Structure factors in polystyrene: a neutron scattering and MD-simulation study

Aramendia, Iñigo; Álvarez, F.; Colmenero, Juan; Arbe, Arantxa

doi:10.1016/j.physb.2004.03.228

Cited by 29 publications

(39 citation statements)

References 3 publications

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“…To do this, we simply divide the carbon atoms into two groups: the carbons in phenyl rings (PRC) and the carbons in main chain (MCC) and calculate their respective correlations. 48 From Fig. 1(b), we can find that the first peak at 0.6 Å −1 is mainly due to MCC-MCC correlations and the PRC-PRC correlations are responsible for the second peak centered at about 1.3 Å −1 .…”

Section: B Static Propertiesmentioning

confidence: 82%

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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Section: B Static Propertiesmentioning

confidence: 82%

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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“…The complementary use of these techniques has proven to be an extremely successful route to address a number of similar problems in the field of soft matter. 7,[27][28][29][30][31][32][33][34][35][36][37][38][39] Regarding MD simulations on PEO, a relatively large number of publications can be found in literature. 25,26,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]60 Some of them deal mainly with structural properties, 48,50,51,[53][54][55][56]60 but the local dynamics is also addressed in others; 42,52,57 sometimes the works have been motivated by its use as polyelectrolyte 40,41,…”

Section: Introductionmentioning

confidence: 99%

Study of the dynamics of poly(ethylene oxide) by combining molecular dynamic simulations and neutron scattering experiments

Brodeck

Álvarez

Arbe

et al. 2009

The Journal of Chemical Physics

128

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We performed quasielastic neutron scattering experiments and atomistic molecular dynamics simulations on a poly(ethylene oxide) (PEO) homopolymer system above the melting point. The excellent agreement found between both sets of data, together with a successful comparison with literature diffraction results, validates the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field used to produce our dynamic runs and gives support to their further analysis. This provided direct information on magnitudes which are not accessible from experiments such as the radial probability distribution functions of specific atoms at different times and their moments. The results of our simulations on the H-motions and different experiments indicate that in the high-temperature range investigated the dynamics is Rouse-like for Q-values below approximately 0.6 A(-1). We then addressed the single chain dynamic structure factor with the simulations. A mode analysis, not possible directly experimentally, reveals the limits of applicability of the Rouse model to PEO. We discuss the possible origins for the observed deviations.

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“…This can be done considering the inter-chain distance for the investigated glass-forming polymers, which can be obtained from the static structure factor S(Q). Values for this distance can be calculated from the available measurements of the static structure factor of PS [26,27], PVAc [25] and PVME [28], being the resulting values: d PS = 9Å, d PVAc = 8.4Å and d PVME = 6.3Å. It is noteworthy that the diameters of CRR found at T g for these polymers are almost quantitatively twice the corresponding intermolecular distance, suggesting that the cooperative rearrangement only involves the first shell around a basic structural unit.…”

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confidence: 99%

Route to calculate the length scale for the glass transition in polymers

2007

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The occurrence of glass transition is believed to be associated to cooperative motion with a growing length scale with decreasing temperature. We provide a novel route to calculate the size of cooperatively rearranging regions CRR of glass-forming polymers combining the Adam-Gibbs theory of the glass transition with the self-concentration concept. To do so we explore the dynamics of glass-forming polymers in different environments. The material specific parameter α connecting the size of the CRR to the configurational entropy is obtained in this way. Thereby, the size of CRR can be precisely quantified in absolute values. This size results to be in the range 1 ÷ 3 nm at the glass transition temperature depending on the glass-forming polymer.PACS numbers: 64.70. Pf, 83.80.Tc, 83.80.Rs, 77.22.Gm The nature of the glass transition is one of the most important unsolved problems in condensed matter physics and research in this field has enormously intensified in the last decades due to its strong fundamental as well as applicative implications. Among the peculiar phenomena displayed by glass-forming liquids, the super-Arrhenius temperature dependence of the viscosity and the structural correlation time is certainly one of the most intriguing. In this framework, more than forty years ago Adam and Gibbs [1] theorized that such a pronounced temperature dependence of the structural correlation time is due to a cooperative process involving several basic structural units forming cooperatively rearranging regions (CRR), which size increases with decreasing temperature. Since then a great deal of theoretical approaches [2,3] as well as simulation studies [4] and very recently experimental studies employing multipoint dynamical susceptibilities [5] have been devoted in the search of good candidates for CRR as well as its size and temperature dependence. All of these studies suggest that a growing correlation length with decreasing temperature of the order of several nanometers exists. According to the Adam-Gibbs (AG) theory of the glass transition, the increase of the structural relaxation time with decreasing temperature, accompanied by the growth of the cooperative length scale, is due to the decrease of the number of configurations the glassformer can access, namely the configurational entropy (S c ) of the system. The connection between the structural relaxation time and S c is expressed by [1]:where C is a glass-former specific temperature independent parameter and τ 0 is the pre-exponential factor. The dynamics of a large number of glass forming systems have been successfully described through the AG equation in both experiments for low molecular weight glass formers [6] and polymers [7], as well as simulations [8]. Apart from the relation between the relaxation time and the configurational entropy, the AG theory provides a connection between the number of basic structural units belonging to the CRR and the configurational entropy: N ≈ S −1 . Several recent simulations studies, where the cooperative length scale and...

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Structure factors in polystyrene: a neutron scattering and MD-simulation study

Cited by 29 publications

References 3 publications

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

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

Study of the dynamics of poly(ethylene oxide) by combining molecular dynamic simulations and neutron scattering experiments

Route to calculate the length scale for the glass transition in polymers

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