Department of Physics, Institute for Advanced Studies in Basic Sciences, PO Box 45195-1159, Zanjan, Iran.
School of Nano Science, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531, Tehran, 19395, Iran.
Sci Rep. 2020 Feb 17;10(1):2741. doi: 10.1038/s41598-020-59386-5.
We investigate the sedimentation of colloidal micro-spheres and red blood cells (RBCs) in non-Newtonian fluid - silicone oil with different viscosities. We use digital holographic microscopy (DHM) to obtain volumetric information of the sedimenting micro-objects. Especially, the numerical refocusing feature of DHM is used to extract the depth information of multiple particles moving inside the fluid. The effects of proximity to a flat wall and the non-Newtonian behavior on the sedimenting micro-spheres and RBCs are studied by trajectory analyzing and velocimetry. We observe that for lower viscosity values the proximity effect is more pronounced. The variation rate of the particle falling velocities versus their distance to the flat wall decreases by increasing the viscosity of the fluid. For RBCs, however, the decreasing of the velocity variations have a smoother trend. The experimental results verify the theoretical prediction that, similar to Newtonian case, a correction factor in Stokes' law suffices for describing the wall effect.
我们研究了胶体微球和红细胞（RBC）在不同粘度的非牛顿流体-硅油中的沉降。我们使用数字全息显微镜（DHM）来获得沉降微物体的体积信息。特别是，DHM 的数值重聚焦功能被用于提取在流体内部移动的多个粒子的深度信息。通过轨迹分析和速度测量研究了靠近平板壁和非牛顿行为对沉降微球和 RBC 的影响。我们观察到，对于较低的粘度值，接近效应更为明显。随着流体粘度的增加，颗粒下降速度与平板壁距离的变化率减小。然而，对于 RBC，速度变化的减少趋势更为平缓。实验结果验证了理论预测，即类似于牛顿情况，斯托克斯定律中的修正因子足以描述壁效应。
