A molecular dynamics simulation study of the α- and β-relaxation processes in 1,4-polybutadiene

Coincident Correlation between Vibrational Dynamics and Primary Relaxation of Polymers with Strong or Weak Johari-Goldstein Relaxation

“…The analysis in terms of a sum of two stretched exponential decays, Equation (5) and Equation (6), conforms with most studies of primary and secondary relaxations in MD simulation [13][14][15]30,31] and in some experiments done in time domain [32,33]. Then, it facilitates the comparison between our results to those present in literature.…”

Secondary Johari–Goldstein relaxation in linear polymer melts represented by a simple bead-necklace model

“…We have shown previously that the decay of the TACF in PBD closely reflects segmental relaxation as probed by dynamic neutron scattering [15,16], NMR T 1 relaxation [17], and dielectric relaxations [18]. We also showed that in simulations of freely-rotated and lower-barrier PBD, where a clear separation of α-and β-relaxations has been observed, the corresponding relaxation times for these processes obtained from TACF, dipole moment autocorrelation function, and incoherent dynamic structure factor were very similar [6][7][8]; further illustrating that the TACF is a representative characteristic of segmental relaxation in polymeric systems.…”

“…Nevertheless, in our recent works [6][7][8] we demonstrated that reduction or elimination of dihedral barriers in PBD significantly reduces glass transition of this polymer and promotes the separation between α-and β-relaxations allowing the observation of two wellseparated relaxations on time scales accessible to MD simulations (less than a microsecond). Extensive simulations of melts [6][7][8] and blends [8][9][10] comprised of PBD chains with reduced dihedral barriers allowed us for the first time to use MD simulations to systematically investigate the mechanisms of the β-relaxation and its correlation with the α-relaxation as a function of thermodynamic conditions.…”

“…Extensive simulations of melts [6][7][8] and blends [8][9][10] comprised of PBD chains with reduced dihedral barriers allowed us for the first time to use MD simulations to systematically investigate the mechanisms of the β-relaxation and its correlation with the α-relaxation as a function of thermodynamic conditions. While these works provided a great insight into understanding of secondary relaxations it is hard to determine which of the observed mechanisms/correlations are a generic characteristic of the β-relaxation and which are specific for the investigated polymer.…”

Relationship between the α‐ and β‐relaxation processes in amorphous polymers: Insight from atomistic molecular dynamics simulations of 1,4‐polybutadiene melts and blends

“…To create melts with faster dynamics, the rotational energy barriers for all backbone dihedrals (except for double bonds) were reduced by a factor of four relative to the CR-PBD model yielding the low barrier, or LB-PBD, model. 12 For example in Figure 2, we compare the dihedral energy profiles for the CR-PBD and LB-PBD models for the backbone C(sp 2 )À ÀC(sp 3 )À ÀC(sp 3 )À ÀC(sp 2 ) (alkyl) dihedrals. The choice of this scaling was motivated by our desire to move the bifurcation of the a-relaxation and b-relaxation processes into an accessible time window, as was found in simulations of a 1,4-polybutadiene (PBD) model with no dihedral barriers, 13 while at the same time maintaining clearly identifiable conformation states corresponding to those found in CR-PBD.…”