聚合物结晶与导热性能的分子模拟研究

发布时间：2018-05-01 07:12

本文选题：分子模拟 + 聚乙烯　；参考：《安徽大学》2017年硕士论文

【摘要】：高分子材料在电子、工程、机械等领域具有广泛的应用价值。然而,高分子材料较差的导热性能,限制了其在热管理材料领域的应用。高分子本体的导热率只有0.1-1 W/mK,远远低于陶瓷和金属材料。通过加入导热填料可以有效提高复合体系的导热性能,然而填充型高分子复合材料的有机-无机界面严重影响材料的机械力学性能。随着电子信息和新材料产业的发展,如何综合提高高分子材料的导热和机械力学性能成为高分子研究领域的重点。高分子的物理性能与其微观形态结构关系密切。高分子体系中晶体的尺寸和取向、导热填料与基体的复合状态、填料颗粒之间的物理/化学键合等因素对材料的性能有重要的影响。本文采用计算机模拟方法研究了聚合物结晶、导热性能和聚合物交联纳米颗粒的影响因素和体系微观结构和状态的演变规律。首先,采用分子动力学的方法模拟了聚乙烯体系和聚乙烯/氮化硼复合体系导热率随拉伸作用的变化。采用非平衡分子动力学(nonequilibrium molecular dynamics,NEMD)方法测定了聚合物体系导热率与拉伸形变、拉伸速率、温度、分子摩尔质量的关系。结果表明:对于纯聚乙烯体系,拉伸作用通过改变分子的取向结构来达到提升导热率的效果。随着拉伸作用的进行,分子由无序混乱的状态达到沿拉伸方向高度有序的晶体结构,使得热量在传递过程中沿分子链传递大于分子间传递,大大提高了导热效率。拉伸速率、温度、聚乙烯分子的分子质量都会影响取向结构,达到相同的形变条件时拉伸速率越小分子的取向率越高;温度也影响着拉伸取向的速率,对应不同的拉伸速率,温度的效果不一样;分子的大小同样影响聚合物的导热速率,在相同的取向条件下,分子摩尔质量越大聚合物的导热系数越高。对于聚乙烯氮化硼复合体系,氮化硼片层由于自身的性质使其诱导聚乙烯分子形成了有序结构同样提升了聚合物的导热率。纳米添加剂的作用不仅仅是利用自身高导热的性质在聚合物体系中形成导热通路来提高材料导热率,其与聚合物材料间的相互作用改变聚合物的结构也是提升材料导热性能的一个重要影响因素。然后研究了两种不同构型氮化硼纳米材料对于聚合物结晶的影响。熔体条件下,通过对聚乙烯分子结晶过程中晶体构象的演变、空间内分子分布的变化以及分子扩散特性的研究,结果表明氮化硼纳米管诱导PE烷烃分子结晶的速率明显要比氮化硼片层的快。纳米材料由于自身维度的不同,诱导结晶的能力也不同,氮化硼纳米结构的曲率半径会影响聚合物在其表面结晶的速率。构象演变过程和键取向参数的变化表明,使氮化硼片层诱导结晶能力低于氮化硼纳米管的原因是PE分子在氮化硼表面的多重的取向,而PE分子在氮化硼纳米管表面的取向均是沿着纳米管轴向方向,说明纳米材料维度是影响聚合物结晶的重要影响因素。最后采用DPD方法讨论一种纳米填料纳米链合成的影响因素,通过对表面接枝纳米颗粒在溶液中的成键反应,系统地研究了反应的影响因素。考虑了接枝链的长度(从30到90)和接枝密度从低到高(0.04至0.16)和接枝链的刚性。确定了纳米颗粒间成键率与接枝链长度、接枝密度、接枝链刚度、浓度的关系。结果证明,控制纳米粒子的接枝链的长度是最有效的方法,接枝链的长度存在一个最优值,在不同的接枝密度下,当接枝链长度低于最优质时提高接枝链链长度有利于纳米颗粒间成键链接,当接枝链长度高于最优值时提升接枝链长度有相反作用。此外,改变接枝链的密度,接枝链的刚度也被认为是一个重要因素。对于不同接枝密度的纳米粒子,随着接枝密度的增加,颗粒的结合速率变高。浓度对键形成的作用与接枝密度相近,当增加纳米粒子的浓度时,纳米粒子链更容易得到。
[Abstract]:Polymer materials have wide application value in the fields of electronics, engineering and machinery. However, the poor thermal conductivity of polymer materials restricts its application in the field of thermal management materials. The thermal conductivity of the polymer is only 0.1-1 W/mK, far below the ceramic and metal materials. The composite system can be effectively improved by adding heat conductive filler. The organic inorganic interface of filled polymer composites seriously affects the mechanical and mechanical properties of the materials. With the development of electronic information and new materials industry, how to improve the thermal conductivity and mechanical properties of polymer materials has become the key point in the field of polymer research. The crystal size and orientation of the polymer system, the composite state of the thermal conductive filler and the matrix, the physical / chemical bonding between the packed particles have an important influence on the properties of the materials. In this paper, the effects of polymer crystallization, heat conductivity and polymer crosslinked nanoparticles are studied by computer simulation. Firstly, the thermal conductivity of polyethylene system and polyethylene / boron nitride composite system was simulated with the change of tensile effect by molecular dynamics. The thermal conductivity and tension of the polymer system were measured by nonequilibrium molecular dynamics (NEMD) method. The relationship between deformation, tensile rate, temperature and molecular mole quality. The results show that for pure polyethylene system, the tensile effect is achieved by changing the molecular orientation structure to improve the thermal conductivity. As the tensile force is carried out, the molecules are in a disorder and chaotic state to achieve a highly ordered crystal structure along the extension direction, making the heat transfer. The transfer of the molecular chain along the molecular chain is greater than the intermolecular transmission, which greatly improves the thermal conductivity. The tensile rate, the temperature, the molecular mass of the polyethylene molecule all affect the orientation