Effect of chemical structure on the isobaric and isochoric fragility in polychlorinated biphenyls

Roland, C. M.; Casalini, R.

doi:10.1063/1.1863173

Cited by 35 publications

(33 citation statements)

References 91 publications

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“…We analyzed the T and V dependences of the dielectric relaxation time for 14 materials, for which τ(T,P) and specific volumes (and thus the equation of state) have been reported; these materials were: poly(phenyl glycidyl ether)-co-formaldehyde (PPGE) [12], 1,1'-bis(p-methoxyphenyl)cyclohexane (BMPC) and 1,1'-di(4-methoxy-5-methylphenyl)cyclohexane (BMMPC) [13], salol [14], 1,2 polybutadiene (12PB) [15], polymethylphenylsiloxane (PMPS) and polymethyltolylsiloxane (PMTS) [16], phenylphthalein-dimethylether (PDE) [17], cresolphthalein-dimethylether (KDE) [18,19], polychlorinated biphenyls (PCB42 and PCB54) [20], propylene carbonate (PC) [21], polyvinylmethylether (PVME) [22], polyvinylacetate (PVAc) [23]. The original measurements (except for PVAc) were carried out either at the Naval Research Laboratory or Silesian University in Poland.…”

Section: Ii-results and Discussionmentioning

confidence: 99%

An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts

Casalini

Roland

2007

Journal of Non-Crystalline Solids

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A recently proposed expression to describe the temperature and volume dependences of the structural (or α-) relaxation time is discussed. This equation satisfies the scaling law for the relaxation times, ( ) ( )where T is temperature, V the specific volume, and γ a material-dependent constant. The expression for the functionis shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover, providing a description of the dynamics with a minimal number of parameters. The results herein can be reconciled with previously found correlations of the isochoric fragility with both the isobaric fragility at atmospheric pressure and the scaling exponent γ.

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Section: Ii-results and Discussionmentioning

confidence: 99%

An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts

Casalini

Roland

2007

Journal of Non-Crystalline Solids

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“…The only other requirement is knowledge of the EOS, which is deduced from the same PVT data yielding the scaling exponent. by weight chlorine) [38].…”

Section: Discussionmentioning

confidence: 99%

“…In Figures 2-4 experimental PVT data are plotted for three glass-formers [23,37,38], chosen because they span a range of γ. As can be seen, eq.…”

Section: Pressure Dependence Of T Gmentioning

confidence: 99%

Scaling of the local dynamics and the intermolecular potential

Roland

Feldman

Casalini

2006

Journal of Non-Crystalline Solids

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The experimental fact that relaxation times, τ, of supercooled liquids and polymers are uniquely defined by the quantity TV γ , where T is temperature, V specific volume, and γ a material constant, leads to a number of interpretations and predictions concerning the dynamics of vitrification. Herein we examine means to determine the scaling exponent γ apart from the usual superpositioning of relaxation data. If the intermolecular potential can be approximated by an inverse power law, as implied by the TV γ scaling, various equations are derived relating γ to the Grüneisen parameter and to a common expression for the pressure derivative of the glass temperature. In addition, without assumptions, γ can be obtained directly from pressure-volumetemperature data. These methods for determining γ from molecular or thermodynamic properties are useful because they enable the P-and V-dependences of τ to be obtained, and thereby various analyses of the dynamics to be explored, without the need to carry out relaxation measurements beyond ambient pressure.2

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“…[3][4][5][6]The exponent γ of the thermodynamic scaling also provides a measure of the relative importance of the density and temperature in controlling glassy dynamics. Hence, not surprisingly, a large body of experiments [7][8][9][10][11][12][13] and simulations [14][15][16][17][18][19][20] have probed the nature of thermodynamic scaling of glass-forming liquids since the first observation by Tölle et al for orthoterphenyl. [21] The existence of thermodynamic scaling is well established for as diverse materials as van der Waals liquids, polymers, ionic liquids, weakly hydrogen-bonded systems, etc.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

Freed

2013

The Journal of Chemical Physics

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Many glass-forming fluids exhibit a remarkable thermodynamic scaling in which dynamic properties, such as the viscosity, the relaxation time, and the diffusion constant, can be described under different thermodynamic conditions in terms of a unique scaling function of the ratio ρ γ /T , where ρ is the density, T is the temperature, and γ is a material dependent constant. Interest in the scaling is also heightened because the exponent γ enters prominently into considerations of the relative contributions to the dynamics from pressure effects (e.g., activation barriers) vs. volume effects (e.g., free volume). Although this scaling is clearly of great practical use, a molecular understanding of the scaling remains elusive. Providing this molecular understanding would greatly enhance the utility of the empirically observed scaling in assisting the rational design of materials by describing how controllable molecular factors, such as monomer structures, interactions, flexibility, etc., influence the scaling exponent γ and, hence, the dynamics. Given the successes of the generalized entropy theory in elucidating the influence of molecular details on the universal properties of glass-forming polymers, this theory is extended here to investigate the thermodynamic scaling in polymer melts. The predictions of theory are in accord with the appearance of thermodynamic scaling for pressures not in excess of ∼ 50 MPa. (The failure at higher pressures arises due to inherent limitations of a lattice model.) In line with arguments relating the magnitude of γ to the steepness of the repulsive part of the intermolecular potential, the abrupt, square-well nature of the lattice model interactions lead, as expected, to much larger values of the scaling exponent. Nevertheless, the theory is employed to study how individual molecular parameters affect the scaling exponent in order to extract a molecular understanding of the information content contained in the exponent. The chain rigidity, cohesive energy, chain length, and the side group length are all found to significantly affect the magnitude of the scaling exponent, and the computed trends agree well with available experiments. The variations of γ with these molecular parameters are explained by establishing a correlation between the computed molecular dependence of the scaling exponent and the fragility. Thus, the efficiency of packing the polymers is established as the universal physical mechanism determining both the fragility and the scaling exponent γ.

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Effect of chemical structure on the isobaric and isochoric fragility in polychlorinated biphenyls

Cited by 35 publications

References 91 publications

An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts

An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts

Scaling of the local dynamics and the intermolecular potential

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

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