The Kinetics of Rubberlike Elasticity

1942 ◽  
Vol 15 (3) ◽  
pp. 438-445
Author(s):  
D. D. Eley
Keyword(s):  
Viscous Flow ◽  
Internal Rotation ◽  
Similar Data ◽  
Chain Molecules ◽  
Polymer Systems ◽  
Vulcanized Rubber ◽  
Activated State ◽  
Main Effect ◽  
High Degree ◽  
Kinetics Of

Abstract 1. The treatments of relaxation phenomena in polymer systems, due to Kuhn, and Alexandrov and Lazurkin, are outlined and discussed. 2. Eyring's rate equation is used to analyze the rates of orientation of long-chain molecules in a stressed specimen of lightly vulcanized rubber. The data are compared with similar data on viscous flow in raw rubber, and it is suggested that the segment size for movement is the same in both cases. In viscous flow, the segmental movement occurs without appreciable internal rotation within the segment. In elastic orientation, however, it appears that a high degree of internal rotation within the segment accompanies the formation of the activated state. 3. The activation energy for the orientation of long chains is separated into two terms: (1) the energy required to free a segment from its neighbors, (2) the energy of activation for rotation around C—C bonds. It is suggested that the main effect of vulcanization and plasticizers is on term (3); vulcanization tends to increase this term, plasticizers to decrease it. 4. Data on the dielectric dispersion of polyvinyl chloride suggests the need for internal rotational activation in this case, as in orientation elasticity. This is in agreement with what we should qualitatively expect. Possible complications due to crystallinity in rubber at high extensions or low temperatures are briefly discussed.

DNA—RNA hybridization

1975 ◽  
Vol 272 (915) ◽  
pp. 147-157 ◽  
Keyword(s):  
Nucleic Acid ◽  
Complex Mixture ◽  
Nucleic Acid Hybridization ◽  
Biological Research ◽  
Specific Sequence ◽  
Different Populations ◽  
Higher Eukaryotes ◽  
High Degree ◽  
Kinetics Of ◽  
Specific Sequences

Interest in nucleic acid hybridization stems mainly from its great power as a tool in biological research. It is used in several quite distinct ways. Because of the high degree of specificity that they show, hybridization techniques can be used to measure the amount of one specific sequence within a very heterogeneous mixture of sequences. Measurements of 1/10 6 -10 7 have been recorded. In extension of this, various properties of a specific sequence can often be studied. Secondly, because the kinetics of nucleic acid hybridization are quite well understood, it can be used to characterize both a pure sequence and a very complex mixture of sequences, like the genome of a vertebrate. Thirdly, again because of its specificity, it can be used to measure homologies between different populations of nucleic acids. Lastly, in conjunction with other techniques, it can be used as a basis for the fractionation of nucleic acid populations and the purification of specific sequences. Specific examples of these applications are given, with special reference to the organization of the genome in higher eukaryotes.

Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber

1951 ◽  
Vol 24 (4) ◽  
pp. 777-786
Author(s):  
E. H. Farmer ◽  
C. G. Moore
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Chain Molecules ◽  
Alkoxy Radicals ◽  
Full Extent ◽  
Carbon Chains ◽  
Butyl Peroxide ◽  
High Degree ◽  
Vulcanization Process

Abstract The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.

Kinetics of Internal Rotation of N,N-Dimethylacetamide: A Spin-Saturation Transfer Experiment

1997 ◽  
Vol 74 (8) ◽  
pp. 978 ◽  
Author(s):  
Russell L. Jarek ◽  
Robert J. Flesher ◽  
Seung Koo Shin
Keyword(s):  
Internal Rotation ◽  
Saturation Transfer ◽  
Transfer Experiment ◽  
Kinetics Of

Studies in the Vulcanization of Rubber. IV—A Theory of Vulcanization of Rubber

1930 ◽  
Vol 3 (4) ◽  
pp. 659-667
Author(s):  
G. R. Boggs ◽  
J. T. Blake
Keyword(s):  
Electrical Properties ◽  
Joule Effect ◽  
Vulcanized Rubber ◽  
Chemical Theory ◽  
Rubber Compounds ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization

Abstract A new theory has been advanced which, it is believed, explains completely the various phenomena connected with the vulcanization of rubber. It is entirely a chemical theory based on the existence of two separate and distinct rubber compounds, soft vulcanized rubber and ebonite. The theory explains satisfactorily the aging of rubber, the variation in combined sulfur at optimum cure caused by acceleration, the kinetics of vulcanization, the characteristics of various vulcanizing agents, the thermochemistry of vulcanization, the electrical properties of rubber, the reclaiming of rubber, and the Joule effect. A brief review and discussion of the phenomena and past theories of vulcanization have also been given.

