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

Abstract

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.

Molecular dynamics simulation study of glass transition in hydrated Nafion

“…The results obtained from MD simulation by Harmandaris et al show the increasing effect of elevated pressure on glass transition temperature, which is in agreement with experimental measurements . Xie et al in 2012 investigated the effect of polymer backbone stiffness on the static and dynamic properties . This effect was also investigated in another study by Bulacu and Giessen within a coarse grain model .…”

“…The newly proposed multiple shape memory properties of Nafion, which is accompanied by thermal phase transitions, is another example that shows the importance of investigations of thermomechanical properties and glass transition temperature at the microscopic level . Shape memory materials can be adjusted to memorize certain temporary shapes, which had been imposed during a shape fixing process and recover their permanent shape upon applied stimulus such as electric field, heat, or light.…”

Structural characteristics of a cooperatively rearranging region during the glass transition of a polymer system

“…42 By using the single-molecule uorescence microscopy, Wöll's group found that the temperature dependence of fraction of mobile molecules in polystyrene lms exhibited similar trends with that of PSM. [26][27][28][29][30][31][32] Similarly, we also observe the conformational changes during cooling in the current simulation. [26][27][28][29][30][31][32] Similarly, we also observe the conformational changes during cooling in the current simulation.…”

“…13,14 For instance, the structural characteristics of CRR are still unknown. [27][28][29][30][31][32] The increase of the fraction of transconformations may induce the formation of the short-range order in polymers. For colloidal system, Tanaka et al 23,24 and Yodh et al 25 detected the formation of some local ordered structures during cooling, and they argued that the development of the local ordered structures may be the origin of the slow dynamics.…”

Simulated Dilatometry and Static Deformation Prediction of Glass Transition and Mechanical Properties of Polyacetylene and Poly(para‐phenylene vinylene)

“…At the glass transition temperature, the specific volume, v , versus temperature, T , exhibits a change in slope, moving from a low value in the glassy state ( T < T g ) to a higher value in the rubbery state ( T > T g ) . Molecular dynamics can be used to determine the specific volume of the polymer at different temperatures, at a constant pressure.…”