模拟研究聚合物在受限环境中的自组装结构和动力学性质

发布时间：2018-11-19 10:15

【摘要】：聚合物在受限环境中的自组装结构及动力学行为是软物质领域的两个重要研究方向。由于施限体对聚合物的空间限制及相互作用,使得聚合物表现出与本体完全不同的行为,因此人们可以通过对聚合物施限获得本体无法得到的纳米结构。聚合物在受限环境中的实验研究较为困难,且难以分析实验过程中的一些动力学变化。计算机模拟能够有效地为实验研究提供一定的理论指导。本文采用计算机模拟方法研究受限环境中的聚合物,研究内容主要包括以下两部分:(1)采用耗散粒子动力学方法模拟研究rod-coil两嵌段共聚物在纳米管中的自组装结构。考察了纳米管的性质、管径、刚性嵌段的刚性度及刚性嵌段长度等因素对自组装结构的影响,获得了R6C6两嵌段共聚物的组装结构随管壁性质和管径变化的相图。在非选择性和弱选择性纳米管中,我们观察到堆叠层、单螺旋和双螺旋。在强选择性纳米管中,随着管径的增加,柔性嵌段在纳米管内部组装成堆叠层、柱、zigzag(ZZ)、并进一步演化成锁链、波纹管和螺旋管等多种新颖的有序结构。我们发现ZZ结构是后续结构的组装单元,为此我们分析了ZZ结构的动力学形成过程,发现柔性嵌段形成的ZZ结构主要是由于强选择性壁面的吸引,使得刚性嵌段向壁面移动,并在壁面附近聚集组装。最后,我们获得了组装结构随链长和管径变化的相图,我们的模拟结果表明刚性嵌段的刚性度、管壁对嵌段的选择性、及管径与本体周期的不匹配的协同作用导致各种自组装结构的形成。(2)采用粗粒化分子动力学方法模拟研究均聚物在平面狭缝中的构象及动力学性质。主要考察了均聚物的链长、浓度和狭缝厚度的影响,分析了聚合物在溶液中和狭缝中的差异。随着狭缝厚度的降低,聚合物链经历了从本体的柔性线团,先压缩后拉伸的变化趋势,聚合物链的均方回转半径先下降后升高。聚合物的浓度越小,拉伸趋势越明显。相反,聚合物的浓度越大,压缩趋势越明显。通过计算链的自扩散系数DXY和弛豫时间?,我们发现链长N80的均聚物链为非缠结链,符合Rouse动力学模型,当链长N80时,均聚物可视为为缠结链,属于Reptation动力学模型。对于非缠结链,当浓度较小时,随着链长和浓度的增加,以及狭缝厚度的降低,DXY先下降后上升,τ增加,表明空间限制促进聚合物链沿水平方向的运动。当浓度较大时,DXY单调下降,τ增加,表现为空间限制及链相互作用对聚合物运动的抑制。对于缠结链,低浓度下与非缠结链表现一致;高浓度时,随着链长和浓度的增加,以及狭缝厚度的降低,DXY经历了先上升后下降,τ经历了先下降后上升的变化,主要表现为空间限制效应与链缠结作用的相互竞争。
[Abstract]:Self-assembly structure and kinetic behavior of polymers in confined environment are two important research directions in soft matter field. Due to the space limitation and interaction of the polymer, the polymer behaves completely different from the bulk, so the nanostructure which can not be obtained by the polymer can be obtained by limiting the polymer. The experimental study of polymer in confined environment is difficult, and it is difficult to analyze some dynamic changes in the experimental process. Computer simulation can effectively provide theoretical guidance for experimental research. In this paper, the polymer in confined environment is studied by computer simulation. The main contents are as follows: (1) the self-assembly structure of rod-coil diblock copolymers in nanotubes is simulated by dissipative particle dynamics method. The effects of the properties of nanotubes, the diameter of the nanotubes, the rigidity of rigid blocks and the length of rigid blocks on the self-assembly structure were investigated. The phase diagrams of the R6C6 diblock copolymers with the variation of the wall properties and the pipe diameters were obtained. In non-selective and weakly selective nanotubes, we observed stacked layers, single helix and double helix. In the highly selective nanotubes, with the increase of the diameter of the nanotubes, the flexible blocks are assembled into stacked layers within the nanotubes, and the column, zigzag (ZZ), further evolves into a variety of novel ordered structures such as chains, corrugated tubes and spiral tubes. We find that the ZZ structure is the assembly unit of the subsequent structure. For this reason, we analyze the dynamic forming process of the ZZ structure. We find that the flexible block formed by the ZZ structure is mainly due to the attraction of the strongly selective wall, which makes the rigid block move toward the wall. And assembled near the wall. Finally, we obtain the phase diagram of the assembly structure with the length of the chain and the diameter of the pipe. Our simulation results show that the rigidity of the rigid block, the selectivity of the pipe wall to the block, The synergetic effect of the mismatch between the diameter of the tube and the period of the body leads to the formation of various self-assembled structures. (2) the conformation and kinetic properties of homopolymer in plane slit are studied by means of coarse-grained molecular dynamics method. The effects of chain length, concentration and slit thickness of homopolymer were investigated, and the difference of polymer in solution and slit was analyzed. With the decrease of slit thickness, the polymer chain experienced the change trend of the flexible coils from the body, first compressed and then stretched, and the mean square radius of rotation of the polymer chain first decreased and then increased. The lower the concentration of polymer, the more obvious the tensile trend. On the contrary, the higher the polymer concentration, the more obvious the compression trend. By calculating the chain self-diffusion coefficient (DXY) and relaxation time, we find that the homopolymer chain with chain length N80 is a non-entangled chain, which accords with the Rouse kinetic model. When the chain length is N80, the homopolymer can be regarded as a entangled chain, which belongs to the Reptation kinetic model. For non-entangled chains, with the increase of chain length and concentration, and the decrease of slit thickness, DXY decreases first and then increases, 蟿 increases when the concentration is small, which indicates that space restriction can promote the movement of polymer chains along the horizontal direction. When the concentration is high, DXY decreases monotonously and 蟿 increases, which shows that the restriction of space and the inhibition of chain interaction on the movement of polymer. For entangled chain, it is consistent with non-entangled chain at low concentration. At high concentration, with the increase of chain length and concentration, and the decrease of slit thickness, the DXY goes up first and then decreases, 蟿 goes through the change of decreasing first and then rising, which mainly shows the competition between spatial restriction effect and chain entanglement.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O631.1

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