【作者】 李延春；

【导师】 黄旭日； 吕中元；

【作者基本信息】 吉林大学 ， 物理化学， 2011， 博士

【摘要】 嵌段共聚物自组装是指在没有外界因素的干扰下,线型、接枝、梳型、星型等嵌段共聚物在本体或者溶液中形成有序/功能结构的过程。嵌段共聚物自组装既可以形成薄膜、聚合物刷、多层膜、杂化膜、交联膜和生物膜,又可以形成胶体、胶束、纳米微胶、胶囊、囊泡、核—壳、核—支化壳、乳液和聚集态的纳米粒子等等。比如在本体中,嵌段共聚物通过相分离可以在表面形成有序的薄膜；在溶液中,嵌段共聚物通过亲水/疏水相互作用自组装形成胶束,进而可以得到均聚物吸附在胶束表面的复合体系。嵌段共聚物自组装材料无论是在平面显示、平板印刷、光电材料和高密度数据存储等功能材料领域,还是在药物运输、组织工程学和生物传感器等方面都有潜在的应用,并得到不断发展。然而,嵌段共聚物自组装体系大多属于软物质,因此对外界的微小的刺激都可能产生巨大的响应。在外场的扰动下,刺激响应高分子材料的扩散、吸附和润湿能力都会发生改变,同时将化学和生物信号转化为力学、光学、电学和磁学信号。比如只改变溶剂的选择性,就会对薄膜的形貌产生巨大的影响；微小的剪切扰动,就可以改变均聚物在胶束表面的吸附行为以及胶束本身的结构。到目前为止,自组装的本质和驱动力问题,特别是在非平衡态条件下(电场、磁场、流场等)嵌段共聚物自组装体系的刺激响应机制,一直没有得到根本的解决。随着刺激响应和功能高分子的巨大需求以及嵌段共聚物自组装的复杂性,单纯的实验手段略显捉衿见肘,迫切需要理论和模拟为实验提供数据上的补充。从二十世纪五十年代计算机诞生开始,计算机模拟方法就得到了长足发展,精确的量子化学方法成功地解决了小分子的结构、反应机理以及光电磁等性质。而在高分子领域,也建立了许多成功的模拟方法,主要包括分子动力学,蒙特卡罗,布朗动力学,耗散粒子动力学,格子玻尔兹曼方法,自治场理论,动态密度泛函理论等等。从嵌段共聚物出发,选择适当的方法建立模型,通过计算机程序可以模拟自组装真实的动态过程,进而检验和弥补相关理论和实验上的不足。采用有效的耗散粒子动力学(Dissipative Particle Dynamics,DPD)及其衍生方法,对我们所关心的嵌段共聚物自组装问题进行深入研究,能够很好地解决实验和理论所无法预测和解释的结果。耗散粒子动力学方法中,粒子之间受到的对相互作用力包括保守力、耗散力、随机力三个基本部分。随着研究的深入,弹簧力、键角势等也被加入到耗散粒子动力学方法中,分别用来控制平衡键长和高分子链的柔性。另外,耗散粒子动力学方法可以选用比传统的分子动力学方法大很多的积分步长,采用非常软的相互作用势,模拟的时间尺度可以达到微秒级,空间尺度可以达到微米级。本文利用非平衡态耗散粒子动力学(Non-Equilibrium Dissipative Particle Dynamics,NEDPD)和多体耗散粒子动力学(Multibody Dissipative Particle Dynamics,Multibody DPD)模拟方法,分别研究了吸附在胶束表面上的均聚物链在剪切场下的热力学和动力学行为；在不同的蒸汽诱导、不同的表面诱导、不同的组成以及不同的链的柔性条件下,线型两嵌段、线型三嵌段以及梳型两嵌段、梳型三嵌段共聚物自组装形成的薄膜的结构和性质。主要内容包括：(1)利用平衡态耗散粒子动力学方法,研究了嵌段共聚物自组装形成胶束以及均聚物链在其表面的吸附。进一步采用非平衡态耗散粒子动力学方法,通过加入剪切,研究了均聚物的脱落和胶束的分裂过程。模拟结果揭示了脱落时间随剪切速率的变化规律。(2)利用多体耗散粒子动力学方法研究了对称和非对称条件下,蒸汽诱导线型两嵌段、线型三嵌段共聚物在表面自组装形成薄膜的过程,分别考虑了嵌段共聚物的类型、溶剂和表面以及嵌段共聚物的组成和链的柔性对薄膜结构和性质的影响。我们模拟得到了平行表面的双层、多层薄膜,垂直表面的层状薄膜,球状薄膜和无序状薄膜,并计算了这些薄膜的序参量和薄膜厚度随时间的演化。结果表明,嵌段共聚物的类型和组成、溶剂和表面以及嵌段共聚物链的柔性共同决定了薄膜的形貌和有序程度。蒸汽使薄膜厚度增加并影响靠近界面的薄膜的结构,而表面吸附使薄膜厚度降低并影响靠近表面的薄膜的结构。蒸汽和表面通过对界面和表面的薄膜结构的影响,进而诱导了有序薄膜的形成。当蒸汽和表面一定时,嵌段共聚物的组成对薄膜厚度几乎没有影响,但是对薄膜的有序度有很大影响。当某种组分的链段很短的时候,只能形成序参量较小的无序薄膜,相反则可以得到序参量较大的层状薄膜。嵌段共聚物的组成和链的柔性也可以对薄膜的形貌进行调控。(3)利用多体耗散粒子动力学方法研究了蒸汽诱导梳型两嵌段、梳型三嵌段共聚物在表面自组装形成薄膜的过程,分别考虑了嵌段共聚物的类型、溶剂和表面对薄膜结构和性质的影响。我们模拟得到了平行表面的层状相中夹杂着垂直表面层状相的有序薄膜,球状薄膜和无序状薄膜,并计算了这些薄膜的厚度随时间的演化。结果表明,嵌段共聚物的类型、溶剂和表面共同决定了薄膜的形貌和有序程度。薄膜的厚度同样由蒸汽和表面决定,吸引的表面使薄膜厚度降低,而蒸汽使薄膜厚度增加。蒸汽和表面通过对界面和表面的薄膜结构的影响,进而诱导了有序薄膜的形成。然而,梳型嵌段共聚物与线型嵌段共聚物相比,不容易形成平行或垂直表面的薄膜,更容易形成层状中夹杂着层状的有序薄膜。总之,我们的研究结果将为基因治疗、复杂组装体和介孔材料的结构调控提供可靠的理论帮助。更多还原

【Abstract】 Self-assembly of block copolymers is the process in which linear, graft, comb, and star block copolymers organize into ordered and/or functional structures without human intervention. These structures include thin films, polymer brushes, multilayered films, hybrid systems that combine polymers and particles, thin films of polymer networks, and membranes with channels/pores and nanoparticles (colloids, micelles, nanogels, capsules and vesicles, core-shell particles, hybrid particle-in-particle structures). In melt, the block copolymers via self-assembly can form ordered thin films on substrate. In solution, block copolymers via hydrophobic and hydrophilic interaction to form micelle and composite systems that homopolymer chains are adsorbed on the surface. These materials are possess potential applications and rapid developments in lots of aspects, such as photoelectricity apparatus, panel displays, lithography, high density data storage, as well as drug delivery, tissue engineering and biosensors. These