Search results for "Diffusion"
showing 10 items of 1615 documents
A New Colloid Model for Dissipative-Particle-Dynamics Simulations
2016
We propose a new model to simulate spherical colloids. This is a mesoscopic method based on the dissipative particle dynamics. The colloid is represented by a large spherical bead, and its surface interacts with the solvent beads through a pair of dissipative and stochastic forces. This new model extends the tunable-slip boundary condition [Eur. Phys. J. E 26, 115 (2008)] from planar surfaces to curved geometry, thus allows one to study colloids with slippery surfaces. Simulation results show good agreement with the prediction of hydrodynamic theories, indicating the hydrodynamic interactions are properly accounted in our new model.
Thermal diffusion and Soret feedback of gold-doped polyorganosiloxane nanospheres in toluene
2000
We have investigated diffusion and thermal diffusion properties of light-absorbing colloidal polyorganosiloxane microgels containing tiny nanometer-sized gold clusters dispersed in toluene. Transient holographic gratings allow for very subtle perturbations in the linear regime where Soret feedback is negligible. Gold-doped colloids of different size and crosslink ratios show different Soret coefficients but identical thermal diffusion coefficients D(T). Undoped colloids tend to aggregate, but a consistent interpretation is obtained if an identical D(T) is assumed for the doped, the undoped, and the aggregated particles. Previously reported Soret feedback measurements on similar systems inci…
Relation of Interdiffusion and Self-Diffusion in Polymer Mixtures
1986
From different assumptions one obtains linear relationships either between the interdiffusion coefficient and the self-diffusion coefficients or between the inverse interdiffusion coefficient and the inverse self-diffusion coefficients. The nature of these assumptions and possible experiments for discriminating between them are discussed.
Nonexponential 2H spin-lattice relaxation as a signature of the glassy state
1990
Abstract High-precision measurements of 2H spin-lattice relaxation on several molecular glass-forming liquids have been performed. As a general feature the following can be stated: At temperatures more than ten to twenty degrees above the calorimetric glass transition temperature Tg the 2H spin-lattice relaxation is exponential; below that temperature regime the relaxation is nonexponential. This crossover from exponential to nonexponential magnetization recovery implies that no common spin temperature caused by spin diffusion exists in a 2H glass. This contrasts 1H spin-lattice relaxation which is found to be strictly monoexponential throughout. The occurrence of nonexponential 2H relaxati…
Testing Mode-Coupling Theory for a Supercooled Binary Lennard-Jones Mixture I: The van Hove Correlation Function
1995
We report the results of a large scale computer simulation of a binary supercooled Lennard-Jones liquid. We find that at low temperatures the curves for the mean squared displacement of a tagged particle for different temperatures fall onto a master curve when they are plotted versus rescaled time $tD(T)$, where $D(T)$ is the diffusion constant. The time range for which these curves follow the master curve is identified with the $\alpha$-relaxation regime of mode-coupling theory (MCT). This master curve is fitted well by a functional form suggested by MCT. In accordance with idealized MCT, $D(T)$ shows a power-law behavior at low temperatures. The critical temperature of this power-law is t…
Charge transport in electrically responsive polymer layers
2007
The processes of charge transport in the conducting polymer electrochromic films have been studied by means of spectral-electrochemical method, impedance spectroscopy and cyclic voltametry measurements. It has been shown that charge transport during the coloration-bleaching processes is not symmetric phenomenon. By means of impedance spectroscopy the effective diffusion coefficients for anode and cathode charge transport have been measured. The higher rate of charge transport in the bleaching process as compared to coloration is considered in the frame of conformation rebuilding of conducting polymer chains.
Tuning Of Organic Heterojunction Conductivity By The Substituents' Electronic Effects In Phthalocyanines For Ambipolar Gas Sensors
2021
Abstract Exploiting organic heterojunction effects in electrical devices are an important strategy to improve the electrical conductivity, which can be utilized into improving the conductometric gas sensors performances. In this endeavor, the present article reports fabrication of organic heterostructures in a bilayer device configuration incorporating octa-substituted nickel phthalocyanines (NiPc) and radical lutetium bis-phthalocyanine (LuPc2) and investigates their sensing properties towards NH3 vapor. NiPc having hexyl sulfanyl, hexyl sulfonyl and p-carboxyphenoxy moieties are synthesized, which electronic effects are electron donating, accepting and moderate accepting, respectively, al…
Bis(2-ethylhexyl)phosphoric acid/bis(2-ethylhexyl)amine mixtures as solvent media for lithium-ions: A dynamical study
2016
Abstract The self-diffusion coefficient, the spin-lattice relaxation times and ionic conductivity of lithium ions in liquid mixtures composed of bis(2-ethylhexyl)amine (BEEA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) have been thoroughly investigated as a function of composition and temperature by NMR spectroscopy and conductometry. While the temperature and composition dependence of diffusion coefficients of lithium ions follow the same trend observed for those of the surfactant molecules, the spin-lattice relaxation times of lithium ions and 1 H are remarkably different. The observed behavior has been interpreted in terms of lithium ions diffusion occurring through its association with…
Protofibril formation of amyloid beta-protein at low pH via a non-cooperative elongation mechanism.
2005
Deposition of the amyloid beta-protein (Abeta) in senile or diffuse plaques is a distinctive feature of Alzheimer's disease. The role of Abeta aggregates in the etiology of the disease is still controversial. The formation of linear aggregates, known as amyloid fibrils, has been proposed as the onset and the cause of pathological deposition. Yet, recent findings suggest that a more crucial role is played by prefibrillar oligomeric assemblies of Abeta that are highly toxic in the extracellular environment. In the present work, the mechanism of protofibril formation is studied at pH 3.1, starting from a solution of oligomeric precursors. By combining static light scattering and photon correla…
Practical Applications of Models of Oxygen Supply, Diffusion, and Consumption
1996
It is the objective of this paper to describe, what models of oxygen supply, diffusion, and consumption have been and can be used for and to discuss some common problems in employing mathematical models of O2 transport. In a first part, four typical fields for model applications are selected from the wide variety of former investigations and are illustrated with some recent examples.