Variation of the Effective Activation Energy Throughout the Glass Transition

Vyazovkin, Sergey; Sbirrazzuoli, Nicolas; Dranca, Ion

doi:10.1002/marc.200400268

Cited by 77 publications

(67 citation statements)

References 40 publications

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“…dielectric and mechanical spectroscopy, for the α-relaxation [44,46]. Of course, one should not expect precise agreement between the absolute values.…”

Section: Isoconversional Treatmentmentioning

confidence: 96%

“…In Eq. 3.21, z * is inversely proportional to the configurational entropy that increases with T so that both z * and the effective activation energy (i.e., z * Δμ) decrease with T. Note that even before the first applications [30,46] of isoconversional methods to the glass transition kinetics, the trend for the activation energy to decrease with increasing temperature was observed in other studies [47][48][49]. In them, the activation energy was determined from the shift in the value of T g with the heating rate in accord with the equation proposed by Moynihan et al: [42,43] (3.…”

Section: Isoconversional Treatmentmentioning

confidence: 98%

“…3.14). Figure 3.17 presents a set of the E versus T dependencies evaluated by applying an isoconversional method to the glass transition in a series of substances: poly(vinyl chloride) (PVC), poly( n-butyl methacrylate) (PBMA), PVP, poly(ethylene 2,6-naphthalate) (PEN), PS, poly(ethylene terephthalate) (PET), and boron oxide (B 2 O 3 ) [44,46]. The differences in the activation energy variability are really staggering.…”

Section: Isoconversional Treatmentmentioning

confidence: 99%

See 2 more Smart Citations

Physical Processes

Vyazovkin

2015

Isoconversional Kinetics of Thermally Stimulated Processes

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“…dielectric and mechanical spectroscopy, for the α-relaxation [44,46]. Of course, one should not expect precise agreement between the absolute values.…”

Section: Isoconversional Treatmentmentioning

confidence: 96%

Section: Isoconversional Treatmentmentioning

confidence: 98%

Section: Isoconversional Treatmentmentioning

confidence: 99%

See 1 more Smart Citation

Physical Processes

Vyazovkin

2015

Isoconversional Kinetics of Thermally Stimulated Processes

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“…17 The increase in E at higher conversions for the system can be understood in terms of cooperative motion of the chain segments. 18 At the early stages of the transition, the packing is loose, which allows the chain segments to move independently (i.e., with a lower degree of cooperativity). As the cure reaction proceeds, the free volume decreases.…”

Section: Mechanism and Kinetics Of Epoxy-imidazole Cure Studied With mentioning

confidence: 99%

Mechanism and Kinetics of Epoxy-Imidazole Cure Studied with Two Kinetic Methods

Zhou

Jin

et al. 2005

Polym J

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ABSTRACT:Curing kinetics and mechanism of the diglycidyl ether of bisphenol-A (DGEBA) initiated with 2-ethyl-4-methylimidazole (EMI-2,4) were studied with two methods by using differential scanning calorimetry (DSC). Method I and Method II were deduced by assuming a constant E and a variable E, respectively. With Method I, the cure reaction activation energy E, the frequency factor A and the overall order of reaction m þ n are calculated to be 49.03 KJ mol À1 , e 14:5 and 1.22, respectively. With Method II, E is proved to decrease initially, and then increase as the cure reaction proceeds, and the value of E spans from 34.3 to 63.84 KJ mol À1 . The variations of E were also used to study the cure reaction mechanism. Method I and Method II are effective as long as they are used in proper aspects. With these two methods used all together, we can have a comprehensive and in-depth understanding of the cure reactions, such as those of the DGEBA/EMI-2,4 system. [DOI 10.1295/polymj.37.833] KEY WORDS Cure Reaction / DSC / Kinetic Method / DGEBA/EMI-2,4 System / Imidazole-cured resins are widely used in the electronics industry as molding and sealing compounds because they exhibit a better heat resistance, a higher modulus, and a wider range of cure temperatures than amine-cured systems. The kinetics of imidazole/resin systems has been widely studied by using isothermal or dynamic DSC technique. [1][2][3][4][5] But their studies were all based on the assumption of a constant E and the whole reaction of curing was considered as a single kinetic process (Method I). Therefore, the calculated E is the apparent activation energy of the global reaction. However, the reaction of curing epoxy resins is normally very complex, such as the change from chemical kinetic control to diffusion control in the advance of the curing, 6,7 and E changed momently. In this work, another method deduced without the assumption of constant E (Method II) was also employed to analyze the dynamic DSC data, then the interpretation of the dependence of E on the extent of reaction in the terms of the reaction mechanisms was also made. As a result, with these two different kinetic methods, which have their particular merits and demerits, used together, we can have a comprehensive and in-depth understanding of the curing kinetics of the DGEBA/EMI-2,4 system. EXPERIMENTALEpoxy resin used in this work was a nominally difunctional epoxy resin, Epon 828 supplied by Shanghai Resin Co. Epon 828 is, basically, DGEBA with the epoxy value of 0.48-0.52 mol/100 g. The structure for DGEBA is shown in Figure 1. The curing agent used was EMI-2,4 supplied by Beijing Chemical Reagent Co. Other agents used were analytically pure grade and were supplied by Beijing Chemical Reagent Co.Approximately 10 mg sample of the mixture of DGEBA and EMI-2,4 was weighed accurately into an aluminum DSC sample pan and then covered with an aluminum lid. The entire operation was carried out in a dry chamber. DSC measurements were carried out by using a Perkin-Elmer DSC-7 system. The DSC ...

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“…In the first set of runs the activation energy is derived from the shift of annealing peaks generated in the sub-T g region. In the second set, the activation energy is evaluated by applying an advanced isoconversional method to the glass transition step (4). In this paper the aforementioned approach is applied to the relaxation of two carbohydrates: glucose and maltitol.…”

Section: Introductionmentioning

confidence: 99%