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Molecular dynamics simulations have been used to study the effect of the pre-orientation on the microstructure of lamella crystal and the stress response of polyvinyl alcohol (PVA) semicrystalline polymer under stretching. For the different pre-oriented systems, nucleation is demonstrated to be a two-step process, however, in a different intermediate order. For the isotropic PVA polymer melt, the segment needs more time to adjust its inter-chain structure, therefore, the nucleation is assisted by local order structures, while the nucleation of the oriented PVA melt is promoted by density fluctuation. The nucleation process is the result of coupling effect of conformational and orientational ordering. The transformation from flexible chains into conformational ordered segments circumvents the entropic penalty under the shear flow, which is the most peculiar and rate-limited step in polymer crystallization. Therefore, the current work suggests that the acceleration of the nucleation rate by shear deformation is mainly attributed to the different kinetic pathway via conformational/orientational ordering-density fluctuation-nucleation. From the different pre-oriented PVA semicrystalline polymers, we know that the higher oriented degree corresponds to a higher number of Tie chains and lower Loop chains, and the higher number of Tie chains corresponds to a stronger stress-strain response. And the detailed molecular structural evolution of semicrystalline polymer under stretching is also given in this work.
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Keywords:
- pre-oriented /
- crystallization /
- polyvinyl alcohol melts /
- amorphous /
- stress-strain
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图 1 (a)高分子熔体剪切示意图; (b)高分子熔体在剪切场温度为T = 1.0下的σxy, Rete及Pall演化曲线
Figure 1. (a) Schematic diagram of polymer melts under shear flow; (b) evolutions of σxy, Rete and Pall for polymer melts under shear with temperature of T = 1.0.
图 2 (a)成核原子判定方法示意图; (b)伸直链判定方法示意图; (c) PVA半晶态高分子结构晶区与无定型区S值的分布
Figure 2. Schematic diagram of (a) centro-symmetry parameter and (b) stretched chain segment for PVA crystal; (c) S distribution of crystal and melt of PVA semicrystalline polymers.
图 3 不同应变下PVA熔体的
${\phi _{\rm{c}}}$ , d tt, V和S随时间的演化过程 (a) γ = 0; (b) γ = 1; (c) γ = 1.5; (d) γ = 2; (e) γ = 4; (f) γ = 8Figure 3. Evolutions of
${\phi _{\rm{c}}}$ , d tt, V and S of nucleation atoms under different stains: (a) γ = 0; (b) γ = 1; (c) γ = 1.5; (d) γ = 2; (e) γ = 4; (f) γ = 8.
图 4 (a)半晶态高分子结构中无定型对应的链结构分类模型; (b), (c) PVA半晶态高分子结构中晶体和无定型的原子结构
Figure 4. (a) Schematic diagram of crystalline and amorphous chain structure for the semicrystalline polymers; (b) and (c) atomic structure of crystal and melt of PVA semicrystalline polymers.
图 5 (a)不同剪切应下PVA半晶态高分子对应的
${\phi _{\rm{c}}}$ 、晶体取向参数Pc和无定型结构取向参数Pa; (b)不同剪切应变下PVA半晶态高分子无定型链结构数目的演化Figure 5. (a)
${\phi _{\rm{c}}}$ , crystalline order parameter Pc, and amorphous order parameter Pa for PVA semicrystalline polymers with different shear strains; (b) the evolution of the numbers of amorphous chains for PVA semicrystalline polymers with different shear strains.
图 6 不同预取向半晶态高分子结构在恒定速率为
$1 \times {10^{{\rm{ - }}5}}{\tau ^{ - 1}}$ 拉伸场下对应的应力-应变曲线Figure 6. Stress-strain curves of PVA semicrystalline polymer with different orientation degree under the stretched rate of
$1 \times {10^{{\rm{ - }}5}}{\tau ^{ - 1}}$ .
图 7 当γ = 6时对应的单链构象随着应变ε的演化过程
Figure 7. Structural evolution of single PVA chain as a function of strain ε when γ = 6.