Activity and conformational changes of horseradish peroxidase in trifluoroethanol

2002 ◽  
Vol 80 (2) ◽  
pp. 205-213 ◽  
Author(s):  
Hong-Wei Zhou ◽  
Yan Xu ◽  
Hai-Meng Zhou
Keyword(s):  
Enzyme Activity ◽  
Horseradish Peroxidase ◽  
Conformational Changes ◽  
Tertiary Structure ◽  
Polyacrylamide Gel Electrophoresis ◽  
Intrinsic Fluorescence ◽  
Two Phase ◽  
Main Effect ◽  
Α Helix ◽  
Kinetics Of

The effect of trifluoroethanol (TFE) on horseradish peroxidase (HRP) was determined using activity assay and spectral analysis including optical absorption, circular dichroism (CD), and intrinsic fluorescence. The enzyme activity increased nearly twofold after incubation with 5–25% (v/v) concentrations of TFE. At these TFE concentrations, the tertiary structure of the protein changed little, while small changes occurred at the active site. Further increases in the TFE concentration (25–40%) decreased the enzyme activity until at 40% TFE the enzyme was completely inactivated. The α-helix content of the protein increased at high TFE concentrations, while near-UV CD, Soret CD, and intrinsic fluorescence indicated that the tertiary structure was destroyed. Polyacrylamide gel electrophoresis results indicated that the surface charge of the enzyme was changed at TFE concentrations greater than 20%, and increasing concentrations of TFE reduced the enzyme molecular compactness. A scheme for the unfolding of HRP in TFE was suggested based on these results. The kinetics of absorption change at 403 nm in 40% TFE followed a two-phase course. Finally, HRP incubated with TFE was more sensitive to urea denaturation, which suggested that the main effect of TFE on HRP was the disruption of hydrophobic interactions.Key words: horseradish peroxidase, trifluoroethanol, unfolding, Soret.

Low-Temperature Set as a Measure of State of Vulcanization

1940 ◽  
Vol 13 (2) ◽  
pp. 222-234
Author(s):  
J. H. Fielding
Keyword(s):  
Low Temperature ◽  
Fundamental Property ◽  
Quantitative Measure ◽  
New Product ◽  
Temperature Behavior ◽  
Vulcanized Rubber ◽  
Scientific Equipment ◽  
Artificial Heat ◽  
Water Proof ◽  
High Degree

Abstract In his various patents on vulcanization, Charles Goodyear made several references to the change produced in the low-temperature behavior of rubber. In his earliest patent he stated that vulcanized rubber would not be “injuriously affected by exposure to cold”. The reissues of this patent stated the problem more clearly. “The leading object of my exertions was to render india-rubber capable of resisting the action of heat and cold within the range of atmospheric temperatures…. When compounded with sulfur, by the application of a high degree of artificial heat, I obtained good results, and when compounded with sulfur and the carbonate of lead I obtained the best results.”…. The new product “is water-proof, permanently and highly elastic under all conditions of its use”. Whether Goodyear was referring to the freezing of rubber under tension or under no tension we do not know, but it is probable that he had experienced both effects without distinguishing between them. It is interesting to find now that, one hundred years later, rubber chemists are still looking at this change in low-temperature behavior which he recognized as an effect of vulcanization, and are using the effect as a measure of degree of vulcanization. In recent years the T-50 test has gained considerable popularity as a quantitative measure of the tendency of rubber to freeze under tension. Its popularity is justified, since it can be applied over a broad range of cure and since it measures very precisely a seemingly fundamental property of rubber. It is, however, not the only means of expressing this effect quantitatively. The purpose of the present paper is to demonstrate a simpler method which yields surprisingly precise results, in spite of the fact that none of the usual scientific equipment is used and no measurements other than length measurements are required. Although other papers have approached this subject, none has as yet offered a simple substitute for T-50.

Sintering Kinetics of an Yttrium Aluminosilicate Glass

2012 ◽  
Vol 1475 ◽  
Author(s):  
Miguel O. Prado ◽  
Diana Lago ◽  
Diego S. Rodriguez
Keyword(s):  
Viscous Flow ◽  
Glass Powder ◽  
Glass Particle ◽  
Aluminosilicate Glass ◽  
Powder Size ◽  
Particle Volume ◽  
Sintering Kinetics ◽  
Nucleation Sites ◽  
Yttrium Disilicate ◽  
Kinetics Of

