Crystallization in Stretched Polymer Networks. II. trans-Polyisoprene

1967 ◽  
Vol 40 (5) ◽  
pp. 1394-1408
Author(s):  
A. N. Gent
Keyword(s):  
Tensile Stress ◽  
Melting Temperature ◽  
Satisfactory Agreement ◽  
Polymer Networks ◽  
Crystal Forms ◽  
Melting Temperatures ◽  
Test Pieces ◽  
Oriented Crystallization ◽  
Crystal Melting ◽  
Large Contraction

Abstract Measurements are described of the rates of crystallization and crystal melting temperatures in stretched test pieces of trans-polyisoprene, crosslinked to various degrees. The increases in rate with extension are attributed to the corresponding increases in melting temperature and hence degree of supercooling. The rise in the melting temperature of both the α and β crystal forms is found to be in satisfactory agreement with Flory's treatment of oriented crystallization. Changes in tensile stress are also generally in accord with the formation of oriented crystallites. For the more lightly crosslinked materials, a pronounced rise in tensile stress occurred during the later stages of crystallization, at extensions below about 100 per cent. Reasons are given for attributing this phenomenon primarily to the relatively large contraction in volume on crystallization, rather than to the formation of folded-chain crystallites.

Crystallization in Stretched Polymer Networks. I. trans-Polychloroprene

1967 ◽  
Vol 40 (4) ◽  
pp. 1071-1083 ◽  
Author(s):  
A. N. Gent
Keyword(s):  
Melting Temperature ◽  
Polymer Networks ◽  
Crystal Form ◽  
Simple Extension ◽  
Theoretical Treatment ◽  
Nucleation Kinetics ◽  
Segmental Mobility ◽  
Melting Temperatures ◽  
Direct Measurements ◽  
Stress Changes

Abstract Changes in tensile stress afford a simple means of studying the rates of crystallization and the melting temperatures in crosslinked polymers subjected to simple extension. The form and magnitude of the stress changes in networks of trans-polychloroprene are closely similar to those observed for cis-1:4-polyisoprene and cis-l:4-polybutadiene networks. They are in accord with the formation of oriented crystallites and incompatible with folded chain crystallization at extensions as low as 15 per cent. It seems likely that the present networks do not crystallize by chain folding even in the unstretched state. The large increases in rate of crystallization with extension are approximately accounted for by corresponding increases in the equilibrium melting temperature. Direct measurements of the melting temperature show similar rises with extension. The rise in melting temperature is in good agreement with Flory's theoretical treatment of oriented crystallization at extension ratios of three and higher (when the crystallite orientation is complete) for three networks having different degrees of crosslinking. When referred to a constant segmental mobility, namely, that obtaining at Tg+50° C, the rates of crystallization at various extensions obey a common dependence upon the degree of supercooling. This relation is in fair accord with theories of nucleation kinetics, except at the lowest temperatures where there is some indication of the appearance of a new crystal form.

Impact of dynamic covalent chemistry and precise linker length on crystallization kinetics and morphology in ethylene vitrimers

Soft Matter ◽  
2022 ◽  
Author(s):  
Bhaskar Soman ◽  
Yoo Kyung Go ◽  
Chengtian Shen ◽  
Cecilia Leal ◽  
Christopher M. Evans
Keyword(s):  
Crystal Structure ◽  
Melting Temperature ◽  
Crystallization Kinetics ◽  
Polymer Networks ◽  
Exchange Reactions ◽  
Dynamic Covalent Chemistry ◽  
Linker Length

Vitrimers, dynamic polymer networks with topology conserving exchange reactions, can lead to unusual evolution of the melting temperature and crystal structure of ethylene networks.

