Molecular motions and mechanical relaxation effects in atactic and isotactic polystyrenes at very low temperatures

Baccaredda, M.; Butta, E.; Frosini, Vittorio

doi:10.1002/pol.1965.110030307

Cited by 38 publications

(9 citation statements)

References 7 publications

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“…13 The β peak merges into the R peak at high frequencies. 2 Mechanical-relaxation 1 and NMR experiments 14 revealed additional γ and δ processes associated with oscillatory motions of the side phenyl groups. Quasielastic neutron scattering experiments 5 reveal also the existence of a rather fast relaxation process on the picosecond scale in the temperature range covering the glass-transition temperature.…”

Section: Introductionmentioning

confidence: 98%

“…Investigation of local dynamical properties of amorphous polymers has been a subject of many studies, both experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and by means of computer simulation. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Nevertheless, questions concerning mechanisms of segmental mobility in the vicinity of the glass transition still remain open.…”

Section: Introductionmentioning

confidence: 99%

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Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

2002

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Molecular dynamics simulations of bulk atactic polystyrene have been performed in a temperature range from 100 to 650 K at atmospheric pressure. Local translational mobility has been investigated by measuring the mean square translational displacements of monomers. The long-time asymptotic slope of these dependencies is 0.54 at T > Tg, showing Rouse behavior. Crossover from motion in the cage to Rouse-like dynamics has been studied at T > Tg with a characteristic crossover time follows a power law behavior as a function of T, as predicted by mode-coupling theory (MCT). We studied the coherent intermediate scattering function and show the agreement with scaling predictions of MCT. Local orientational mobility has been studied via the orientational autocorrelation functions, ACFs (Legendre polynomials of the first and second order), of both the main-chain and side-group bonds. The ACF relaxation times analysis shows strong coupling between the phenyl groups and the backbone relaxation. The relaxation times of the orientational R-relaxation follow the same power law (γ ∼ 2.9) as the characteristic translational diffusion time and the intermediate scattering function. Below Tg, both types of dynamics are described by the same activated law. The ACFs time-distribution functions reveal the existence of activated local rearrangements already above T g.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

2002

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“…4 This polymer has indeed been deeply studied by various techniques. From an experimental point of view, a large number of studies have been carried out by means of relaxation techniques, e.g., dielectric spectroscopy (DS), [5][6][7][8] dynamic mechanical analysis, [8][9][10][11] NMR, 12,13 and quasielastic neutron scattering. 14,15 From these researches, we can see that close to and below PS's glass transition temperature T g (∼370 K, the exact value depends on cooling rate and molecular weight distribution), 4,16 its precise viscoelastic behavior is determined by various relaxation processes, such as chain relaxation, segmental relaxation within a chain, and conformational transitions.…”

Section: Introductionmentioning

confidence: 99%

The influence of internal rotational barriers and temperature on static and dynamic properties of bulk atactic polystyrene

Xie

Qian

2012

The Journal of Chemical Physics

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We present molecular dynamics simulations of a chemically realistic model as well as a quasi-freely rotating chain model for bulk atactic polystyrene in a temperature range from 240 to 500 K to characterize the role of temperature and internal rotational barriers on static and dynamics properties of bulk polystyrene. We demonstrate that on different length scales, the change of structure shows different behavior upon cooling, and the internal rotational barriers play a similar role as temperature in this respect. We also show that larger plateau value of particle mean-squared displacement does not comply with the cage size predicted by the mode-coupling theory. It can be attributed to large steric hindrance between styrene units in the system. When the temperature is decreased, dynamic heterogeneity of conformational transition is found to become increasingly important for the conformational relaxation. Moreover, we have established a relation among the cage effect, the dynamic heterogeneity, and the conformational relaxation on the time scale of α- and β-relaxations.

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“…The specific location of each ring is given in Table 1. Reaction paths, energy profiles, and free energy barriers for ring rotation were calculated in each case, and rate constants were estimated using the elementary transition state theory rate expression:23 kBT l~AA\ zim *=irexplw) (10) All calculations were performed on SGI 4D/220 or IBM RISC/6000 workstations using our in-house modification of the CHARMM source code.42…”

Section: Methodsmentioning

confidence: 99%

A Study of Cooperative Phenyl Ring Flip Motions in Glassy Polystyrene by Molecular Simulations

Khare¹,

Paulaitis²

1995

Macromolecules

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Molecular motions and mechanical relaxation effects in atactic and isotactic polystyrenes at very low temperatures

Cited by 38 publications

References 7 publications

Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

The influence of internal rotational barriers and temperature on static and dynamic properties of bulk atactic polystyrene

A Study of Cooperative Phenyl Ring Flip Motions in Glassy Polystyrene by Molecular Simulations

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