Diffusion configuration of water molecules in diffusion weighted imaging

In the studying of fibers microstructure of brain white matter, many reconstruction methods have been proposed to interpret the diffusion-weighted signal. Those methods can be categorized into model-based and model-free methods. In this paper, the diffusion configuration of water molecules are discussed, and two questions are put forward to analyze the performance of the current algorithms about diffusion configuration. The first question is what the diffusion profile looks like in voxel? The second question is what is the location of fibers in a voxel? As a result, firstly, most of model-based algorithms ignore much information coming from the isotropic diffusion, which will lead to an inaccurate estimation. Secondly, model-free algorithms just provide direction information of fibers, ignore or cannot provide location information of fibers. So unfortunately, neither model-based methods nor model-free methods can resolve those two questions very well. How to resolve those questions is still an open problem, and it may be an interesting direction in the future research.     

Diffusion of water in additively colored potassium iodide crystals

The diffusion of water into additively colored potassium iodide has been studied in the range 15–45°C. Penetration depths, measured by decrease in the F-band absorption, increase with $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The diffusion coefficient, D = 0·58 exp (?6496/T) cm² sec^?1 agrees very well with that determined by other workers. The Henry's law constant, $\text{K =}\text{C}{}_0\text{p}{}_{\mathrm{w}}\text{= 1·3 × 10}{}^9\text{exp}\text{(+4882/T)}\text{cm}{}^{\mathrm{?3}}\text{torr}{}^{\mathrm{?1}}$ implies a water concentration of C₀ ? 10¹⁷ molecules per cm³ in the surface of KI crystals in equilibrium with an environment at 25°C and 35 per cent relative humidity. The large C₀ makes penetration very rapid. Diffusion occurs by interstitial migration of water molecules with an entropy of activation of 9.4 cal/mol deg and an enthalpy of activation of 12·9 kcal/mol.     

Diffusion kinetics of water molecules in a nanoporous adsorbent

The diffusion of water vapor into porous polymer adsorbent MN-200 has been investigated by diode laser spectroscopy with a time resolution of 0.1 s. The cascade character of diffusion, caused presumably by the fractality of the porous matrix space, is established by decomposition analysis. The collisionless (Knudsen) mode of water motion in pores, in which water molecules can be sorted according to their spin states, is selected.     

Diffusion coefficient and shear viscosity of rigid water models

We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC/E with three sites, and TIP4P/2005 with four sites) and a polarizable one (Dang-Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also provides an estimate of the viscosity of all water models, which we compare to the Green-Kubo result. In all cases, a good agreement is found. The TIP4P/2005 model is in better agreement with the experimental data for both diffusion and viscosity. The SPC/E and Dang-Chang models overestimate the diffusion coefficient and underestimate the viscosity.     

Diffusion anisotropy in a toroidal (ring) vortex in water

Diffusion of paint (ink) particles in a toroidal (ring) vortex in a density-homogeneous liquid (water) was experimentally studied. Particle diffusion anisotropy in rotating water of the vortex was detected. The effect consists in the fact that the particle diffusivity in the direction perpendicular to the rotation axis of the torus core is much lower than that in the direction parallel to the rotation axis.     

Diffusion of water in nano-porous polyamide membranes: Quasielastic neutron scattering study

Dynamics of water sorbed in a reverse osmosis polyamide membrane (ROPM) as studied by quasielastic neutron scattering (QENS) is reported here. The trimesoylchloride-m-phenylene diamine based ROPM is synthesized by interfacial polymerization technique. QENS data indicates that translational motion of water confined in ROPM gets modified compared to bulk water whereas rotational motion remains unaltered. Translational motion of water in ROPM is found to follow random jump diffusion with lower diffusivity compared to bulk water. Translational diffusivity does not show the Arrhenius behaviour.     

Ostwald ripening in rarefied systems

Mass exchange between spherical molecular clusters is analyzed in the case when the mean free path of molecules in the intercluster space is much larger than the cluster sizes but much smaller than average intercluster separation. It is shown that there is a steady-state regime when big clusters grow at the expense of the smaller ones (Ostwald ripening), which is characterized by a one-parametric family of self-similar cluster size distribution functions and by an exponentially growing average cluster size. The obtained self-similar cluster size distributions are entirely different from those given by the classical theory of Ostwald ripening. Implications of the obtained results are discussed.     

