Filler-Elastomer Interactions. Part V. Investigation of the Surface Energies of Silane-Modified Silicas

1992 ◽  
Vol 65 (4) ◽  
pp. 715-735 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff
Keyword(s):  
Surface Energy ◽  
Energy Distribution ◽  
Strong Dependence ◽  
Free Energies ◽  
Specific Component ◽  
Dispersive Component ◽  
Initial Silica ◽  
Finite Concentration ◽  
Modified Surface ◽  
High Degree

Abstract As shown in previous papers of this series, the main feature of silicas with regard to surface energy, which distinguishes them from carbon blacks, is a low dispersive component, γsd, and a high specific component, γssp, of surface energy. The low γsd, would result in a lack of interaction between filler and hydrocarbon rubbers, while the high γssp would suggest a high degree of agglomeration of the filler particles in the polymer matrix. In this study, the surface free energies and the energy distribution on the surfaces of precipitated silicas which had been modified with octadecyltrimethoxy silane, 3-thiocyanatopropyltriethoxy silane and bis(3-trimethoxysilylpropyl)-tetrasulfane, respectively, were investigated by chromatography at infinite dilution and at finite concentration. A comparison with the initial silica suggests a drastic decrease in surface energy, especially of the specific component, as a result of the modification and a strong dependence of surface energy on the chemical nature of the grafts and the ratio of these grafts. The energy distribution function shows that, while the surface of the ungrafted silica is heterogeneous, the heterogeneity of the fully modified surface is drastically reduced, particularly when the product was modified with octadecyltrimethoxy silane.

Filler—Elastomer Interactions. Part III. Carbon-Black-Surface Energies and Interactions with Elastomer Analogs

1991 ◽  
Vol 64 (5) ◽  
pp. 714-736 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff ◽  
Jean-Baptiste Donnet
Keyword(s):  
Surface Energy ◽  
Carbon Black ◽  
Surface Area ◽  
Particle Interaction ◽  
Crystallographic Structure ◽  
Specific Component ◽  
Dispersive Component ◽  
Carbon Blacks ◽  
Surface Energies ◽  
Very High

Abstract The surface energies, both the dispersive component, γsd, and the specific component, γssp, of dry- and wet-pelletized carbon blacks, ranging from N110 to N990, were evaluated by inverse gas-solid chromatography at infinite dilution. The results indicate that the dispersive components of the surface energy of carbon blacks increase with increasing surface area. This dependence may essentially reflect an effect of microstructure on the surface energies, which can be confirmed by the relationship between the crystallographic parameters of crystallites and the graphitization of the carbon blacks. It was found that smaller crystallites characterized by a lower value of Lc lead to higher surface energy, whereas graphitization of the carbon black points toward lower surface energy, perhaps resulting from the growth of the quasi-graphite structure. Surface area dependence of the specific component of the surface energy characterized by the specific energy of adsorption of a polar probe follows the same pattern as was observed for the dispersive component, i.e., γsd increases with surface area. This is believed to be related to the crystallographic structure and the surface chemistry. Studies on adsorption energies of the low-molecular-weight analogs of elastomers generally show that the interactions between carbon blacks and rubbers depend not only on filler surface energies but also on the structure of the elastomers. Due to their polar functional groups, NBR and SBR show a stronger interaction with blacks than unsaturated rubbers. Among the rubbers simulated, IIR would have the lowest interaction with the filler. A comparison of the surface energies of carbon blacks and silicas points toward a very high γsd, for blacks which may show strong interaction with nonpolar- or low-polar polymers, while the very high Sf value of the silicas, especially precipitated silicas, a measure of the relative polarity of their surface, is considered to be representative of strong particle-particle interaction, leading to the formation of a filler network.

Understanding Conformational Entropy in Small Molecules

2020 ◽  
Author(s):  
Lucian Chan ◽  
Garrett Morris ◽  
Geoffrey Hutchison
Keyword(s):  
Small Molecules ◽  
Degrees Of Freedom ◽  
Absolute Error ◽  
Low Energy ◽  
Standard Entropy ◽  
Free Energies ◽  
Conformational Entropy ◽  
Wide Range ◽  
High Degree ◽  
Empirical Corrections

The calculation of the entropy of flexible molecules can be challenging, since the number of possible conformers grows exponentially with molecule size and many low-energy conformers may be thermally accessible. Different methods have been proposed to approximate the contribution of conformational entropy to the molecular standard entropy, including performing thermochemistry calculations with all possible stable conformations, and developing empirical corrections from experimental data. We have performed conformer sampling on over 120,000 small molecules generating some 12 million conformers, to develop models to predict conformational entropy across a wide range of molecules. Using insight into the nature of conformational disorder, our cross-validated physically-motivated statistical model can outperform common machine learning and deep learning methods, with a mean absolute error ≈4.8 J/mol•K, or under 0.4 kcal/mol at 300 K. Beyond predicting molecular entropies and free energies, the model implies a high degree of correlation between torsions in most molecules, often as- sumed to be independent. While individual dihedral rotations may have low energetic barriers, the shape and chemical functionality of most molecules necessarily correlate their torsional degrees of freedom, and hence restrict the number of low-energy conformations immensely. Our simple models capture these correlations, and advance our understanding of small molecule conformational entropy.

