切时，表面活性剂层又会增大颗粒的内摩擦，使黏度增加。通过流变模型的定量分析也印证了上述结论。磁流变测试表明，油酸为表面活性剂的磁流变液对磁场有更强烈的响应，形成更强的链束结构，屈服应力增大，而聚甲基丙烯酸甲酯的作用相反。两种表面活性剂都明显改善磁流变液的沉降稳定性能，降低了沉降速率与最终沉降量。本研究为磁流变液表面活性剂的选用提供了参考。

关键词: 磁流变液, 油酸, 聚甲基丙烯酸甲酯, 流变学, 黏度, 稳定性