Studies on the Melting of DNA

1974 ◽  
Vol 29 (3-4) ◽  
pp. 130-132
Author(s):  
Gokul Chandra Das
Keyword(s):  
Ionic Strength ◽  
Melting Temperature ◽  
Thermal Denaturation ◽  
Spectrophotometric Methods ◽  
Melting Temperatures

Abstract The thermal denaturation of the native DNA in solvents of varying salt concentrations was studied by viscometric and spectrophotometric methods. It was observed that within the molarity range of 0.02 ᴍ to 0.3 ᴍ, the melting temperatures obtained by the two independent methods agreed well, but that at lower ionic strength the agreement was not satisfactory. Both the visco­metric and the spectrophotometric measurements showed an increase of the melting temperature with increasing counterion concentration and a levelling off effect in the neighbourhood of 0.3 ᴍ.

The Pressure of CO2 Crystal Melting Temperature Dependence

2014 ◽  
Vol 887-888 ◽  
pp. 935-938
Author(s):  
Shuai Zhang ◽  
Lei Chen ◽  
Zhi Shuai Wu ◽  
Shang Wu Hou
Keyword(s):  
Phase Transition ◽  
Temperature Dependence ◽  
Melting Temperature ◽  
Order Phase Transition ◽  
Melting Curve ◽  
Clapeyron Equation ◽  
First Order ◽  
First Order Phase Transition ◽  
Crystal Melting ◽  
First Order Phase

This paper is based on the CO2crystal as an example, through the two reasonable simplification ΔH(T,P) ΔH(T) and ΔV(T,P) ΔV(P) into the Clapeyron equation to calculate the melting curve. Because the Clapeyron equation can describe all the first-order phase transition, accordingly it is determining the material T-P diagram provides a new way.

The Attack of Ozone on Stretched Rubber Vulcanizates. II. Conditions for Cut Growth

1960 ◽  
Vol 33 (4) ◽  
pp. 1156-1165
Author(s):  
M. Braden ◽  
A. N. Gent
Keyword(s):  
Experimental Study ◽  
Tensile Stress ◽  
Natural Rubber ◽  
Critical Value ◽  
Rubber Sheet ◽  
Test Pieces ◽  
Rubber Vulcanizate ◽  
Present Part ◽  
Applied Tensile Stress ◽  
Made In

Abstract In Part I an experimental study was reported of the factors determining the rate of propagation of a cut through a stretched rubber sheet under the action of an atmosphere containing ozone. It was remarked that no growth took place from a small razor cut made in one edge of the test pieces unless a critical value of the applied tensile stress was exceeded. The value was quite small, of the order of 100 g/cm2 for a soft natural rubber vulcanizate. In the present part an examination is reported of the conditions necessary for a crack to form or, being present, to grow.

Analysis of structures and melting properties of the 19-atom Ni–Co clusters

2014 ◽  
Vol 28 (25) ◽  
pp. 1450171 ◽  
Author(s):  
Shi-Wei Ren ◽  
Jing-Wei Sun ◽  
Yan-Zhong Hao
Keyword(s):  
Melting Temperature ◽  
Nickel Atom ◽  
Melting Temperatures ◽  
Pure Cobalt ◽  
Melting Phenomenon ◽  
Nickel Clusters ◽  
Melting Properties ◽  
Mixed Clusters ◽  
Dynamics Method ◽  
Cobalt And Nickel

In this paper, by using the classical molecular dynamics method and the GEAM potential, the geometric structure and the melting properties of the 19-atom Ni – Co clusters with different compositions are studied. It is found that all the clusters have the double icosahedron structures although some of the structures are slightly deformed. With the increase of the temperature, a pre-melting phenomenon is observed. The pre-melting temperatures of the pure cobalt and nickel clusters are very close. But on the whole, the pre-melting temperature decreases with the increase of the number of the nickel atom for the mixed clusters. The effects of the substitution atoms on the melting temperature of the clusters are similar to that on the pre-melting temperature although there are some oscillations in the decrease process. The mechanism of these findings are also investigated and analyzed.

