Ronzova Alena, Sedlacik Michal, Cvek Martin
Centre of Polymer Systems, University Institute, Tomas Bata University in Zlín, Trida T. Bati 5678, 760 01 Zlín, Czech Republic.
Soft Matter. 2021 Feb 15;17(5):1299-1306. doi: 10.1039/d0sm01785j.
Although smart materials, specifically magnetorheological (MR) fluids, have shown remarkable practical importance, their drawbacks such as an aggregation of magnetic fillers, insufficient compatibility with the carrier liquid, low resistance to corrosion and poor sedimentation stability still cause severe limitations for their broader utilization. To address this challenge, our study presents a facile concept for the coating of magnetic particles, leading to their enhanced utility properties and sufficient MR performance. This concentrates on the coating of magnetic carbonyl iron (CI) particles with a thin modifying layer as a surface shell utilizing four organosilanes; tetraethoxysilane, (3-aminopropyl)triethoxysilane, bis[3(trimethoxysilyl)propyl]amine and vinyltrimethoxysilane. Characterization of the modified particles and their suspensions was examined using various methods. XPS analysis confirmed the successful particle modification, while the surface free energy was evaluated by tensiometric measurements reflecting the better compatibility of particles with the dispersing medium. The lowest surface free energy possessed particles modified with (3-aminopropyl)triethoxysilane. The magnetization of the modified core-shell particles was not negatively affected by the organosilanes layer present on the particles resulting in comparable MR performance of the systems based on pure CI particles and their modified analogues as was proved by the fitting of the corresponding flow curves by the Robertson-Stiff model. Moreover, the modification of the particles improved their thermo-oxidation stability and chemical stability investigated via thermogravimetric analysis and acidic tests, respectively. Finally, the sedimentation stability of the modified particle-based systems expressed as a weight gain measured using a tensiometer device was enhanced in comparison with the pure CI particle-based system, which can be very positive in the intended applications.
尽管智能材料，特别是磁流变（MR）流体已显示出显著的实际重要性，但其缺点，如磁性填料的聚集、与载液的相容性不足、耐腐蚀性低和沉降稳定性差，仍然严重限制了它们的更广泛应用。为应对这一挑战，我们的研究提出了一种用于磁性颗粒涂层的简便概念，从而提高其使用性能和足够的磁流变性能。这集中于利用四种有机硅烷；四乙氧基硅烷、（3-氨丙基）三乙氧基硅烷、双[3（三甲氧基甲硅烷基）丙基]胺和乙烯基三甲氧基硅烷，在磁性羰基铁（CI）颗粒上涂覆一层薄的改性层作为表面壳。使用各种方法对改性颗粒及其悬浮液进行了表征。XPS分析证实了颗粒改性成功，而通过张力测量评估表面自由能，反映了颗粒与分散介质更好的相容性。用（3-氨丙基）三乙氧基硅烷改性的颗粒具有最低的表面自由能。颗粒上存在的有机硅烷层对改性核壳颗粒的磁化没有负面影响，基于纯CI颗粒及其改性类似物的系统具有可比的磁流变性能，这通过Robertson-Stiff模型对相应流动曲线的拟合得到证明。此外，分别通过热重分析和酸性测试研究表明，颗粒的改性提高了它们的热氧化稳定性和化学稳定性。最后，与基于纯CI颗粒系统相比，基于改性颗粒系统的沉降稳定性（用张力计装置测量的重量增加表示）得到了增强，这在预期应用中可能非常有利。