materials are also related to soft matter so that a strong responsive signal can be induced by small stimuli. Stimuli-responsive polmer materials can change diffusion, wettability and adhesion of components on external field, as well as transform chemical and biochemical signals into mechanical, thermal, electrical and optical signals and so on. For example, the morphologies of block copolymer thin films are largely dependent on selective solvents, the homopolymer desorption and micelle fission induced by a weak shear. So far, the nature and driving force of self-assembly, especially in the non-equilibrium conditions (electric field, magnetic field, flow field), the stimuli-responsive mechanism of block copolymers self-assembly have not been fundamentally resolved.With the rapid development of stimuli-responsive and functional polmer materials, combining theoretical and simulation with experiment to study the self-assembly of block copolymers, becomes increasingly important in scientific area. With the invention of computer in the twentieth century fifties, the computer simulation method has made considerable progress. The precise quantum chemical method successfully resolves the structures of small molecules, reaction mechanisms, and optical, electromagnetic, magnetic properties. In the polymer field, there are also a number of successful simulation methods, including molecular dynamics, Monte Carlo, Brownian dynamics, dissipative particle dynamics, lattice Boltzmann method, self-consistent field theory, the dynamic density functional functional theory and so on. For the block copolymers, a. computer program can simulate the real dynamic process of self-assembly, and then test the theory and experiment, and make up the deficiencies. Using the effective dissipative particle dynamics and its derivative methods, we are able to study the block copolymers self-assembly in-depth. It is a good method to predict and interpret the results that experiment and theory can not obtain. In dissipative particle dynamics method, all the interactions among particles by three basic pairwise forces, including conservative force, dissipative force and random force. The spring force and the bond angle potential are also added to the DPD method, which used to control the equilibrium bond length and the flexibility of the polymer chain. These forces are softer and the integration time step is larger, so the time scale in DPD simulation can be at milliseconds, while the length scale can be at microns.In this paper, non-equilibrium dissipative particle dynamics and multi-body dissipative particle dynamics simulation methods are used to study on the thermodynamic and kinetic behavior of micelle formation and the adsorbed homopolymer under shear field, the structures and properties of thin films self-assembly by the linear diblock, linear triblock, and comb-type diblock, comb-type triblock copolymers with different evaporation, different surface, different components and different chain flexibilities, respectively. The main results are as follows:(1) We use equilibrium dissipative particle dynamics method to investigate the micelle formed by self-assembly of block copolymers, where a homopolymer chain is adsorbed on the micelle surface. Under shear flow, we use non-equilibrium dissipative particle dynamics method to investigate the processes of the homopolymer desorption and micelle fission. The results reveal the dependence of desorption time on the shear rate.