Thermodynamics of Crystallization in High Polymers. Natural Rubber

1955 ◽  
Vol 28 (3) ◽  
pp. 718-727 ◽  
Author(s):  
Donald E. Roberts ◽  
Leo Mandelkern
Keyword(s):  
Natural Rubber ◽  
Melting Temperature ◽  
Low Temperatures ◽  
Rapid Heating ◽  
Heat Of Fusion ◽  
Low Molecular Weight ◽  
Heating Rates ◽  
Equilibrium Melting Temperature ◽  
Clapeyron Equation ◽  
Melting Temperatures

Abstract The existence of an equilibrium melting temperature, T0m, at 28 ± 1°, for unstretched natural rubber has been established, using dilatometric methods. The lower melting temperatures previously observed are a consequence of the low temperatures of crystallization and the rapid heating rates employed. From melting point studies of mixtures of the polymer with low molecular-weight diluents, the heat of fusion per repeating unit, ΔHu has been evaluated as 15.3 ± 0.5 cal./g. The values of ΔHu and T0m have then been combined with data of other workers to obtain the following information concerning natural rubber: (1) The variation of melting temperature with applied hydrostatic pressure has been calculated from the Clapeyron equation to be 0.0465° C/atm. (2) The degree of erystallinity resulting from maintaining a sample at 0° until the rate of crystallization is negligible has been calculated, by three independent methods, to be in the range 26 to 31 per cent. (3) Analysis of the stress-strain-temperature relationship has indicated that crystallization is the cause of the large internal energy changes that are observed at relatively high elongations.

Effect of Al2O3 and CaF2 on Melting Temperature of High Calcium Ladle Desulfurization Slag

2015 ◽  
Vol 1094 ◽  
pp. 325-328
Author(s):  
Wei Fan ◽  
Jin Zhu Zhang ◽  
Wan Zhong Ao ◽  
Jun Huang
Keyword(s):  
Melting Temperature ◽  
Orthogonal Design ◽  
Molten Iron ◽  
Iron And Steel ◽  
Melting Temperatures ◽  
High Calcium ◽  
Analytical Reagent ◽  
The Impact

The external desulphurization of molten iron has become an important step in the production of steel and iron. The melting temperatures of high calcium desulfurization slag, which were taken from Shougang Shuicheng Iron and Steel (Group) Co. Limited, were investigated on basis of the method of hemisphaerium temperature. The contents of CaO, Al2O3 and CaF2 in the slag were adjusted in 47%-53%, 14%-20% and 2%-10% respectively by adding analytical reagent Ca (OH)2, Al2O3 and CaF2 using orthogonal design. The results show that the melting temperature of desulfurization slag decreases obviously with the increase of the content of Al2O3 between 14% and 20%, and decreased markedly with the increase of the content of CaF2 lower than 8%. The impact to the melting temperature of the high calcium slag is as follows: Al2O3 > CaF2 > CaO.

scholarly journals Studying the Effects of Vacancies on the Melting Temperature of \(\text{AgCe}\) Alloy

2018 ◽  
Vol 28 (2) ◽  
pp. 155
Author(s):  
Dang Thanh Hai ◽  
Vu Van Hung ◽  
Giang Thi Hong
Keyword(s):  
High Pressure ◽  
Free Energy ◽  
Melting Temperature ◽  
Moment Method ◽  
Statistical Moment ◽  
Melting Temperatures ◽  
Substitution Alloy ◽  
Numerical Calculation Method ◽  
Analytical Expressions ◽  
Statistical Moment Method

In order to evaluate the effects of vacancies on the melting temperature of AgCe alloy, the statistical moment method was used to find out the analytical expressions to determine the Gibbs free energy in the AB substitution alloy and the expression to calculate the melting temperature of perfect and imperfect AB substitution Alloys. The melting temperature was calculated by the numerical calculation method on the perfect and imperfect AgCe alloy. The calculating results shown that the melting temperature of alloys increase with a increase in pressure. The melting temperatures of imperfect alloy of AgCe, Ag2Ce and Ag3Ce are always slightly lower than that of perfect alloys. Especially, the melting temperatures value of perfect and imperfect alloy were almost the same at high pressure. The melting temperature of alloys increase with an increase in amount of Ag containing in the alloys. The calculated results agreed well with the experimental results at P = 0.

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