Use of dynamic schlieren interferometry to study fluctuations during free diffusion.
TL;DR: A form of schlieren interferometry is used to measure the mean-squared amplitude and temporal autocorrelation function of concentration fluctuations driven by the presence of a gradient during the free diffusion of a urea solution into water.
Abstract: We used a form of schlieren interferometry to measure the mean-squared amplitude and temporal autocorrelation function of concentration fluctuations driven by the presence of a gradient during the free diffusion of a urea solution into water. By taking and processing sequences of images separated in time by less than the shortest correlation time of interest, we were able to simultaneously measure dynamics at a number of different wave vectors. The technique is conceptually similar to the shadowgraph method, which has been used to make similar measurements, but the schlieren method has the advantage that the transfer function is wave-vector independent rather than oscillatory.
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TL;DR: In this article, the Soret and diffusion coefficients of a binary mixture undergoing thermodiffusion were analyzed using a double-frame differential analysis of the acquired images, and the static power spectrum and the dynamics of non-equilibrium fluctuations were obtained.
20 citations
TL;DR: It is shown that dark field differential dynamic microscopy is the ideal tool for probing the roto-translational Brownian motion of anisotropic shaped particles in aqueous dispersions of non-motile bacteria and of colloidal aggregates of spherical particles.
Abstract: Micro- and nanoscale objects with anisotropic shape are key components of a variety of biological systems and inert complex materials, and represent fundamental building blocks of novel self-assembly strategies. The time scale of their thermal motion is set by their translational and rotational diffusion coefficients, whose measurement may become difficult for relatively large particles with small optical contrast. Here we show that dark field differential dynamic microscopy is the ideal tool for probing the roto-translational Brownian motion of anisotropic shaped particles. We demonstrate our approach by successful application to aqueous dispersions of non-motile bacteria and of colloidal aggregates of spherical particles.
20 citations
TL;DR: It is found that the correlation time versus wavenumber for gold nanocolloids is concave shaped, whereas, for silica colloids, it is convex shaped, and the difference in correlation time behavior is not only due to the size of the particle, but also to possible plasmonic interactions in gold colloids.
Abstract: We report quantitative experimental results regarding concentration fluctuations based on a small-angle light-scattering setup. A shadowgraph technique was used to record concentration fluctuations in a free-diffusion cell filled with colloids. Our experimental setup includes an objective attached to the CCD camera to increase the field of view. We performed two separate experiments, one with 20 nm gold and the other with 200 nm silica colloids, and extracted both the structure factors and the correlation time during the early stages of concentration fluctuations. The temporal evolution of fluctuations was also qualitatively investigated using recursive plots and spatial-temporal sections of fluctuating images. We found that the correlation time versus wavenumber for gold nanocolloids is concave shaped, whereas, for silica colloids, it is convex shaped. The difference in correlation time behavior is not only due to the size of the particle, but also to possible plasmonic interactions in gold colloids.
19 citations
TL;DR: A simplified expression for the relative amplitude of the two mass diffusion modes is obtained, allowing a parameterized determination of polystyrene and toluene Soret coefficients in the ternary mixture, suggesting that a two wavelength shadowgraph experiment is needed for a complete determination of all the coefficients.
Abstract: Dynamic analysis of the light scattered by non-equilibrium fluctuations in a thermodiffusion experiment has been performed on a sample of polystyrene-toluene-n -hexane, at 0.9-49.55-49.55% mass fraction. Time decays of the non-equilibrium fluctuations have been obtained revealing the accurate detectability of three modes. The slowest mode has been attributed to the mass diffusion of the polymer into the binary solvent; the intermediate one to mass diffusion of the two molecular components of the solvent; finally, the fastest one has been attributed to the thermal diffusivity of the overall mixture. The two eigenvalues of the mass diffusion matrix have been evaluated with accuracy in the order of 1%. Neglecting cross-diffusion effects we obtain a simplified expression for the relative amplitude of the two mass diffusion modes, allowing a parameterized determination of polystyrene and toluene Soret coefficients in the ternary mixture. We suggest that a two wavelength shadowgraph experiment is needed for a complete determination of all the coefficients.
18 citations
TL;DR: In this article, the authors show that dark field differential dynamic microscopy is the ideal tool for probing the roto-translational Brownian motion of shape anisotropic particles and demonstrate their approach by successful application to aqueous dispersions of nonmotile bacteria and of colloidal aggregates of spherical particles.
Abstract: Micro- and nanoscale objects with anisotropic shape are key components of a variety of biological systems and inert complex materials, and represent fundamental building blocks of novel self-assembly strategies. The time scale of their thermal motion is set by their translational and rotational diffusion coefficients, whose measurement may become difficult for relatively large particles with small optical contrast. Here we show that Dark Field Differential Dynamic Microscopy is the ideal tool for probing the roto-translational Brownian motion of shape anisotropic particles. We demonstrate our approach by successful application to aqueous dispersions of non-motile bacteria and of colloidal aggregates of spherical particles.
18 citations
References
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Book•
01 Jan 1973TL;DR: CRC handbook of chemistry and physics, CRC Handbook of Chemistry and Physics, CRC handbook as discussed by the authors, CRC Handbook for Chemistry and Physiology, CRC Handbook for Physics,
Abstract: CRC handbook of chemistry and physics , CRC handbook of chemistry and physics , کتابخانه مرکزی دانشگاه علوم پزشکی تهران
52,268 citations
Book•
05 Feb 1976
TL;DR: In this paper, a comprehensive introduction to principles underlying laser light scattering focuses on time dependence of fluctuations in fluid systems and provides an introduction to theory of time correlation functions, with chapters on projection operator techniques in statistical mechanics.
Abstract: This comprehensive introduction to principles underlying laser light scattering focuses on time dependence of fluctuations in fluid systems It also serves as introduction to theory of time correlation functions, with chapters on projection operator techniques in statistical mechanics Over 60 text figures 1976 edition
2,488 citations
Journal Article•
1,037 citations
TL;DR: The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell, suggesting that the chaotic behavior is intrinsic to large aspect ratio geometries.
Abstract: We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The fluid had a Prandtl number [sigma][approx]1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries.
222 citations
TL;DR: In this article, a multi-tau software correlator was used to measure dynamic light scattering at many angles simultaneously, from 0.07° to 5.1°, in order to cover the wide spectrum of decay times associated with the large range of accessible angles, where the correlator channel spacing is quasilogarithmic rather than linear.
Abstract: We use a charge coupled device (CCD) camera and a multi-tau software correlator to measure dynamic light scattering (DLS) at many angles simultaneously, from 0.07° to 5.1°. Real-time autocorrelation functions are calculated by averaging both over time and over CCD pixels, each corresponding to a different coherence area. In order to cover the wide spectrum of decay times associated with the large range of accessible angles, we adopt the multitau scheme, where the correlator channel spacing is quasilogarithmic rather than linear. A detailed analysis is presented of the effects of dark noise, stray light, and finite pixel area, and methods to correct the data for these effects are developed, making a CCD camera a viable alternative for a DLS detector. We test the apparatus on a dilute suspension of colloidal particles. Very good agreement is found between the particle radius derived from the CCD data, and that obtained with a conventional DLS setup.
187 citations
"Use of dynamic schlieren interferom..." refers background in this paper
...(3) to the data with S0 and qc as adjustable parameters....
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...(3), which indicates that this quantity depends on the concentration difference and not on the gradient....
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