Convection and thermodiffusion of colloidal gold tracers by laser light scattering

Abstract

In a dynamic light scattering experiment, we have investigated the time intensity correlation function and the profile of the transmitted laser beam for organic dispersions of light absorbing colloidal particles containing tiny gold clusters. The correlation functions have been found to show a superposition of an exponential decay, corresponding to Brownian motion of the tracers, and well-defined oscillations. These oscillations are caused by convection due to local heating of the sample by the incident laser beam, which has been confirmed independently via measurements of the local temperature within the sample. It will be shown how the particle convection velocity, which is the order of 1 mm/s, can be obtained quantitatively from the oscillating correlation functions. The profile of the transmitted beam allowed us to determine the Soret coefficient, which is a measure for the thermal diffusion of the particles. This article shows how tracer diffusion, convection, and thermal diffusion can be determined simultaneously by one single experiment, laser light scattering of light absorbing colloidal particles in dispersion.

Crosslinked Spherical Nanoparticles with Core-Shell Topology

“…Both tracer systems have successfully been used to investigate dynamical processes in colloidal dispersions, i.e., self-diffusion, convection, and even thermal diffusion, as has been described in detail elsewhere. [27,29,30] Here, it should be noted that for our gold-doped organosilicon microgels the non-functional shell is used to suppress any negative influence of the gold clusters on the tracer mobility (see above) as well as to control, via its mesh size, the gold cluster morphology by providing a kinetic barrier to diffusion of the gold ions into the reactive core. [28] …”

Time-dependent mode structure for Lyapunov vectors as a collective movement in quasi-one-dimensional systems

“…The autocorrelation functions are accessible experimentally using neutron and light scattering techniques [32,33,34,35]. As an essential aspect of auto-correlation functions is their role as response functions for the system.…”

Thermomagnetic convection of magnetic fluids in a cylindrical geometry

“…Also different convection patterns can be expected with the presence of a vertical temperature gradient. In order to come to a correct statement about the contribution of mass and thermal diffusion to the diffraction patterns in magnetic fluids, spatial temperature measurements and independent measurements of all relevant material parameters as in [12,13] for an organic dispersion are highly desirable. …”

“…An analysis of the physical quantities reveals that both characteristic time scales are several orders of magnitude apart (below and [11]). Direct spatial temperature measurements [12] and independent measurements of all relevant material parameters for organic dispersions [13] showed that the ring pattern is essentially caused by the temperature contribution and not by the concentration contribution.…”