Solution and Diffusion in Silicone Rubber. I. A Comparison with Natural Rubber

1963 ◽  
Vol 36 (3) ◽  
pp. 642-650 ◽  
Author(s):  
R. M. Barrer ◽  
J. A. Barrie ◽  
N. K. Raman
Keyword(s):  
Statistical Theory ◽  
Natural Rubber ◽  
Silicone Rubber ◽  
Diffusion Coefficients ◽  
Molecular Size ◽  
Low Energy ◽  
Kcal Mole ◽  
Self Diffusion ◽  
Order Of Magnitude ◽  
And Diffusion

Abstract The diffusion and solubility of n- and isobutane and of n- and neopentane has been studied in the range 30° to 70° C, in polydimethylsiloxane rubbers. The solubilities are very similar to those in natural rubbers and show comparable agreement with the statistical theory of polymer penetrant mixtures. Diffusion coefficients are at least an order of magnitude greater in silicone than in natural rubbers. The very low energy of activation, ED, of about 4 kcal/mole is almost invariant among the hydrocarbons studied and is the same as for self-diffusion and viscous flow in this rubber. The low value of ED means that permeabilities of the hydrocarbons increase as the temperature falls. Because diffusion in silicones is less dependent upon molecular size and shape of penetrant than in natural rubber, the silicones are less selective though much more permeable separation barriers.

scholarly journals Quantifying Diffusion in a Biofilm ofStreptococcus mutans

2010 ◽  
Vol 55 (3) ◽  
pp. 1075-1081 ◽  
Author(s):  
Zeshi Zhang ◽  
Elena Nadezhina ◽  
Kevin J. Wilkinson
Keyword(s):  
Ionic Strength ◽  
Fluorescent Probes ◽  
Diffusion Coefficients ◽  
Correlation Spectroscopy ◽  
Fluorescence Correlation ◽  
Self Diffusion ◽  
Probe Size ◽  
Order Of Magnitude ◽  
Biofilm Heterogeneity ◽  
Insight Into

ABSTRACTIn biofilms, diffusion may limit the chemical activity of nutrients, toxic compounds, and medicines. This study provides direct, noninvasive insight into the factors that will most effectively limit the transport of antibiotics and biocides in biofilms. Self-diffusion coefficients have been determined for a number of fluorescent probes in biofilms ofStreptococcus mutansusing fluorescence correlation spectroscopy. The effects of probe size and charge and the roles of biofilm pH, ionic strength, and heterogeneity were studied systematically. The relative diffusion coefficients (Din the biofilm divided by that in water) decreased with increasing probe size (3,000-molecular-weight [3K], 10K, 40K, 70K, and 2,000K dextrans). Studies using variably charged substrates (tetramethylrhodamine, Oregon Green, rhodamine B, and rhodamine 6G) showed that the self-diffusion coefficients decreased with an increasing negative charge of the fluorescent probes. No significant effect was observed for changes to the ionic strength (10−4to 10−1M) or pH (4 to 9) of the biofilm. Biofilm heterogeneity was responsible for variations of ca. one order of magnitude in the diffusion coefficients.

Point Defects and Diffusion in Ni3Ga

1998 ◽  
Vol 527 ◽  
Author(s):  
T. IKEDA ◽  
A. Almazouzi ◽  
A. Funao ◽  
H. Numakura ◽  
M. Koiwa ◽  
...  
Keyword(s):  
Point Defects ◽  
Positron Lifetime ◽  
Major Element ◽  
Tracer Diffusion ◽  
The Self ◽  
Self Diffusion ◽  
Order Of Magnitude ◽  
Constituent Elements ◽  
Tracer Diffusion Coefficients ◽  
And Diffusion

ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constituent elements in Ni3Ga have been studied by positron annihilation, tracer diffusion and interdiffusion experiments. Thermal vacancies have been detected by positron lifetime measurements for specimens quenched from high temperatures. The vacancy formation energy is in the range between 1.7 and 1.8 eV, and is not dependent strongly on the composition. The tracer diffusion coefficients of Ni and Ga are of the same order of magnitude, and the interdiffusion coefficient is about 10 times larger than the diffusion coefficient of Ni. The diffusion in Ni3Ga has been found to satisfy the Darken-Manning equation, as expected from the model of the self-diffusion in this type of materials, where both the species of atoms are assumed to migrate primarily in the sub-lattice of the major element via the ordinary vacancy mechanism.

Solution and diffusion in silicone rubber I—A comparison with natural rubber

Polymer ◽  
1962 ◽  
Vol 3 ◽  
pp. 595-603 ◽  
Author(s):  
R BARRER ◽  
J BARRIE ◽  
N RAMAN
Keyword(s):  
Natural Rubber ◽  
Silicone Rubber ◽  
And Diffusion

scholarly journals Molecular dynamic simulation study of molten cesium

2017 ◽  
Vol 82 (6) ◽  
pp. 681-694 ◽  
Author(s):  
Saeid Yeganegi ◽  
Vahid Moeini ◽  
Zohreh Doroodi
Keyword(s):  
Internal Pressure ◽  
Diffusion Coefficients ◽  
Distribution Functions ◽  
Radial Distribution Functions ◽  
Coordination Numbers ◽  
Self Diffusion ◽  
Temperature And Pressure ◽  
Molecular Dynamic Simulation Study ◽  
Dynamics Simulations ◽  
And Diffusion

