Traditional bead-spring models of the polymer dynamics are based on the Einstein theory of the Brownian motion (BM), valid only at the times much larger than the particle´s relaxation time. The reason is in neglecting the inertial and memory effects in the dynamics. In the present work we use a generalized theory of the BM to build models of the dynamics of flexible polymers in dilute solution. The equations of motion for the polymer segments include the friction force that follows from the linearized Navier-Stokes hydrodynamics. It has a form of a memory integral. To get a correct description of the short-time dynamics, inertial effects are included into the consideration. For negligible hydrodynamic interactions (HI) between the beads the motion of the polymer center of mass is not influenced by internal forces within the chain and has been considered exactly. Then we include the HI int the description of motion of chains, which are assumed Gaussian in equilibrium. Analytical solutions for the observable time correlation functions describing the movement of the polymer coils significantly differ from the classical results showing, in particular, algebraic long-time tails and ballistic motion at short times.

The present paper involves application of nondestructive radioactive tracer technique in characterization of Dowex 550A LC and Indion-820 anion exchange resins. The characterization study was based on kinetic of exchange reactions between inactive iodide/bromide ions on the resins with radioactive iodide/bromide ions in the solution. During iodide exchange reaction performed at a constant temperature of 40.00C, using 1.000 g of ion exchange resins and labeled iodide ion solution of concentration 0.003 mol/L, for Dowex 550A LC resin the specific reaction rate and initial rate of ion exchange was 0.271 min-1 and 0.141 mmol/min respectively, while the amount of iodide ions exchanged was 0.522 mmol, and log Kd was calculated to be 12.1. The above values calculated for Dowex 550A LC resin was higher than the respective values of 0.108, 0.330, 0.036 and 6.0 as obtained for Indion-820 resins. Similar results were obtained for the two resins during bromide exchange reactions, thereby indicating superior performance of Dowex 550A LC resin over Indion-820 resins.

The estimation of axon radius provides insights into brain function [1] and could provide progression and classification biomarkers for a number of white matter diseases [2-4]. A recent in silico study [5] has shown that optimised gradient waveforms (GEN) and oscillating gradient waveform spin echo (OGSE) have increased sensitivity to small axon radius compared to pulsed gradient spin echo (PGSE) diffusion MR sequences. In a follow-up study [6], experiments with glass capillaries show the practical feasibility of GEN sequences and verify improved pore-size estimates. Here, we compare PGSE with sine, sine with arbitrary phase, and square wave OGSE (SNOGSE, SPOGSE, SWOGSE, respectively) for axon radius mapping in the corpus callosum of a rat, ex-vivo. Our results suggest improvements in pore size estimates from OGSE over PGSE, with greatest improvement from SWOGSE, supporting theoretical results from [5] and other studies [7-9].

Magnetic resonance imaging was used to study swelling dynamics and hydrogel formation of xanthan tablets with or without Pentoxifylline drug in water and HCl pH 1.2 media at two different ionic strengths. Significant changes were observed only in the erosion front positions leading to different hydrogel thicknesses. The impact of the drug on the hydrogel thickness was found to be dependent on the medium conditions at high enough drug amount. The drug does not change the hydrogel thickness in water medium, whereas in acid medium the presence of the drug results in thinner hydrogel. The increased ionic strength in water medium also leads to formation of the thinner hydrogel layer in tablets with high enough drug content, while the effect of NaCl in HCl pH 1.2 medium is very small.

The results of one- and two-dimensional 1H nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusometry studies of water in white cement paste with a water-tocement ratio 0.4 and aged from 1 day to 1 year are reported. The study shows that the NMRPFG method is primarily sensitive to the capillary porosity. Data is fit on the basis of a lognormal pore size distribution with pore size dependent relaxation times. The volume mean capillary pore size is 4.2 μm in mature paste, similar to 1 week suggesting that hydrates and gel porosity do not form in the capillary porosity once the latter has been substantially created. No evidence is found of capillary pore anisotropy in cement paste.

It would be very beneficial to perform MRI of fluids and sense the fluid pressure changes. Our aim is to demonstrate a contrast agent capable of MR sensitivity to sub-atmospheric pressure changes. To achieve this, monodisperse microbubbles were prepared with an optically measured mean radius of 1.4 ± 0.8 μm. A repeated pressure change cycle was applied on the microbubble contrast agent, until it produced an MR signal change solely due to the bubble radius change. The bubbles’ contribution to the relaxation rate before and after applying sub-atmospheric pressure changes was estimated and its echo time dependence modelled, so as to inform the mean radius change. The periodic subatmospheric pressure change was further applied until the MR signal change was only due to the bubble radius change. An excellent MR sensitivity of 28 % bar-1 is demonstrated, bubble radii of 2.4 and 1.8 μm are numerically estimated before and after the application of pressure, and the simulations are further used to estimate the optimum bubble radius maximising the MR sensitivity to a small change in radius.

Although flowing foams are used in a variety of technologies, foam rheology is still incompletely understood. In this paper we demonstrate the use of a velocity-sensitised magnetic resonance imaging (MRI) sequence for the study of flowing foam. We employ a constant-time (pure phase encode) imaging technique, SPRITE, which is immune to geometrical distortions caused by the foam-induced magnetic field inhomogeneity. The sample magnetisation is prepared before the SPRITE imaging with the Cotts 13-interval motion-sensitisation sequence, which is also insensitive to the effects of the foam heterogeneity. We measure the development of a power-law velocity profile in the foam downstream of a Venturi constriction (in which the cross-section of the tube decreases by 89% in area) in a vertical, cylindrical pipe.

We propose a method that allows probing quantitatively the individual saturations of crudeoil/brine/mud-filtrate mixtures during imbibition-drainage experiments on a petroleum rock-system. The experiments have been also performed at different temperature and pressure conditions.

We used NMR techniques to probe the anisotropic properties of stretched Nafion®115membranes. The alignment of the polymeric structure under a uniaxial load is at the origin of a strong anisotropy of both the water self-diffusion coefficient and the proton conductivity. The determination of these two important membrane properties may lead to new fundamental information on the nature of the proton transport mechanisms in such oriented weaklycharged systems.

Relaxation Exchange Spectroscopy (REXSY) has not previously been performed on samples containing different liquids. We present a pulse sequence that combines a Pulsed Gradient Spin Echo with REXSY, which we call PGSE-REXSY. Using this pulse sequence it is possible to separate the signals from two liquid components, here oil and water, simultaneously present within a sample due to the difference in diffusion properties. A REXSY analysis can then be performed on the individual liquids. The technique is very relevant to applications in petroleum research, and could potentially be used to determine how the mobility of one liquid is influenced by the presence of the other. We also show that compared to a two-dimensional Inverse Laplace Transform, a discrete multi-exponential component model is more robust when performing a quantitative analysis of REXSY data.