ABSTRACTYttrium aluminosilicate (YAS) glasses have been proposed as host matrices for the immobilization of radioactive elements. In addition, yttrium has been used to simulate actinides [1]. It is well known that these glasses are resistant to water corrosion and exhibit high Tg and good mechanical properties [2]. As shown in [3], on heating, yttrium disilicate and mullite / sillimanite crystals grow from the pre-existing nucleation sites on the surface, until each glass particle volume is fully crystallized (volume-homogeneous nucleation was not observed), decreasing the glassy surface available for sintering by viscous flow. Sintering takes place simultaneously, by viscous flow but competes with surface crystallization; thus, if thermal treatment is not carefully designed a vitroceramic is obtained. In this paper we study the isothermal sintering kinetics of a YAS glass-powder-size distribution and non-isothermal sintering kinetics at 1, 3, 5, 10 and 15 K/min of two YAS glass-powder-size distributions. From the experimental evidence obtained, and crystallization data from [3], we design a sintering procedure in order to achieve a high-density glass monolith with submicrometric crystalline phases.

Kinetics of Oil Sorption by Material Based on Leaf Litter

2019 ◽  
Vol 7 (2) ◽  
pp. 10-14
Author(s):  
А. Алексеева ◽  
A. Alekseeva ◽  
С. Степанова ◽  
S. Stepanova
Keyword(s):  
Leaf Litter ◽  
Heterogeneous Reactions ◽  
Desorption Process ◽  
Oil Sorption ◽  
Sorption Material ◽  
Material Contact ◽  
High Degree ◽  
Kinetics Of ◽  
Order Determination ◽  
Sorption Time

Studies of leaf litter as a sorption material with respect to oil at various temperatures have been carried out. It has been revealed that with process temperature increasing, the samples sorption capacity decreases. The oil sorption mechanism has been studied. It has been shown that the active sorption time was in the interval from 60 to 600 seconds. It has been proved that at the time of oil and sorption material contact for more than 600 seconds, the desorption process began. Kinetic dependencies of oil absorption by the proposed sorption material have been constructed and analyzed. The reaction order determination by a graphic method has showed that obtained functions with a high degree of correlation can be attributed to first-order heterogeneous reactions. Have been calculated thermodynamic parameters confirming the absence of a chemical reaction between oil and leaf litter. The carried out researches determine the most acceptable parameters of oil sorption by material based on leaf litter.

Kinetics of the reactive spreading of molten aluminum on ceramic surfaces

1995 ◽  
Vol 10 (3) ◽  
pp. 640-650 ◽  
Author(s):  
Douglas A. Weirauch ◽  
Willy M. Balaba ◽  
Anthony J. Perrotta
Keyword(s):  
Molten Aluminum ◽  
Unit Area ◽  
Triple Line ◽  
Temperature Analysis ◽  
Experimental Conditions ◽  
Ceramic Surfaces ◽  
Main Effect ◽  
Kinetics Of ◽  
Rate Of Movement

The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.

Rubber Elasticity and Gas Elasticity

1939 ◽  
Vol 12 (2) ◽  
pp. 124-129
Author(s):  
H. Mark
Keyword(s):  
Polyvinyl Alcohol ◽  
Room Temperature ◽  
Absolute Temperature ◽  
Rubber Elasticity ◽  
Chain Molecules ◽  
Internal Mobility ◽  
Higher Temperature ◽  
Coefficient Of Elasticity ◽  
Polyacrylic Ester ◽  
High Degree

Abstract All substances which are composed of long mobile chains show one peculiar property, highly reversible elasticity. Even though the range of temperature of this property may be notably variable (in the case of polyvinyl alcohol and rubber at about room temperature, in the case of polystyrene, sulfur, or Thiokol only at a higher temperature) still it is to be noted that for rubber-like elasticity the presence of long flexible chains is an indispensable factor. Thus, typical rubber elasticity occurs in polyvinyl alcohol (Vinarol), polybutadiene (Buna), polymethyl-butadiene (methyl rubber), polyacrylic ester and also in its mixed polymerisate with vinyl chloride. This type of elasticity occurs also in sinew fibrin and muscle fibrin, in polychlorobutadiene (Neoprene, Sovprene), in polyethylene sulfide (Thiokol, Baerite), polyphosphornitrile chloride and finally in vulcanized oils (factice) and also in elastic sulfur. In the cases so far examined (natural rubber, Buna, methyl rubber), it has been found that the coefficient of elasticity increases proportionally to the absolute temperature, and that during the stretching heat is evolved. This behavior is contrary to that of normal elastic materials, steel, quartz, glass, etc. It is striking that the substances which have this property of highly reversible (rubber-like) stretching are widely different chemically. This tempts one to ascribe that property to the similarity of their construction. For example, all the substances mentioned consist of long chain-molecules, which display a high degree of internal mobility. The number of members in these chains varies from 102 to 104 and their mobility is due to the kind of linkage between the members, mostly simple C—C bonds.

Sign in / Sign up

Export Citation Format

Share Document