Surface diffusion and flow activation energies of perfluoropolyalkylether

1995 ◽  
Vol 1 (2-3) ◽  
Author(s):  
TeresaM. O'Connor ◽  
MyungS. Jhon ◽  
CharlesL. Bauer ◽  
ByungG. Min ◽  
DoY. Yoon ◽  
...  
Keyword(s):  
Surface Diffusion ◽  
Activation Energies ◽  
Flow Activation

Anomalous Flow of Polyisobutylene

1967 ◽  
Vol 40 (5) ◽  
pp. 1492-1504
Author(s):  
J. Kenneth Lund
Keyword(s):  
Polymer Melt ◽  
Activation Energies ◽  
The Other ◽  
Rotating Flow ◽  
Viscosity Data ◽  
Flow Units ◽  
Uniform Shear ◽  
Shear Degradation ◽  
New Type ◽  
Flow Activation

Abstract This work began as a study of shear degradation in a polymer melt subjected to a uniform shear field. A new type of biconical rotor rheometer was designed and constructed for it. Early in the investigation, however, phenomena were observed which led our efforts away from the original objectives. Viscosity data on a polyisobutylene melt have been obtained which indicate the presence of two flow regions, having significantly different flow activation energies. Normal entanglement flow is encountered in one, the other is apparently dominated by a different mechanism, which results in lower flow activation energies. A mechanism involving rotating flow units is proposed and applied to describe this region.

Growth Properties of the Si(100) Steps: A Molecular Dynamics Study

1991 ◽  
Vol 237 ◽  
Author(s):  
Christopher Roland ◽  
George H. Gilmer
Keyword(s):  
Molecular Dynamics ◽  
Surface Diffusion ◽  
Binding Sites ◽  
Activation Energies ◽  
Step Edge ◽  
Lower Activation ◽  
Growth Properties ◽  
Molecular Dynamics Methods ◽  
Energy Surfaces

ABSTRACTWe have mapped out the energy surfaces seen by a single silicon adatom over the Si(100) surface and Si(100) steps, using Molecular Dynamics methods. This identifies the most likely binding sites as well as the activation energies for diffusion over the terraces and steps. We find that only the 5e step with no rebonded atoms is a good sink for adatoms - the SA, rebonded Sb and Db steps are weak sinks. Because of a higher density of binding sites and lower activation energies for surface diffusion along die step edge, we expect mat growth at the Sb and Db steps take place much more readily man at the SA step.

Diffusion and flow of gases and vapours through micropores II. Surface flow

1950 ◽  
Vol 203 (1073) ◽  
pp. 165-178 ◽  
Keyword(s):  
Surface Diffusion ◽  
Gaseous Phase ◽  
Diffusion Coefficients ◽  
Activation Energies ◽  
Surface Flow ◽  
Adsorbent Surface ◽  
Flow Through

Flow through porous plugs has been measured under conditions where surface flow of adsorbed gases makes an important contribution. An analysis of variables affecting surface flow enables surface diffusion coefficients to be calculated and has indicated conditions likely to reduce the correction for flow in the gaseous phase to small proportions. This has been confirmed by studying the effect of variations of porosity. Surface diffusion coefficients tend to increase with ‘coverage' of the adsorbent surface. This requires further study. Activation energies measured for one system were found to be rather small. Owing to the variation of surface diffusion coefficients with coverage, it proved difficult to obtain accurate values. Activation energies indicated a tendency to decrease as coverage increases. Further experiments on these points are also being carried out.

Effects of viscous flow activation energies and viscosities on waterborne light-diffusion dip-coatings

2019 ◽  
Vol 48 (5) ◽  
pp. 415-420
Author(s):  
Tian Fang ◽  
Daiyong Ye
Keyword(s):  
Shear Rate ◽  
Viscous Flow ◽  
Activation Energies ◽  
Rotational Viscometer ◽  
Acrylic Emulsion ◽  
Environment Friendly ◽  
Content Type ◽  
Shear Rates ◽  
Flow Activation ◽  
Light Diffusion

