Measurement of the colloidal particle concentration and size within a drop using the time-shift technique

Abstract

Liquid drops containing particles of nano to micron size are omnipresent in the chemical, pharmaceutical and process industries. In order to optimize such processes, there is a need to characterize these drops in terms of size and colloidal particle concentration. This study is devoted to estimating the colloidal nanoparticle concentration within such drops by using the time-shift technique. The estimation is achieved using two different approaches. The first utilizes the signal strength generated by light scattering from the particles in the drop relative to reflective scattering from the undisturbed drop surface. The second approach monitors the attenuation of the portion of the time-shift signal generated by second-order refractive scattering, i.e. light which has passed twice through the drop. These methods have been simulated using previously developed light scattering codes based on Monte Carlo ray tracing. Corresponding experiments have been implemented to validate these two estimation methods. For this, colloidal drops were generated by mixing water with the polystyrene latex nanoparticles and varying the volume concentration. Good agreement between the experimental and simulation results has been achieved, indicating that the time-shift technique can be further developed to meet this measurement task.