Measurement of the mean aspect ratio and two characteristic dimensions of polydisperse arbitrary shaped nanoparticles, using translational-rotational ultrafast image-based dynamic light scattering

In this paper, we propose a method to determine the mean value of two characteristic dimensions and the mean aspect ratio of a sample of polydisperse arbitrary shaped nanoparticles named translational-rotational ultrafast image-based dynamic light scattering (TR-UIDLS), which is extended from the ultrafast image-based dynamic light scattering. In TR-UIDLS, rigid arbitrary shaped nanoparticles characterized by two characteristic dimensions, are in Brownian motion in a solvent. They are illuminated by a vertically polarized focused Gaussian beam. A camera records the light scattered by the particles, in vertical-vertical polarization geometry and then in vertical-horizontal polarization geometry. By studying the light fluctuation recorded by the camera in both polarization geometries we can determine the mean values of the translational and rotational diffusion coefficients of the particles in the sample, using a model based on a rod-like/disk-like particle that is equivalent to the particles in the measurement volume during the time between when two consecutive pictures are taken. We have measured a sample of rod-like particles using scanning electron microscopy and compared the dimensions and aspect ratio with those measured using TR-UIDLS. The potential of TR-UIDLS to measure the distributions of translational and rotational diffusion coefficients, aspect ratio, length/thickness, and diameter of a polydisperse sample of nanoparticles is also discussed.