(2) We use multibody dissipative particle dynamics method to investigate the thin film formed by self-assembly of linear diblock and linear triblock copolymers on attractive surface induced by evaporation, both in symmetric and asymmetric conditions. We consider the type and composition of block copolymers, the solvent effect, the surface effect and the flexibility of chains on the morphologise of linaer diblock and linean triblock copolymer thin films. We obtain two-layer and multi- layer lamellar morphology parallel to the surface, lamellar morphology perpendicular to the surface, spherical morphology and disorder morphology, and study the time evolution of the order parameter and the film thickness. The results show that the type and composition of block copolymers, the evaporation, the surface, and the flexibility of the chains determine the film morphology, the film thickness and the degree of ordering. The attractive solvent vapor increases the film thickness and impacts the film morphology at the interface. The attractive surface decreases the film thickness and impacts the film morphology near the surface. Solvent vapor and the surface strongly influence the interface and surface structures of the thin films, and then induce the formation of ordered thin films. When the solvent vapor and the surface interactions are constant, the composition of block copolymers has little effect on the film thickness, but has great influence on the degree of order. If one of the compositions is shorter, it is easy to form disordered morphology with small order parameter. On the other hand, if the two compositions are nearly equal, it is easy to form lamellar morphology with big order parameter. The chain’s flexibility has a great influence on thin film morphology, too.(3) We use multibody dissipative particle dynamics method to investigate the thin film formed by self-assembly of comb-type diblock and comb-type triblock copolymers on surface induced by evaporation condition. We consider the type of block copolymers, the solvent effect, and the surface effect on the morphology of comb-type diblock and comb-type triblock copolymer thin films. We obtain order in order lamellar morphology, sandwich morphology, spherical morphology and disorder morphology, and study the time evolution of the order parameter and the film thickness. The results show that the type of block copolymers, the evaporation, and the surface determine the film morphology and the degree of order. The film thickness is also determined by solvent vapor and surface, where the attractive increases the film thickness and the attractive surface decreases the film thickness. Solvent vapor and the surface induce the interface and surface structure of the thin film, and then induce the formation of ordered thin films. However, the comb-type copolymers, compared with the linear block copolymers are not easy to form lamellar morphology parallel or perpendicular to the surface, more likely to form order in order lamellar morphology.In summary, our results may be helpful for the gene therapy, regulation of complex assembly, and the structure control of the mesoporous materials.更多还原