Understanding Conformational Entropy in Small Molecules

2021 ◽  
Author(s):  
Lucian Chan ◽  
Garrett Morris ◽  
Geoffrey Hutchison
Keyword(s):  
Small Molecules ◽  
Degrees Of Freedom ◽  
Absolute Error ◽  
Low Energy ◽  
Standard Entropy ◽  
Free Energies ◽  
Conformational Entropy ◽  
Wide Range ◽  
High Degree ◽  
Empirical Corrections

The calculation of the entropy of flexible molecules can be challenging, since the number of possible conformers grows exponentially with molecule size and many low-energy conformers may be thermally accessible. Different methods have been proposed to approximate the contribution of conformational entropy to the molecular standard entropy, including performing thermochemistry calculations with all possible stable conformations, and developing empirical corrections from experimental data. We have performed conformer sampling on over 120,000 small molecules generating some 12 million conformers, to develop models to predict conformational entropy across a wide range of molecules. Using insight into the nature of conformational disorder, our cross-validated physically-motivated statistical model can outperform common machine learning and deep learning methods, with a mean absolute error ≈4.8 J/mol•K, or under 0.4 kcal/mol at 300 K. Beyond predicting molecular entropies and free energies, the model implies a high degree of correlation between torsions in most molecules, often as- sumed to be independent. While individual dihedral rotations may have low energetic barriers, the shape and chemical functionality of most molecules necessarily correlate their torsional degrees of freedom, and hence restrict the number of low-energy conformations immensely. Our simple models capture these correlations, and advance our understanding of small molecule conformational entropy.

Stress Distribution in and Around Spheroidal Inclusions and Voids at Finite Concentration

1986 ◽  
Vol 53 (3) ◽  
pp. 511-518 ◽  
Author(s):  
G. P. Tandon ◽  
G. J. Weng
Keyword(s):  
Stress Distribution ◽  
Energy Distribution ◽  
Uniaxial Tension ◽  
Elastic Stress ◽  
Three Dimensional ◽  
Tensile Loading ◽  
Form Solution ◽  
Finite Concentration ◽  
The Matrix ◽  
Close Form

A simple, albeit approximate, close-form solution is developed to study the elastic stress and energy distribution in and around spheroidal inclusions and voids at finite concentration. This theory combines Eshelby’s solution of an ellipsoidal inclusion and Mori- Tanaka’s concept of average stress in the matrix. The inclusions are taken to be homogeneously dispersed and undirectionally aligned. The analytical results are obtained for the general three-dimensional loading, and further simplified for uniaxial tension applied parallel to the axis of inclusions. The ensuing stress and energy fields under tensile loading are illustrated for both hard inclusions and voids, ranging from prolate to oblate shapes, at several concentrations.

scholarly journals Surface Energy Partitioning and Evaporative Fraction in a Water-Saving Irrigated Rice Field

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 51 ◽  
Author(s):  
Xiaoyin Liu ◽  
Junzeng Xu ◽  
Shihong Yang ◽  
Yuping Lv
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Energy Distribution ◽  
Water Saving ◽  
Rice Paddies ◽  
Irrigated Rice ◽  
Evaporative Fraction ◽  
Moisture Condition ◽  
Soil Moisture Condition ◽  
Available Energy

Surface energy distribution in paddy fields and the ratio of latent heat flux (LE) to available energy, termed as the evaporative fraction (EF), are essential for an understanding of water and energy processes. They are expected to vary in different ways in response to changes in the soil moisture condition under water-saving irrigation practice. In this study, the diurnal and seasonal variations in energy distribution were examined based on the data measured by the eddy covariance system and corrected with enforcing energy balance closure by the EF method in water-saving irrigated rice paddies in 2015 and 2016. Soil heat flux (G) values were similar in magnitude to sensible heat flux (Hs) values, with both accounting for approximately 5% of the energy input. Both magnitudes of G and Hs were significantly lower than that of LE. Generally, EF in water-saving irrigated rice paddies was larger than that of other ecosystems, and varied within a narrow range from 0.7 to 1.0. Diurnally, EF decreased till noon and then increased slowly in the afternoon till sunset. It was found be less varied between 10:00 and 14:00. Seasonally, the alternative drying-wetting soil water conditions in water-saving irrigated rice paddies resulted in a change in the variation of the EF. The LE flux is the largest component of available energy, with EF being mostly higher than 0.9. EF, increasing consistently till the tillering stage, remaining high from the late tillering to milk stage, and then following a declining trend. The maximum EF (approaching 1.0) was found in the milk stage. The results of EF in water-saving irrigated rice paddies will be helpful for estimating daily or long temporal scale evapotranspiration (ET) by the EF method based on satellite-derived ET.