Molecular dynamics simulations were performed to study thermodynamics and structural properties of expanded caesium fluid. Internal pressure, radial distribution functions (RDFs), coordination numbers and diffusion coefficients have been calculated at temperature range 700?1600 K and pressure range 100?800 bar. We used the internal pressure to predict the metal?non-metal transition occurrence region. RDFs were calculated at wide ranges of temperature and pressure. The coordination numbers decrease and positions of the first peak of RDFs slightly increase as the temperature increases and pressure decreases. The calculated self-diffusion coefficients at various temperatures and pressures show no distinct boundary between Cs metallic fluid and its expanded fluid where it continuously increases with temperature.

scholarly journals Aggregation Behavior of 6-Isocassine and N-Methyl-6-Isocassine: Insights into the Biological Mode of Action of Lipid Alkaloids

2016 ◽  
Vol 11 (11) ◽  
pp. 1934578X1601101
Author(s):  
Luis Reina ◽  
Gualberto Bottini ◽  
Zohra Bennadji ◽  
Vittorio Vinciguerra ◽  
Fernando Ferreira ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Diffusion Coefficients ◽  
Mode Of Action ◽  
Aggregation Behavior ◽  
The Self ◽  
Self Diffusion ◽  
And Diffusion

The aggregation behavior of 6-isocassine and N-methyl-6-isocassine, two piperidin-3-ol alkaloids isolated respectively from the barks of Prosopis nigra and P. affinis, was investigated using a combination of NOE experiments and diffusion measurements in solvents of varying polarity and hydrogen bonding capacity. While the NOE enhancements for N-methyl-6-isocassine are positive, regardless of the solvent, those for 6-isocassine shift from negative to positive when going from chloroform- d to methanol- d 4 solution. In addition, despite the self-diffusion coefficients of both compounds being virtually identical in methanol- d 4, N-methyl-6-isocassine diffuses nearly twice as fast as the non-methylated alkaloid in chloroform- d. The changes in rotational and translational dynamics observed between solvents for 6-isocassine suggest that the molecule forms dimeric head-to-head aggregates in non-polar aprotic environments, a behavior that could help explain the biological mode of action that has been proposed for this type of alkaloids.

Kinetic Model of Fluids Molecules Diffusion in Porous Media

2011 ◽  
Vol 6 (4) ◽  
pp. 89-94
Author(s):  
Vladimir Andryushchenko ◽  
Valeriy Rudyak
Keyword(s):  
Porous Media ◽  
Diffusion Coefficients ◽  
Fluid Density ◽  
Dynamics Modeling ◽  
Molecular Fluids ◽  
Self Diffusion ◽  
Molecular Dynamics Modeling ◽  
Diffusion In Porous Media ◽  
Modeling Data ◽  
And Diffusion

Model of molecular fluids diffusion in porous media develop on the base of elementary kinetic theory. The dependence of self-diffusion and diffusion coefficients from pore sizes, porosity, and fluid density has been obtained. The predictions of created model have been compared with molecular dynamics modeling data

Diffusion and flow of gases and vapours through micropores III. Surface diffusion coefficients and activation energies

1951 ◽  
Vol 209 (1096) ◽  
pp. 38-58 ◽  
Keyword(s):  
Surface Diffusion ◽  
Diffusion Coefficients ◽  
Capillary Condensation ◽  
Molecular Size ◽  
Limited Range ◽  
Activation Energies ◽  
High Activation ◽  
Adsorbent Surface ◽  
Adsorbed Layers ◽  
Order Of Magnitude

When less than a complete monolayer is present, surface-diffusion coefficients decrease rapidly with decreasing coverage. This is attributed to variation in heats of adsorption over the adsorbent surface. Diffusion is due to the most loosely bound molecules, and these tend to disappear first as coverage decreases. Only a limited range of coverage could be followed in a given system and, within this, activa­tion energies showed no marked variation. This should follow if molecules which require high activation energies play relatively little part in surface diffusion. In no system so far studied have activation energies been small enough to support the existence of ‘freely mobile’ or ‘gas-like’ adsorbed layers. A gas-like state is not approached at low coverages, since molecules adsorbed under these conditions are practically immobile. Surface diffusion coefficients compared at constant temperature and constant coverage differ for various molecules according to differences in molecular size, shape and polar character. When the monolayer is complete and multilayers are formed, diffusion coefficients are little dependent on coverage, and, though perhaps higher than for diffusion in the liquid state, are of a similar order of magnitude. Capillary condensation, in at least the initial stages, produces a rapid rise in surface-diffusion coefficients. Measurements in this region have only limited reproducibility. The importance of pore structure on the shape of adsorption isotherms is stressed. Its effect on surface-diffusion coefficients is indicated, but has not been followed in detail.

scholarly journals Non-Exponential 1H and 2H NMR Relaxation and Self-Diffusion in Asphaltene-Maltene Solutions

Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5218
Author(s):  
Kevin Lindt ◽  
Bulat Gizatullin ◽  
Carlos Mattea ◽  
Siegfried Stapf
Keyword(s):  
Diffusion Coefficients ◽  
Relaxation Times ◽  
Chemical Species ◽  
Nmr Relaxation ◽  
Molecular Size ◽  
Relaxation Rates ◽  
Vast Number ◽  
Self Diffusion ◽  
Slowing Down ◽  
The Individual

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions—either through steric hindrances or promoted by aromatic-aromatic interactions—are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes’ NMR relaxation (T1 and T2) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes’ dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes’ aromaticity on the maltene–asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.

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