Structural Relaxation of Glass-Forming Polymers Based on an Equation for Configurational Entropy. 2. Structural Relaxation in Polymethacrylates

Ribelles, J. L. Gomez; Pradas, Manuel Monleón; Vidaurre, Ana; Colomer, F. Romero; Estellés, Jorge Más; Dueñas, José María Meseguer

doi:10.1021/ma00121a026

Cited by 54 publications

(43 citation statements)

References 12 publications

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“…More equations and variables, and hence matters to be attended to, appear in the whole theory for the model to reproduce DSC curve (see ref [7][8][9]15 and references cited therein), where the Tool-NarayanaswamyMoynihan approach is the basic grounds. 20,21 The non-exponentiality of the relaxation can be written by the stretched exponential form with the shape parameter of (0 < 1).…”

Section: Discussionmentioning

confidence: 99%

“…In deriving eq 6, Ribelles et al employ reduced time 24 to write the elapsed time t. 8,9 However, the expression of summation was shown here in order to emphasise the practical equation used in the calculation. If the limit state of the structural relaxation process would coincide with the extrapolation of the equilibrium values determined at temperatures above the glass transition, S c lim ðTÞ ¼ S c eq ðTÞ could be given with,…”

Section: Discussionmentioning

confidence: 99%

“…Values obtained for PCBA6 were in the same order as those reported for poly(butyl methacrylate) (T g ¼ 310 K) and PMA4. 9,34 The curves are almost indistinguishable in the narrow temperature range around T g , which range is sensitive in calculating the c p (T) curve.…”

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confidence: 97%

“…Afterwards, another model was proposed in reproducing DSC curve on the basis of the configurational entropy; here this is called as SC model. [8][9][10][11][12][13] The basic feature which is common to both models is the application of Boltzmann superposition principle, which enables to calculate the quantities of the state corresponding to the thermal history the polymer had experienced.These two models currently accompany several variations to predict DSC results accurately. 7,[14][15][16] The arguments are taken on the equation to define .…”

mentioning

confidence: 99%

“…SC model analysis without using the parameter has also been reported for the three kinds of polymethacrylate. 9 However, the introducing in SC model can be seen in almost all the modelling studies reported concerning the enthalpy relaxation of polymer. 8,10,11,[13][14][15]34 The proposed measure for the structural relaxation of PCBA6 is the value of as mentioned in the introduction section.…”

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confidence: 99%

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Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Analysis based on Configurational Entropy Model with the AG Expression

Tanaka

2009

Polym. J.

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The enthalpy relaxation of poly(cyanobipheny hexylacrylate) has been studied by differential scanning calorimetry. The experimental results of the heat capacity (c p ) were compared with the prediction of a phenomenological model for the process of structural relaxation based on the configurational entropy (S c ) and the relaxation time expressed by the Adam-Gibbs equation. This model follows the evolution of the configurational entropy of the sample during the whole thermal history including an isothermal annealing. The parameters of the model were calculated by simultaneous fits to the experimental results. With the calculation result, the peak position appeared in DSC curve of c p was interpreted using the plot of temperature dependence of S c . The plot showed that S c rapidly approached to the configurational entropy of equilibrium (S c eq ) in the narrow temperature range around T g , which is often referred to as the recovery of enthalpy, and thus the recovery of S c , in interpreting the enthalpy relaxation. As the measure of structural relaxation upon the isothermal ageing, the value of relaxation function () was considered, which estimates the departure from the equilibrium. The correlation between of S c and of enthalpy is also presented. The physical properties of the liquid crystalline polymer with cyanobiphenyl groups in the side chain (PCBA) have been studied with respect to the effects of molecular weight and spacer length.1,2 In the previous paper, the enthalpy relaxation measured using Differential Scanning Calorimetry (DSC) was analysed with the activation energy spectrum (AES) model. 3This model provides information about thermally activated processes which are available to contribute to observed changes in the properties upon physical ageing. For the enthalpy relaxation of PCBA6 (PCBA in which the spacer length is 6), the analysis gives the relation between the process number and the activation energy, in other words, the distribution of the relaxation process.In general, the decrease in enthalpy upon the isothermal ageing at temperature below the glass transition temperature T g , is closely related to the structural relaxation toward equilibrium in the glassy state. Concerning the relaxation of PCBA6, the optical texture was shown to vary in the previous paper, as an evidence of structural change. The change in optical texture is being considered as the coarsening dynamics of the disclinations. That is to say, the dynamics of PCBA6 molecules bring about the change in structure.On the other hand, the modelling approaches for enthalpy relaxation of polymer have been reported, which attempts to reproduce the measured DSC curve using quantities of state. The quantities of state employed are the configurational entropy, S c , and the fictive temperature, T f . 4,5 It has been shown that the main features of the relaxation process can be modelled on the basis of a distribution of relaxation times that depends both on the temperature and on the structure of the material represented by the value o...

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