Characterization and Monitoring of Porous Media with Electrical Imaging: A Review

Transport in Porous Media - Electrical geophysical imaging is a widely used noninvasive technology for visualizing porous media at scales larger than individual pores. Originally developed for...     

Effect of oxygen content on the 29Si NMR, Raman spectra and oxide ion conductivity of the apatite series, La8+xSr2-x(SiO4)6O2+x/2

29Si NMR data have been recorded for the apatite series La8+xSr2-x(SiO4)6O2+x/2 (0 < or = x < or = 1.0). For x = 0, a single NMR peak is observed at a chemical shift of approximately -77 ppm, while as the La : Sr ratio and hence interstitial oxygen content is increased, a second peak at a chemical shift of approximately -80 ppm is observed, which has been attributed to silicate groups neighbouring interstitial oxide ions. An increase in the intensity of this second peak is observed with increasing x, consistent with an increase in interstitial oxide ion content, and the data are used to estimate the level of interstitial oxide ions, and hence Frenkel-type disorder in these materials. The increase in second 29Si NMR peak intensity/interstitial oxide ion content is also shown to correlate with an increase in conductivity. The effect of interstitial oxygen content can also be studied by means of Raman spectroscopy, with a new mode at 360 cm(-1) appearing for samples with x > 0 in the symmetric bending mode energy region of the SiO4 group. The intensity of this mode increases with increasing oxygen content, yielding results comparable to those from the NMR studies, showing the complementarities of the two techniques.     

Experimental Confirmation of a Predicted Porous Hydrogen-Bonded Organic Framework

Hydrogen-bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure-property predictions to generate energy-structure-function (ESF) maps for a series of triptycene-based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low-energy HOF (TH5-A) with a remarkably low density of 0.374 g cm⁻³ and three-dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5-A polymorph experimentally. This material has a high accessible surface area of 3,284 m² g⁻¹, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date.     

Sequence effects on the forced translocation of heteropolymers through a small channel

By using a recently developed Monte Carlo algorithm and an exact numerical method, we calculate the translocation probability and the average translocation time for charged heterogeneous polymers driven through a nanopore by an external electric field. The heteropolymer chains are composed of two types of monomers (A and B) which differ only in terms of their electric charge. We present an exhaustive study of chains composed of eight monomers by calculating the average translocation time associated with the 256 possible arrangements for various ratios of the monomer charges (lambda(A)lambda(B)) and electric field intensities E. We find that each sequence leads to a unique value of the translocation probability and time. We also show that the distribution of translocation times is strongly dependent on the two forces felt by the monomers ( approximately lambda(A)E and approximately lambda(B)E). Finally, we present results that highlight the effect of having repetitive patterns by studying the translocation times of various block copolymer structures for a very long chain composed of N=2(18) monomers (all with the same number of A and B monomers).     

Determination of phosphate using a highly sensitive paired emitter-detector diode photometric flow detector

The use of a novel inexpensive photometric device, a paired emitter-detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit.The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert law were obtained for phosphate in the range of 0.02-2 μM. The dynamic range, sensitivity and limits of detection are reported.     

Advantages of deuterium-labelled mixed triacylglycerol in studies of intraluminal fat digestion

The (13)C-mixed triacylglcerol (MTG, 1,3-distearyl, 2-[1-(13)C]octanoyl glycerol) breath test is a non-invasive measure of intraluminal fat digestion. Recovery of (13)C in breath CO(2) is incomplete (<50%) owing to sequestration of (13)C into organic molecules via the tricarboxylic acid (TCA) cycle. In addition lack of knowledge of CO(2) production rate (VCO(2)) during the test leads to errors in the calculated percentage dose recovered (PDR). (2)H sequestration into organic molecules is low ( approximately 4%) and is not influenced by factors that affect VCO(2) such as food intake or physical activity. After oxidation of (2)H-labelled macromolecules, the label appears in body water, which can be sampled non-invasively in urine or saliva. After an overnight fast, two healthy adults consumed [(2)H]MTG (1,3-distearyl, 2-[(2)H(15)]octanoyl glycerol) and [(13)C]MTG (1,3 distearyl, 2-[1-(13)C]octanoyl glycerol) simultaneously. Total body water (TBW) was measured by (18)O dilution and also estimated from height and weight. Urine and saliva were sampled at baseline and for 10 h after consumption of the test meal. The abundance of (2)HOH and H(2) (18)O in urine and saliva was measured by continuous-flow isotope-ratio mass spectrometry. Cumulative PDR of (2)H and (18)O was calculated from the plateau enrichment, which was reached by 6 h in both saliva and urine. Recovery of (2)H calculated using measured TBW was compared with that using an estimated value of TBW. Mean recovery of (2)H in saliva was 99.3% and in urine was 96.4%. Errors introduced by estimating TBW were <5%. [(2)H]MTG could provide a simpler, more robust, indirect test of intraluminal fat digestion compared with the (13)C-breath test. Further studies are required in pancreatic insufficient patients.