Self-diffusion

Using the transient hot wire and pulsed field gradient nuclear magnetic resonance methods we determined the thermal conductivity and the solvent self-diffusion coefficient (SDC) in aqueous suspensions of quasi-monodisperse spherical silica nanoparticles. The thermal conductivity was found to increase at higher volume fraction of nanoparticles in accordance with the effective medium theory albeit with a smaller slope. On the other hand, the SDC was found to decrease with nanoparticle volume fraction faster than predicted by the effective medium theory. These deviations can be explained by the presence of an interfacial heat-transfer resistance and water retention by the nanoparticles, respectively. We found no evidence for anomalous enhancement in the transport properties of nanofluids reported earlier by other groups.

Starting from some fundamentals of solid-state diffusion, we remind the reader to the major techniques for lattice diffusion measurements. Self-diffusion is the most basic diffusion phenomenon in any solid. The paper covers main features of self-diffusion in pure fcc and bcc metals and some important facts about diffusion of substitutional solutes in metals. Binary intermetallics are compounds of two metals or of a metal and a semimetal. Their structures are different from those of the constituents. Some intermetallics are interesting functional materials others have attracted attention as high-temperature structural materials. The paper reviews some results mainly from our laboratory on diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si and Co-Nb, which have been published in detail elsewhere. Some results for the ternary system Ni-Fe-Al are also mentioned.

Deformation of ductile crystalline-amorphous nanolaminates is not well understood due to the complex interplay of interface mechanics, shear banding, and deformation-driven chemical mixing. Here we present indentation experiments on 10 nm nanocrystalline Cu–100 nm amorphous CuZr model multilayers to study these mechanisms down to the atomic scale. By using correlative atom probe tomography and transmission electron microscopy we find that crystallographic slip bands in the Cu layers coincide with noncrystallographic shear bands in the amorphous CuZr layers. Dislocations from the crystalline layers drag Cu atoms across the interface into the CuZr layers. Also, crystalline Cu blocks are sheared into the CuZr layers. In these sheared and thus Cu enriched zones the initially amorphous CuZr layer is rendered into an amorphous plus crystalline nanocomposite.

Exchange data from a range of mixed conducting perovskites is reviewed. It is noted that the surface exchange coefficient and the self-diffusion coefficient are related, which in turn implies that the vacancy concentration of the material plays an important role in determining the magnitude of the former. On the assumption that the surface vacancy is the site at which exchange

3D Shape matching is an important problem in computer vision. One of the major difficulties in finding dense correspondences between 3D shapes is related to the topological discrepancies that often arise due to complex kinematic motions. In this paper we propose a shape matching method that is robust to such changes in topology. The algorithm starts from a sparse set of seed matches and outputs dense matching. We propose to use a shape descriptor based on properties of the heat-kernel and which provides an intrinsic scale-space representation. This descriptor incorporates (i) heat-flow from already matched points and (ii) self diffusion. At small scales the descriptor behaves locally and hence it is robust to global changes in topology. Therefore, it can be used to build a vertex-to-vertex matching score conditioned by an initial correspondence set. This score is then used to iteratively add new correspondences based on a novel seed-growing method that iteratively propagates the seed correspondences to nearby vertices. The matching is farther densified via an EM-like method that explores the congruency between the two shape embeddings. Our method is compared with two recently proposed algorithms and we show that we can deal with substantial topological differences between the two shapes.

Synthetic and natural smectite clays, with different structural and physical parameters, were tested as nanofillers for the creation of Nafion nanocomposites. The solution intercalation method has been successfully applied for incorporation of layered materials into the polymer, while the effect of the solvent, temperature and filler loading were examined in order to determine the optimum conditions for the preparation of highly homogeneous composites.NMR methods, including pulsed-field-gradient spin-echo (PFGSE) and spin-lattice relaxation time (T1) were used to investigate behavior of water confined in recast Nafion and in Nafion–clay hybrids membranes.The transport mechanism appears to be influenced from the dimensions of the dispersed platelets and mainly from the type of nanocomposites formed upon mixing the clay particles with the polymer matrix. Compared to pure Nafion, the water uptake and the water diffusion of the hybrid membranes are increased, with the exception of the Kunipia-Nafion composite. A remarkable behaviour at high temperature is observed, where composite membranes maintain stable and unwavering diffusion for many hours and in conditions of not humidification, proving the exceptional water retention property of these materials. Finally the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion, hence both these characteristics are highly desirable for use in fuel cell applications.► Three smectite clays were tested as nanofillers to create Nafion hybrid membranes. ► Conventional and exfoliated nanocomposites are created depending on the clay. ► Dynamic behavior study of water were conducted by NMR (self-diffusion and T1). ► Noteworthy water retention at high T of composites based on Laponite and SWy-2. ► Effects of filler loading and of solvent on the performance of the nanocomposites.

ABSTRACT The diaphragm cell method (DCM) was applied to determine the self-diffusion of glucose in cell culture media (CCM) and water (reference fluid). For this purpose, a diffusion cell based on the DCM principle was constructed and the cell was calibrated with ethanol prior to carrying out the diffusion experiments. The results show that the diffusion coefficients of glucose in CCM are significantly smaller as compared to those for water which are due to the larger dynamic viscosity of CCM. This may also account for the presence of extra components and difference in fluid properties of CCM. The diffusivity values obtained from the present study are compared to values estimated from Stokes-Einstein equation and it appears that the agreement is fairly good.