Multiple particle tracking microrheology (MPT) is a powerful tool for quantitatively characterizing rheological properties of soft matter. Traditionally, MPT uses a single particle size to characterize rheological properties. But in complex systems, MPT measurements with a single size particle can characterize distinct properties that are linked to the materials' length scale dependent structure. By varying the size of probes, MPT can measure the properties associated with different length scales within a material. We develop a technique to simultaneously track a bi-disperse population of probe particles. 0.5 and 2 μm particles are embedded in the same sample and these particle populations are tracked separately using a brightness-based squared radius of gyration, R_g². Bi-disperse MPT is validated by measuring the viscosity of glycerol samples at varying concentrations. Bi-disperse MPT measurements agree well with literature values. This technique then characterizes a homogeneous poly(ethylene glycol)-acrylate:poly(ethylene glycol)-dithiol gelation. The critical relaxation exponent and critical gelation time are consistent and agree with previous measurements using a single particle. Finally, degradation of a heterogeneous hydrogenated castor oil colloidal gel is characterized. The two particle sizes measure a different value of the critical relaxation exponent, indicating that they are probing different structures. Analysis of material heterogeneity shows measured heterogeneity is dependent on probe size indicating that each particle is measuring rheological evolution of a length scale dependent structure. Overall, bi-disperse MPT increases the amount of information gained in a single measurement, enabling more complete characterization of complex systems that range from consumer care products to biological materials.

中文翻译：

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使用双分散探针直径测量的多粒子跟踪微流变学†

多重粒子跟踪微流变学（MPT）是定量表征软质流变特性的强大工具。传统上，MPT使用单一粒径表征流变性能。但是在复杂的系统中，用单个尺寸的颗粒进行的MPT测量可以表征与材料的长度标度相关的结构相关的不同属性。通过改变探针的尺寸，MPT可以测量与材料内不同长度刻度相关的特性。我们开发了一种技术，可以同时跟踪探针颗粒的双分散种群。将0.5和2μm粒子嵌入同一样品中，并使用基于亮度的平方回转半径R _g ²分别跟踪这些粒子的数量。通过测量不同浓度的甘油样品的粘度来验证双分散MPT。双分散MPT测量值与文献值非常吻合。然后，该技术表征了均相的聚（乙二醇）-丙烯酸酯：聚（乙二醇）-二硫醇凝胶化。临界弛豫指数和临界胶凝时间是一致的，并且与先前使用单个颗粒的测量结果一致。最后，表征了非均质氢化蓖麻油胶体凝胶的降解。两种粒径测量的临界弛豫指数值不同，表明它们在探测不同的结构。对材料异质性的分析表明，测得的异质性取决于探针的尺寸，表明每个颗粒都在测量与长度成比例关系的结构的流变演化。