Fourier correlation microscopy for particle characterization and velocimetry in complex soft matter

Zeta potential measurement is an essential and widely used characterization method of nanometer-sized objects in complex liquids, such as pharmaceuticals, inks, biological material, and proteins. It provides information on stability, affects particle-particle interactions, and plays a crucial role in industrial processes. Over the years, many methodologies have been developed to obtain the zeta potential. Most are based on ensemble measurements, e.g., phase analysis light scattering (PALS), Doppler velocimetry, streaming potentiometry. Particle sizing is another vital characterization parameter and usually goes side-by-side with the zeta potential analysis. In liquids, Dynamic light scattering (DLS) is usually employed when studying small particles, or Laser Diffraction (LD) is used for intermediate to large-sized particles. Both techniques are used extensively and are commercialized and standardized. Both methods are based on ensemble averaging and hence, only measure the average hydrodynamic size of the particle and, to some extent, the distribution of particles. The common problem the above-listed techniques have is that: 1. Detailed information about the size/size distribution is lost because of the underlying averaging process. 2. All light scattering techniques require the samples to be diluted. Therefore, studying the particles within their natural environment in dense solutions may be challenging. Within this project, we will develop a novel particle characterization technique that combines Fourier microscopy and capillary electrophoresis. Electrophoresis is a well-known separation technique in which charged species are separated in an electric field based on charge and size. By Fourier analyzing the video sequence of particles undergoing Brownian motion in the presence of an external electric field, we will extract both the size and the particles' zeta potential as they move through the detection region during the electrophoresis. Because particles have been separated by their electrophoretic mobility in the process, this will allow us to measure the electrophoretic mobility (zeta potential) as a function of particle size with high accuracy. The technique is particularly well-suited for dense solutions of particles ranging in size from 10 nm to 100 micrometers. It outperforms current ensemble methods based on light scattering, such as DLS, LD, or PALS. For the designed particle range, the method will resolve the two main issues common to light scattering techniques mentioned above, providing a better insight into the system under study. The project aims to develop the underlying theory, derive analytical tools, and demonstrate the feasibility of the approach by building a stand-alone sensor device for particle characterization. Additionally, the project will use the principles of the developed microscopy-based velocimetry to study complex liquid matter, including biopharmaceutical aggregation, electroconvection in nematic liquid crystals, and the motion of non-spherical particles in the presence of external fields. The project results will provide novel opportunities and benefits not only to the scientific community but also to the industry.