The theory of Ostwald ripening

Developments in the theory of Ostwald ripening since the classic work of I. M. Lifshitz and V. V. Slyozov (LS) are reviewed and directions for future work are suggested. Recent theoretical work on the role of a finite volume fraction of coarsening phase on the ripening behavior of two-phase systems is reformulated in terms of a consistent set of notation through which each of the theories can be compared and contrasted. Although more theoretical work is necessary, these theories are in general agreement on the effects of a finite volume fraction of coarsening phase on the coarsening behavior of two-phase systems. New work on transient Ostwald ripening is presented which illustrates the broad range of behavior which is possible in this regime. The conditions responsible for the presence of the asymptotic state first discovered by LS, as well as the manner in which this state is approached, are also discussed. The role of elastic fields during Ostwald ripening in solid-solid mixtures is reviewed, and it is shown that these fields can play a dominant role in determining the coarsening behavior of a solid-solid system.     

Ostwald ripening of beta-carotene nanoparticles

Ostwald ripening, the interfacial-energy-driven dissolution and reprecipitation of solutes, becomes an increasingly significant problem for nanoparticle formulations. We present the first quantitative study of Ostwald ripening for nanoparticle dispersions. The Lifshitz-Slyozov-Wagner (LSW) theory of particle growth driven by diffusion is applied to study beta-carotene nanoparticles with sizes of O(100 nm) formed by our block-copolymer protected Flash Nanoprecipitation process. A numerical implementation of the LSW theory that accounts for the original particle size distribution is presented. The predicted particle sizes from the numerical simulation are compared with the experimental results measured by dynamical light scattering. The results show quantitative agreement with no adjustable parameters. The addition of antisolvent results in the reduction of the ripening rate by dramatically decreasing bulk solubility.     

Diffusional mechanism of strong selection in ostwald ripening

The purpose of this paper is to show through a systematic asymptotic analysis that fluctuations, accounted for as a diffusional perturbation in the Lifshitz-Slyozov-Wagner (LSW) model of Ostwald ripening, provides, as conjectured previously by Meerson [Phys. Rev. E 60, 3072 (1999)], a "strong" selection of the limiting solution, out of a one-parameter family of similarity solutions with a finite support, as the sole attractor of time evolution. Throughout the latter, the previously described weak selection of other similarity solutions of that family, by the initial conditions with finite supports, occurs as intermediate time asymptotics. The respective mechanism is traced first for a simple instance of the LSW model with linear characteristic equations (integer power in the particle growth rate law equals -1), beginning with the analysis of steady states in the perturbed problem in similarity variables and weak selection in the unperturbed problem, followed by a detailed asymptotic analysis of the time-dependent perturbed problem, and generalized next for an arbitrary integer power in the range [-1,2]. The approximate asymptotic solutions obtained are compared with the exact numerical ones.     

Fluctuations provide strong selection in Ostwald ripening

A selection problem that appears in the Lifshitz-Slyozov (LS) theory of Ostwald ripening is reexamined. The problem concerns selection of a self-similar distribution function (DF) of the minority domains with respect to their sizes from a whole one-parameter family of solutions. A strong selection rule is found via an account of fluctuations. Fluctuations produce an infinite tail in the DF and drive the DF towards the "limiting solution" of LS or its analogs for other growth mechanisms.     

Age-related changes of anisotropic properties of water self-diffusion in human lens: Diffusion anisotropy in lens with aging

Water self-diffusion in human lenses of different age is studied. It is shown that there is a strong anisotropy of self-diffusion of water molecules in old lenses, whereas in young lenses such anisotropy does not occur. This anisotropy appears between 20 and 50 years and is probably connected with the flatness of lens fibers with aging.     

Diffusion in multi-component polymeric systems: Diffusion of non-volatile species in thin films

Polymeric films for high-tech products like LCD-panels, transdermal patches or medical test strips typically consist of a polymer and one or more non-volatile additives. If during the production process a multi-component solution is coated and subsequently dried, the diffusion of solvents and non-volatile species in the polymeric systems plays an important role. Recent experiments revealed that the drying conditions can have a significant influence on the formation of inhomogeneous distribution of the non-volatile components in the final foil and therefore affects desired product properties. The distribution of the non-volatile components in the final film has an important impact on the physical and chemical properties, including mechanical and optical properties, wetting behavior or drug release rates i.e. the product quality of the polymeric system. To be able to describe the diffusion of non-volatile species in a multi-component polymeric system during drying correctly, reliable information about the influence of the solvent concentration on the mobility of the additive are essential. To obtain information about the mobility of the additive in the polymeric solution new experiments were performed and observed by means of Inverse-Micro-Raman-Spectroscopy (IMRS). By fitting simulated concentration profiles to the experimental data, the temperature and concentration dependent diffusion coefficient of the non-volatile additive in the polymer solution was determined. The investigations are part of a bilateral funding of NFG in the US and DFG in Germany. Diffusion of volatile species in multicomponent polymeric systems are investigated by the group of Richard Cairncross.