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Membrane Decreases (membrane + decrease)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Synthesis of charged ultrafiltration poly(styrene- co -divinyl benzene) composite membrane

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
Sonny Sachdeva
Abstract A ceramic supported crosslinked polystyrene composite membrane has been prepared from its monomers using a dual initiator system. The nonionic hydrophobic membrane so prepared has been chemically modified by a low temperature (50°C), single step reaction with chloroacetic acid. The carboxylated membrane has acid functional groups on its surface making it negatively charged and highly hydrophilic in nature. The membranes (unmodified and carboxylated) have been used for the separation of hazardous chromium (VI) salt solution where observed and intrinsic rejection has been studied as a function of pressure and concentration of the feed solution. The intrinsic rejection has been determined by calculating the concentration at the membrane surface (Cm) using Speigler-Kedam model and osmotic pressure model. The observed rejection for the chemically modified membrane decreases with increasing pressure but the intrinsic rejection is found to be more than 80% for all concentrations in the range of study. The experimental results have been fitted using Space-Charge model to obtain the membrane wall potential and the membrane surface concentration which are difficult to measure directly. The transport through the membrane capillaries has been described by the two dimensional model using Nernst-Planck equation for ion transport, Navier-Stokes equation and Poisson-Boltzmann equation for the radial distribution of potential. We have then presented a semianalytical series solution to the highly nonlinear Poisson-Boltzmann equation to reduce the computational time required to solve the set of coupled differential equations. The effective wall potential of the carboxylated membrane was found to be ,28.07 mV. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effect Of Plasma Cholesterol On Red Blood Cell Oxygen Transport

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 12 2000
Henry Buchwald
SUMMARY 1. Oxygen (O2) transfer from the blood to tissues is a function of the red blood cell (RBC) O2 saturation (SO2), the plasma O2 content being negligible. Under conditions of increased tissue O2 demand, the SO2 of arterial blood does not change appreciably (97%); however, the SO2 of mixed venous blood, equal to that of the perfused tissues, can go as low as 20%. 2. Tissue O2 availability is limited by the exposure time to a RBC, which decreases under conditions of maximum stress (< 1 s). If the O2 unloading time was to increase significantly, because of a decrease in the RBC diffusion constant or an increase in the RBC membrane thickness, the RBC O2 unloading time would exceed tissue (e.g. cardiac) transit time and O2 transfer would be impaired. 3. Cholesterol constitutes the non-polar, hydrophobic lipid of the enveloping layer of the RBC membrane. As the cholesterol content of the RBC increases, the fluidity of the membrane decreases and the lipid shell stiffens. 4. Early studies demonstrated that high blood cholesterol concentrations were associated with reduced blood O2 transport; in essence, the haemoglobin dissociation curve was shifted to the left. 5. Current investigations have shown that the cholesterol RBC membrane barrier to O2 diffusion delayed O2 entry into the RBC during saturation and delayed O2 release from the RBC during desaturation. In an analysis of 93 patients divided by their cholesterol concentration into five groups, the percentage change in blood O2 diffusion was inversely proportional to the cholesterol concentration. 6. The RBC membrane cholesterol is in equilibrium with the plasma cholesterol concentration. It stands to reason that as the plasma cholesterol increases, the RBC membrane becomes impaired and O2 transport is reduced. 7. The implications of this new perspective on O2 transport include the ability to increase tissue oxygenation by lowering plasma cholesterol. [source]

Metal Ion Implantation for the Fabrication of Stretchable Electrodes on Elastomers

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Samuel Rosset
Abstract Here, the use of low-energy metal ion implantation by filtered cathodic vacuum arc to create highly deformable electrodes on polydimethylsiloxane (PDMS) membranes is reported. Implantation leads to the creation of nanometer-size clusters in the first 50,nm below the surface. When the elastomer is stretched, these small clusters can move relative to one another, maintaining electrical conduction at strains of up to 175%. Sheet resistance versus ion dose, resistance versus strain, time stability of the resistance, and the impact of implantation on the elastomer's Young's modulus are investigated for gold, palladium, and titanium implantations. Of the three tested metals, gold has the best performance, combining low and stable surface resistance, very high strain capabilities before loss of electrical conduction, and low impact on the Young's modulus of the PDMS membrane. These electrodes are cyclically strained to 30% for more than 105 cycles and remain conductive. In contrast, sputtered or evaporate metals films cease to conduct at strains of order 3%. Additionally, metal ion implantation allows for creating semi-transparent electrodes. The optical transmission through 25-µm-thick PDMS membranes decreases from 90% to 60% for Pd implantations at doses used to make stretchable electrodes. The implantation technique presented here allows the rapid production of reliable stretchable electrodes for a number of applications, including dielectric elastomer actuators and foldable or rollable electronics. [source]

Effect of metal-support interface on hydrogen permeation through palladium membranes

AICHE JOURNAL, Issue 3 2009
Ke Zhang
Abstract Thin palladium membranes of different thicknesses were prepared on sol-gel derived mesoporous ,-alumina/,-alumina and yttria-stabilized zirconia/,-alumina supports by a method combining sputter deposition and electroless plating. The effect of metal-support interface on hydrogen transport permeation properties was investigated by comparing hydrogen permeation data for these membranes measured under different conditions. Hydrogen permeation fluxes for the Pd/,-Al2O3/,-Al2O3 membranes are significantly smaller than those for the Pd/YSZ/,-Al2O3 membranes under similar conditions. As the palladium membrane thickness increases, the difference in permeation fluxes between these two groups of membranes decreases and the pressure exponent for permeation flux approaches 0.5 from 1. Analysis of the permeation data with a permeation model shows that both groups of membranes have similar hydrogen permeability for bulk diffusion, but the Pd/,-Al2O3/,-Al2O3 membranes exhibit a much lower surface reaction rate constant with higher activation energy, due possibly to the formation of Pd-Al alloy, than the Pd/YSZ/,-Al2O3 membranes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]