scholarly journals Casimir effect modified surface energy of a nanocavity in homogeneous media

2015 ◽  
Vol 527 (7-8) ◽  
pp. 499-506
Author(s):  
Yi Zheng ◽  
Arvind Narayanaswamy
Keyword(s):  
Surface Energy ◽  
Casimir Effect ◽  
Modified Surface ◽  
Homogeneous Media

Filler-Elastomer Interactions. Part VI. Characterization of Carbon Blacks by Inverse Gas Chromatography at Finite Concentration

1992 ◽  
Vol 65 (5) ◽  
pp. 890-907 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff
Keyword(s):  
Gas Chromatography ◽  
Energy Distribution ◽  
Inverse Gas Chromatography ◽  
General Trend ◽  
High Energy ◽  
Carbon Blacks ◽  
Finite Concentration ◽  
Good Agreement

Abstract Carbon blacks ranging from N110 to N990 were characterized by means of inverse gas chromatography at finite concentration. The isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area. This is in good agreement with surface-energy measurements reported previously. The energy-distribution function of adsorption shows that while the concentrations of low-energy sites are comparable for most of the carbon blacks, differences exist with regard to high-energy sites. These suggest that small-particle-size blacks possess a greater number of high-energy centers. The graphitization of carbon blacks results in a considerable reduction in their adsorption capacity and narrows the energy distribution of their surfaces. One can therefore conclude that high-energy sites play an important role in the determination of the surface energies and reinforcing ability of carbon blacks.

Filler—Elastomer Interactions. Part IV. The Effect of the Surface Energies of Fillers on Elastomer Reinforcement

1992 ◽  
Vol 65 (2) ◽  
pp. 329-342 ◽  
Author(s):  
Siegfried Wolff ◽  
Meng-Jiao Wang
Keyword(s):  
Carbon Black ◽  
Small Strain ◽  
Rubber Content ◽  
Specific Component ◽  
Dispersive Component ◽  
Surface Energies ◽  
Precipitated Silica ◽  
Bound Rubber ◽  
High Elongation ◽  
Polymer Interaction

Abstract Carbon black N110 and a precipitated silica, which have comparable surface area and structure, were selected as model fillers to study the effect of filler surface energies on rubber reinforcement. In comparison with carbon black, the surface energies of silica are characterized by a lower dispersive component, γsd, and higher specific component, γssp. It was found that the high γssp of silica leads to strong interaggregate interaction, resulting in higher viscosity of the compounds, higher αƒ, and higher moduli of the vulcanizates at small strain. The higher γsd of carbon black, in contrast, causes strong filler—polymer interaction, which is reflected in a higher bound-rubber content of the compounds and higher moduli of the vulcanizates at high elongation.

The Nature and Action of Tackifier Resins

1988 ◽  
Vol 61 (3) ◽  
pp. 448-469 ◽  
Author(s):  
Derek W. Aubrey
Keyword(s):  
Phase Separation ◽  
Surface Energy ◽  
Response Times ◽  
Viscoelastic Behavior ◽  
High Energy ◽  
Phase Morphology ◽  
Two Phase ◽  
Chemical Structures ◽  
Separation Force ◽  
High Degree

Abstract A good tackifler resin appears to require a combination of high T9 at low molecular weight, and for this a highly condensed alicyclic structure appears to be desirable. Except for the rosin derivatives, the chemical structures of common tackifier resins are not fully resolved and some more definitive studies are needed. In addition, a high degree of miscibility of resin with rubber is important. Although some common tackifier resins cause phase separation over certain concentration ranges when blended with rubbers, this is probably exceptional, and it seems likely that most adhesive compositions are single phase in this respect. Where phase separation does occur, there is a need for fuller elucidation of the phase morphology and composition of the phases. The widely-held view that a two-phase morphology is necessary for the development of high tack appears to be incorrect. The few studies which have been carried out so far indicate that the surface energy of a rubber is modified only slightly by the incorporation of a tackifier resin. It is unlikely that this surface energy change can seriously affect the tack value as measured by the common form of probe test. The viscoelastic behavior of rubber-resin blends provides an adequate explanation for the phenomenon of tack. Over long response times, the low modulus (high compliance) of the blend compared with that of the rubber alone allows a high degree of intermolecular contact to be achieved during the bonding stage of a tack test. Over short response times, corresponding to the de-bonding stage of the test, the blend shows transition zone response with high energy dissipation and consequent high separation force. For further progress in our understanding, however, there is a need to distinguish clearly between the bonding and debonding effects of the resin and also for a more definitive study of the factors controlling the bonding stage.

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