Department of Chemistry, The Graduate Center, City University of New York , 365 Fifth Avenue, New York, New York 10016, United States.
Langmuir. 2013 Dec 3;29(48):14779-86. doi: 10.1021/la402597s. Epub 2013 Nov 21.
Iron oxide (Fe3O4) Janus particles assemble into staggered chains parallel to the field lines in an ac electric field. Subsequent application of an external magnetic field leads to contraction of the staggered chains into double chains. The relation between the viscosity of the surrounding solution and the contraction rate of the iron oxide Janus particle chains is studied. Further, the influence of particle size and chain length (i.e., number of particles in chain) on the contraction rate is investigated. The base material for the Janus structure is silica (SiO2) with particle sizes of 1, 2, and 4 μm, and the cap material is Fe3O4. Addition of increasing amounts of glycerol to the aqueous system reveals that the contraction dynamics strongly correlate with the viscosity of the solution. The average chain contraction rate for each particle size can be fitted in the low viscosity range from 1 to 30 mPa·s with a power function of the form A/μ(0.9) - B/μ, in which the coefficients A and B are particle size, electric field, and magnetic-field-dependent constants. Using this function, the viscosity of an unknown solution can be determined, thereby pointing to the potential application of these Janus particle chain assemblies as in situ microviscometers.
氧化铁（Fe3O4）Janus 粒子在交流电场中沿场线平行组装成交错链。随后施加外部磁场会导致交错链收缩成双链。研究了周围溶液的粘度与氧化铁 Janus 粒子链的收缩速率之间的关系。进一步研究了粒径和链长（即链中粒子的数量）对收缩速率的影响。Janus 结构的基体材料是粒径为 1、2 和 4μm 的二氧化硅（SiO2），帽材料为 Fe3O4。向水基体系中添加越来越多的甘油表明，收缩动力学与溶液的粘度密切相关。对于每种粒径，可以在低粘度范围 1 至 30 mPa·s 内用形式为 A/μ(0.9) - B/μ 的幂函数拟合平均链收缩率，其中系数 A 和 B 是与粒径、电场和磁场有关的常数。使用此函数可以确定未知溶液的粘度，从而指出这些 Janus 粒子链组装作为原位微粘度计的潜在应用。
