Spatial Density Correlation in Polymer Melts†

doi:10.7503/cjcu20180626

Abstract

Abstract:

The spatial density correlation in glass-forming polymer melt with different chain architectures was investigated using molecular dynamics simulation. The local environment of each bead was identified. Using the Voronoi construction, the results indicate that the chain ends have more local volume in the average level and the mobility of chain ends is higher. Moreover, the distributions of local volume become narrow when decreasing temperature and the rescaled distributions follow a master curve, implying that the melts have qualitatively similar amorphous structure for different chain architectures. The loosely and densely packed particles were identified according to their local volume. Both loosely and densely packed particles tend to form clusters, and the loosely packed particles was larger than that by densely packed particles. The simulation results demonstrate the spatial correlation of loosely packed particles is stronger, which might help to understand the glass forming behavior of polymer melts.

Key words: Spatial density correlation, Glass-forming polymer melt, Molecular dynamics simulation

CLC Number:

O641
O631

TrendMD:

PAN Deng,SUN Zhaoyan. Spatial Density Correlation in Polymer Melts^†[J]. Chem. J. Chinese Universities, 2018, 39(12): 2693.

Figures/Tables 8

Fig.1 Schematic picture of polymers with different chain architectureGreen beads represent the branched points. The total number of beads in each chain is 22. There are 7 beads in each arm of the star polymer(3-Arm star). The H-shaped polymer(H-shape) consists of five identical linear polymer chains with lengths 4 and 2 branched beads.

Fig.2 Coherent intermediate scattering functions at q*=7.15 for different T of the star polymer(A) and the α relaxation time of different polymer architectures(the solid lines are the VFT fitting curves)(B)

Table 1 VFT fitting parameters

Architecture	D	T₀
Ring	4.64	0.301
Linear	4.50	0.309
3-Arm star	4.53	0.310
H-shape	4.42	0.314

Fig.3 Mean squared displacement of all beads, chain ends and branched beads of H-shaped polymer melts at T=0.48

Fig.4 Distribution of Voronoi cell volumes of branched beads, all beads and chain ends of H-shaped polymer melts at T=0.48

Fig.5 Temperature dependence of the mean Voronoi cell volumes of chain ends(A), ordinary beads(B) and branched beads(C)

Fig.6 Distribution of Voronoi cell volumes of star polymer at different temperature(A) and rescaled distribution of Voronoi cell volumes of all beads, chain ends and branched beads at all state points(B)

Fig.7 Temperature dependence of the number averaged cluster size which consists of beads with large Voronoi cell volume, i. e., loosely packed particles(A) and beads with small Voronoi cell volume, i. e., densely packed particles(B)a. Ring; b. linear; c. 3-Arm star; d. H-shape.

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