Purpose This paper aims to prepare good waterborne light-diffusion dip-coatings (WLDDC) for the glass lampshade inner walls of LED lamp tubes, the effects of viscosities and viscous flow activation energies on these dip-coatings were investigated. Design/methodology/approach The WLDDC were prepared using white pigments, light-diffusion agents, additives and an acrylic emulsion. The dip-coatings were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and a digital rotational viscometer, respectively. The effects of shear rates, temperatures and solids contents on the viscosities of the dip-coatings were studied. The viscous flow activation energies of these dip-coatings and the emulsion were calculated, compared and studied, respectively. Findings The results showed that the non-Newtonian behaviors of these dip-coatings were more prominent than that of the acrylic emulsion. When the temperature was maintained to be a constant and the shear rate was increased, the viscosity decreased and the shear stress increased. When the shear rate was maintained to be a constant, the viscosity decreased with increasing temperatures. The viscous flow activation energies of these dip-coatings decreased with the increasing shear rates. The higher solid contents of WLDDC were, the more its viscosity would decrease with the increasing shear rates, the more prominent its non-Newtonian behaviors would show. Practical implications A sample of good WLDDC with balanced properties was illustrated. Originality/value This investigation benefits to investigate waterborne environment-friendly dip-coatings for the inner glass walls of lamp tubes. This research provides an approach to optimize the viscosity parameters of light-diffusion dip-coatings.

Initial Stage of Titanium Slicide Formation on Si(Lll) Substrate

1995 ◽  
Vol 402 ◽  
Author(s):  
S. Shingubara ◽  
S. Takata ◽  
E. Takahashi ◽  
S. Konagata ◽  
H. Sakaue ◽  
...  
Keyword(s):  
Activation Energy ◽  
Detailed Analysis ◽  
Surface Diffusion ◽  
Temperature Regime ◽  
Activation Energies ◽  
Growth Mode ◽  
Diffusion Activation Energy ◽  
Dangling Bonds ◽  
Initial Stage ◽  
Diffusion Activation

AbstractDetailed analysis of Ti and/or TiSi2 islands growth have been made by UHV-STM observations after Ti deposition and subsequent annealing. It is shown that islands growth mode changes drastically at about 500 U for both cases on Si(111)-7×7 and on H-terminated Si(lll)-l×l. In the temperature regime higher than 500 °C, activation energies of islands growth are 1.12eV and 0.56eV for Si(M11)-7×7 and H-terminated Si(111) respectively. It is speculated that residual H-atoms combined with Si dangling bonds lowered surface diffusion activation energy.

Evidence of Surface Diffusion of Water Molecules on Proteins of Rabbit Lens by NMR Relaxation Measurements

1996 ◽  
Vol 51 (1-2) ◽  
pp. 81-90 ◽  
Author(s):  
Jerzy Bodurka ◽  
Gerd Buntkowsky ◽  
Aleksander Gutsze
Keyword(s):  
Surface Diffusion ◽  
Spin Relaxation ◽  
Rotational Diffusion ◽  
Activation Energies ◽  
Translational Diffusion ◽  
Spin Lattice Relaxation ◽  
Dynamic Processes ◽  
Water Molecules ◽  
Relaxation Measurements ◽  
Translational Surface

Abstract In this work, we propose a relaxation model for the interpretation of NMR proton spinlattice and spin-spin relaxation times of mammalian lenses. The framework for this model is based on nuclear magnetic spin-lattice relaxation measurements as a function of tem perature at different Larmor frequencies for whole rabbit lenses and fragments of the lens. According to this model, two different dynamic processes of the water molecules determine the relaxation behaviour, namely rotational diffusion and translational surface diffusion. These dynamic processes in conjuction with a two site exchange model give a good explanation of all the measured relaxation data. From the experimental data, we were able to obtain the activation parameters for rotational and translational diffusion of bound lens water. Correlation times of 2.1×10-11 sec and 2.5×10-9 sec and activation energies of 20.5 kJ/mol and 22.5 kJ/mol respectively were found at 308K. At low Larmor frequencies (≤ MHz) the longitudinal relaxation is mainly determined by translational surface diffusion of bound water with a mean square displacement of 1.5 nm, whereas at higher frequencies (≥300 MHz), rotational diffusion is the main relaxation mechanism. The spin-spin relaxation is determined by translational diffusion over the whole frequency range and therefore shows only a very small dispersion. By our model it is possible to explain: 1) the strikingly large difference between the T1 value and the T2A and T2B values observed in the lens and 2 ) the different values of the activation energies measured at different fields for the lens.

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.

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