Molecular dynamics simulation based evaluation of glass transition temperatures of polystyrene in the presence of carbon dioxide

Abstract

This paper develops a detailed molecular dynamics (MD) simulation model to study the glass transition temperature (T g ) of a finite polystyrene (PS) system in the presence of high pressure carbon dioxide (CO 2 ). Validated inter-atomic potentials for pure PS and CO 2 are used for these simulations. Specific parameters and combinations rules are introduced to accurately model the intermolecular interactions between PS and CO 2 . The intermolecular interaction model has a strong effect on the T g of the PS-CO 2 system. The MD model comprises PS and CO 2 molecules confined in a finite walled system to manifest the effects of high pressure CO 2 . The effectiveness of the simulation model is established by comparison with experimental free-volume data from positronium annihilation lifetime spectroscopy (PALS). An important outcome of this study is the identification of clearly demarcated regions for bulk and surface analysis. Physical properties such as density, free volume, segmental motion across the thickness and end group mobility are also studied to gain insight into the polymer dynamics. As is expected, the simulations show that the presence of high pressure CO 2 reduces the T g of PS significantly due to an increase in chain mobility. Additionally, the simulation data show a remarkable effect of CO 2 on the extent and characteristics of the surface layer.

Investigating the glass transition temperature at the atom-level in select model polyamides: A molecular dynamics study

“…This can manifest in a discontinuity at T g , a feature which has been demonstrated in numerous molecular dynamics [5,58] and experimental [58][59][60][61] studies. Experimentally this free volume can be measured using PALS [58,59,62] which have been shown to agree with FCV calculations through CESA. To determine if this characteristic is also apparent among these model polyamides, values of T g were extracted from a plot of FCV vs. temperature (see Figure 11).…”

Surface Effect on Mechanical Properties and Atomic Mobility of Ultrathin Polystyrene Films using Molecular Dynamics Simulations

“…A series of computational samples are created for PS thin films with different thicknesses using the augmented PCG scheme [20]. Periodic boundaries are applied for the two lateral directions and finite boundaries are applied for the thickness direction.…”

On the energy conservation during the active deformation in molecular dynamics simulations

“…The meanings of the variables and the values of the constant parameters can be found in the work by Srivastava et al (2010). A cutoff distance of 12 Å is used for the non-bonded interactions.…”

“…Initially the amorphous computational samples are generated using the augmented PCG scheme (Srivastava et al, 2010). The free-standing films are created with periodic boundaries along the two lateral directions and finite boundaries along the thickness direction, while the bulk samples are created with periodic boundaries along all three directions.…”