SUPA and School of Physics and Astronomy, University of Edinburgh, King's Buildings, Edinburgh EH9 3FD, UK.
Soft Matter. 2021 Apr 14;17(14):3945-3953. doi: 10.1039/d0sm02255a. Epub 2021 Mar 16.
Particle size is a key variable in understanding the behaviour of the particulate products that underpin much of our modern lives. Typically obtained from suspensions at rest, measuring the particle size under flowing conditions would enable advances for in-line testing during manufacture and high-throughput testing during development. However, samples are often turbid, multiply scattering light and preventing the direct use of common sizing techniques. Differential dynamic microscopy (DDM) is a powerful technique for analysing video microscopy of such samples, measuring diffusion and hence particle size without the need to resolve individual particles while free of substantial user input. However, when applying DDM to a flowing sample, diffusive dynamics are rapidly dominated by flow effects, preventing particle sizing. Here, we develop "flow-DDM", a novel analysis scheme that combines optimised imaging conditions, a drift-velocity correction and modelling of the impact of flow. Flow-DDM allows a decoupling of flow from diffusive motion that facilitates successful particle size measurements at flow speeds an order of magnitude higher than for DDM. We demonstrate the generality of the technique by applying flow-DDM to two separate microscopy methods and flow geometries.
粒径是理解构成我们现代生活基础的颗粒产品行为的关键变量。粒径通常是从静止悬浮液中获得的，如果能够在流动条件下测量粒径，就可以在制造过程中进行在线测试，并在开发过程中进行高通量测试。然而，样品通常是混浊的，会多次散射光线，从而无法直接使用常见的粒径测量技术。差示动态显微镜（DDM）是一种强大的技术，可以对这类样品的视频显微镜进行分析，无需分辨单个颗粒即可测量扩散，从而确定粒径，而且几乎不需要用户输入。然而，当将 DDM 应用于流动样品时，扩散动力学会迅速受到流动效应的控制，从而无法进行粒径测量。在这里，我们开发了“流 DDM”，这是一种新的分析方案，结合了优化的成像条件、漂移速度校正以及对流动影响的建模。流 DDM 可以将流动与扩散运动解耦，从而能够以比 DDM 高一个数量级的流速成功进行粒径测量。我们通过将流 DDM 应用于两种不同的显微镜方法和流动几何形状，证明了该技术的通用性。