structure. When the same deformation condition is reached, the smaller the tensile rate is, the higher the orientation rate of the molecule; the temperature also affects the rate of tensile orientation, corresponding to the different tensile rate and temperature. The effect of the degree is different, the size of the molecule also affects the heat conduction rate of the polymer. Under the same orientation, the higher the molecular mole mass is, the higher the thermal conductivity of the polymer. For the polyethylene nitride composite system, the boron nitride lamellar formed the ordered structure of the polyethylene molecule by its own properties and promoted the polymerization. The thermal conductivity of the material. The effect of nano additive is not only to improve the thermal conductivity of the material in the polymer system, but also to improve the thermal conductivity of the material in the polymer system. The interaction between the polymer and the polymer material changes the structure of the polymer as well as a key factor to improve the thermal conductivity of the material. Then two kinds of isomorphism are studied. The effect of boron nitride nanomaterials on the crystallization of polymer. Under the melt condition, the evolution of the crystal conformation in the crystallization of polyethylene, the change in the molecular distribution in the space and the molecular diffusion characteristics are studied. The results show that the rate of PE alkanes induced by boron nitride nanotubes is faster than that of the boron nitride layer. The ability of rice materials to induce crystallization is different because of their own dimensions. The radius of curvature of boron nitride nanostructures will affect the rate of polymer crystallization on its surface. The change of conformation evolution and bond orientation parameters indicates that the reason for the crystallization ability of boron nitride layer to induce the crystallization ability is lower than that of boron nitride nanotube, which is the PE molecule in the boron nitride sheet. The orientation of the surface of PE molecules on the surface of BN nanotubes is along the axial direction of the nanotube, indicating that the dimension of nanomaterial is an important factor affecting the crystallization of the polymer. Finally, the influence factors of the nanoscale synthesis of a nano filler are discussed by the DPD method, and the surface grafting of nano particles in the solution is discussed. The influence factors of the bond reaction are systematically studied. The length of the graft chain (from 30 to 90) and the grafting density from low to high (0.04 to 0.16) and the rigidity of the graft chain are taken into account. The relationship between the bond rate of the nanoparticles and the length of the graft chain, the grafting density, the graft chain stiffness and concentration is determined. The results show that the grafting chain of the nanoparticles is controlled. Length is the most effective method. The length of graft chain has an optimal value. Under the different grafting density, the length of the chain chain chain is beneficial to the bond linkage between the nanoparticles when the length of the grafting chain is lower than the best quality. The stiffness of the grafted chain is also considered as an important factor. With the increase of the grafting density, the binding rate of particles becomes higher with the increase of the grafting density. The effect of concentration on the bond formation is similar to that of the grafting density. When the concentration of nanoparticles is increased, the nanoparticle chain is easier to get.

【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O631

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