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Molecular dynamics simulations of oligoester brushes: the origin of unusual conformations
Soft Matter ( IF 3.4 ) Pub Date : 2017-09-11 00:00:00 , DOI: 10.1039/c7sm01419h
A. D. Glova 1, 2, 3, 4 , S. V. Larin 1, 2, 3, 4 , S. G. Falkovich 1, 2, 3, 4 , V. M. Nazarychev 1, 2, 3, 4 , D. A. Tolmachev 1, 2, 3, 4 , N. V. Lukasheva 1, 2, 3, 4 , S. V. Lyulin 1, 2, 3, 4
Affiliation  

We present results from all-atom molecular dynamics simulations for the structural properties of oligomeric lactic acid chains (OLA) grafted to the surface of cellulose nanocrystals (CNCs) and immersed in the melt of polylactic acid (PLA). Earlier, we have found that the distribution of free ends of OLA molecules is bimodal [Glova et al., Polym. Int., 2016, 65(8), 892]. The results cannot be explained within the standard picture of uncharged polymer brushes exposed to the melt of a chemically identical polymer. Although the oligomeric brushes of the OLA chains are uncharged, they have partial polarization charges producing a non-zero dipole moment of the monomeric chain unit. We study the influence of partial charges on the structure of the layer of OLA chains grafted to the CNC surface. A detailed analysis of the conformations of the grafted chains shows that interaction of partial charges in the models causes bending of the OLA molecules toward the cellulose surface, forming a hairpin structure. The observed separation of the grafted chains into two populations increases with grafting density. We demonstrate that hydrogen bonds can be formed between the free ends of the grafted chains and the CNC surface, but they do not affect the brush structure significantly. Thus, dipole–dipole interactions turn out to be the key factor governing the unusual conformations of grafts.

中文翻译:

低聚酯刷的分子动力学模拟:异常构象的起源

我们目前从全原子分子动力学模拟的结果,接枝到纤维素纳米晶体(CNCs)的表面并浸没在聚乳酸(PLA)熔体中的低聚乳酸链(OLA)的结构特性。早些时候,我们发现OLA分子的自由端分布是双峰的[Glova等。Polym。诠释 2016,65(8),892]。结果无法在未充电的聚合物电刷暴露于化学相同的聚合物熔体的标准图片中进行解释。尽管OLA链的低聚刷子不带电,但它们具有部分极化电荷,会产生单体链单元的非零偶极矩。我们研究了部分电荷对接枝到CNC表面的OLA链层结构的影响。对接枝链构象的详细分析表明,模型中部分电荷的相互作用导致OLA分子向纤维素表面弯曲,形成发夹结构。观察到的将接枝链分为两个种群的分离随着接枝密度的增加而增加。我们证明可以在接枝链的自由端和CNC表面之间形成氢键,但它们不会显着影响电刷的结构。因此,偶极-偶极相互作用最终成为支配移植物异常构象的关键因素。
更新日期:2017-09-20
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