Electro-optical Study of the Anomalous Rotational Diffusion in Polymer Solutions

Abstract

Brownian diffusion of spherical nanoparticles is usually exploited to ascertain the rheological properties of complex media. However, the behavior of the tracer particles is affected by a number of phenomena linked to the interplay between the dynamics of the particles and polymer coils. For this reason, the characteristic lengths of the dispersed entities, depletion phenomena, and the presence of sticking conditions have been observed to affect the translational diffusion of the probes. On the other hand, the retardation effect of the host fluid on the rotational diffusion of nonspherical particles is less understood. We explore the possibility of studying this phenomenon by analyzing the electro-orientation of the particles in different scenarios in which we vary the ratio between the particle and polymer characteristic size, and the geometry of the particles, including both elongated and oblate shapes. We find that the Stokes–Einstein relation only applies if the radius of gyration of the polymer is much shorter than the particle size and when some repulsive interaction between both is present.

In situ pulmonary mucus hydration assay using rotational and translational diffusion of gold nanorods with polarization-sensitive optical coherence tomography

“…Traditionally, the diffusion of nanoparticles is measured using dynamic light scattering (DLS). GNRs have been assessed via DLS and found to have predictable rotational and translational diffusion rates in water and aqueous glycerol solutions, 28 , 29 and diffusion of GNRs or related rod-like particles have been proposed for material characterization of polymer solutions 30 , 31 . However, none of these studies have exploited the plasmonic resonance of GNRs to increase detectability within optically dense materials.…”

“…GNRs have been assessed via DLS and found to have predictable rotational and translational diffusion rates in water and aqueous glycerol solutions, 28 , 29 and diffusion of GNRs or related rod-like particles have been proposed for material characterization of polymer solutions. 30 , 31 However, none of these studies have exploited the plasmonic resonance of GNRs to increase detectability within optically dense materials. Furthermore, an imaging platform such as optical coherence tomography (OCT) is particularly advantageous for performing depth-resolved DLS in biomaterials due to its increased depth penetration and small sample volume requirement.…”