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[1] Li L, de Jeu W 2005 Adv. Polym. Sci. 181 75
[2] Liu D, Cui K, Huang N, Wang Z, Li L 2015 Sci. China Chem. 58 1570
Google Scholar
[3] Stephanou P S, Tsimouri I C, Mavrantzas V G 2016 Macromolecules 49 3161
Google Scholar
[4] Luo C, Kröger M, Sommer J U 2016 Macromolecules 49 9017
Google Scholar
[5] Luo C, Kröger M, Sommer J U 2017 Polymer 109 71
Google Scholar
[6] Tang X, Yang J, Xu T, Tian F, Xie C, Li L 2017 Phys. Rev. Mate. 1 073401
[7] Yang J, Tang X, Wang Z, Xu T, Tian F, Ji Y, Li L 2017 J. Chem. Phys. 146 014901
Google Scholar
[8] Tang X, Yang J, Tian F, Xu T, Xie C, Chen W, Li L 2018 J. Chem. Phys. 149 224901
Google Scholar
[9] Yamamoto T 2014 Macromolecules 47 3192
Google Scholar
[10] Baig C, Edwards B J 2010 Europhys. Lett. 89 36003
Google Scholar
[11] Yang J S, Yang C, Wang M, Chen B, Ma X 2011 Phys. Chem. Chem. Phys. 13 15476
Google Scholar
[12] Yang J S, Huang D H, Cao Q, Li Q, Wang L, Wang F 2013 Chin. Phys. B 22 098101
Google Scholar
[13] 杨俊升, 黄多辉 2019 68 138301
Google Scholar
Yang J S, Huang D H 2019 Acta Phys. Sin. 68 138301
Google Scholar
[14] 杨文龙, 韩浚生, 王宇, 林家齐, 何国强, 孙洪国 2017 66 227101
Google Scholar
Yang W L, Han J S, Wang Y, Lin J Q, He G Q, Sun H G 2017 Acta Phys. Sin. 66 227101
Google Scholar
[15] 潘登, 刘长鑫, 张泽洋, 高玉金, 郝秀红 2019 68 176801
Google Scholar
Pan D, Liu C X, Zhang Z Y, Gao Y J, Hao X H 2019 Acta Phys. Sin. 68 176801
Google Scholar
[16] Cui K, Ma Z, Wang Z, Ji Y, Liu D, Huang N, Chen L, Zhang W, Li L 2015 Macromolecules 48 5276
Google Scholar
[17] Cui K, Meng L, Ji Y, Li J, Zhu S, Li X, Tian N, Liu D, Li L 2014 Macromolecules 47 677
Google Scholar
[18] Luo C, Sommer J 2016 ACS Macro Lett. 5 30
Google Scholar
[19] Tang X, Chen W, Li L 2019 Macromolecules 52 3575
Google Scholar
[20] Meyer H, Müller-Plathe F 2001 J. Chem. Phys. 115 7807
Google Scholar
[21] Luo C, Sommer J 2009 Comp. Phys. Comm. 180 1382
Google Scholar
[22] Wang S, Wang Y, Cheng S, Li X, Zhu X, Sun H 2013 Macromolecules 46 3147
Google Scholar
[23] Kelchner C L, Plimpton S, Hamilton J 1998 Phys. Rev. B 58 11085
Google Scholar
[24] Wang Z, Ju J, Yang J, Ma Z, Liu D, Cui K, Yang H, Chang J, Huang N, Li L 2016 Sci. Rep. 6 32968
Google Scholar
[25] Wang Y, Jiang Z, Wu Z, Men Y 2013 Macromolecules 45 518
Google Scholar
[26] Siviour C R, Jordan J L 2016 J. Dyn. Behav. Mater. 2 15
Google Scholar
[27] Lin Y, Li X, Meng L, Chen X, Li L 2018 Macromolecules 51 2690
Google Scholar
[28] Lin Y, Li X, Meng L, Chen X, Lü F, Zhang Q, Li L 2018 Polymer 148 79
Google Scholar
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