【作者】 钱虎军；

【导师】 孙家钟； 吕中元；

【作者基本信息】 吉林大学 ， 物理化学， 2007， 博士

【摘要】 本论文利用耗散粒子动力学模拟方法,分别对环形二嵌段共聚物、具有不同链柔性的多手臂型嵌段共聚物体系的微观相行为,不相容A/B型均聚物及其嵌段共聚物共混界面,以及表面吸附高分子扩散动力学标度进行了研究。主要内容包括:利用耗散粒子动力学模拟方法,研究了环形二嵌段共聚物在本体中的微观相分离行为,构筑了其相分离的相图,并且将结果与线形共聚物的相图进行对比,揭示了环形链拓扑结构对其相行为的影响。对于不相容A/B型均聚物及其嵌段共聚物共混界面,全面细致地研究了链长、相互作用强度、嵌段共聚物浓度分布等因素对体系界面热力学性质(界面厚度和界面张力)的影响。并且将结果和蒙特卡罗和自洽场的结果进行了对比。研究了分子链柔性以及链拓扑结构对多手臂(miktoarm)型嵌段共聚物体系分别在三维和二维空间中微观相分离行为的影响。通过在DPD方法中构筑合理的固体表面,研究了吸附在不同类型表面上的高分子单链在稀溶液环境下的扩散动力学行为及其标度规律。揭示了高分子链在生物膜表面和固体表面产生不同扩散动力学行为的原因所在。更多还原

【Abstract】 As a fertile source of soft materials, block copolymer have novel properties resulted form their ability of self-organizing into various ordered structures in melts or solutions. The morphology of the block copolymer can be influenced by many factors, including internal factors (such as chain length, molecular fraction, and interactions between different components etc.) and external ones (such as temperature, conditions of processing etc.). For the polymer blends, how to improve its properties by strengthening the polymer/polymer interfaces is nevertheless one of the most important targets of polymeric material sciences. Exploring the diffusion dynamics and the scaling law of polymer chain adsorbed on a surface is very important for studying the self-organizing phenomena of polymers on surfaces and other related surface phenomena. All about these are always the focus in scientific research or application fields.Computer simulations can visualize these physical processes directly. It helps us understand and explore the laws in these natural phenomena. In this dissertation, we carry out comprehensive dissipative particle dynamics simulations (DPD) to study the topics we mentioned above. Within the DPD method, all the particles interact with each other through three pairwise forces: a conservative force, a dissipative force, and a random force. These forces are very soft, so the integration time steps can be very large, the time scale in DPD simulation can be at milliseconds. It’s also due to the soft repulsions, we can unite some molecules or polymer segments into one DPD bead, thus the DPD model can be used to study the systems at mesoscopic length scale.Hydrodynamic interactions (HI) is very important for microphase separation of the block copolymers and it is intrinsically embedded in the DPD model because of the pari-wise interactions which result the momentum of the system being conserved. DPD method has been applied on the study of polymer blends, microphase separation of the block copolymers, self-organizing of amphiphilic molecules into memberane, and the budding and fission of bionic micells. In our study, DPD method is used to study the microphase separations of cyclic diblock copolymers, and that of miktoarm block copolymers with different chain rigidity and molecular shape. Incompatible interfaces in polymer blends and surface diffusion dynamics of single polymer chain are also studied comprehensively by carrying out DPD simulations. The main results are as follows:(1) For the cyclic diblock copolymer system, The dissipative particle dynamics (DPD) simulation method is applied to study the mesoscopic phase formation of cyclic diblock copolymer c-AmBn (m + n=20). The phase diagram is constructed by simulating at different interaction parameters and composition fractions. The resulted phase diagram is similar to that of the linear diblock copolymer; i.e., the ordered structures such as lamellae, perforated lamellae, hexagonal cylinders, and body-centered-cubic spheres can be identified in the parameter space. Melted structures such as micelle-like, liquid rod, and random network phases have also been found in the phase diagram. The observed 40<(χN)ODT≤45 is in agreement with the theoretical prediction, (χN)ODT=43.8 for finite chain length, if a finite chain length mapping is applied. Cyclization of a linear block copolymer can induce remarkable changes in the morphology of the organized meso-structure. This is attributed to the reduced chain length of the cyclic block copolymer. The existence of the melted structures between totally disordered and the ordered phases emphasizes complex dynamical pathway during microphase separations.(2) For the incompatible A/B homopolymer blends and with their block copolymers, dissipative particle dynamics simulations are carried out to investigate the thermodynamic interfacial properties. For the binary blends, the interfacial tension increases and the interface thickness decreases with increasing Flory–Huggins interaction parameterχwhile the homopolymer chain length is fixed. However, when theχparameter and one of the homopolymer chain length is fixed, increasing another homopolymer chain length will induce only a small increase on interfacial tension and slight decrease on interface thickness. For the ternary blends, adding the AB block copolymer will reduce the interfacial tension. When the mole number of the block copolymer is fixed, longer block chains have higher efficiency on reducing the interfacial tension than the shorter ones. But for the block copolymers with fixed volume fraction, shorter chains will be more efficient than the longer ones on reducing the interfacial tension. Increasing the block copolymer concentration reduces interfacial tension. This effect is more prominent for shorter block copolymer chains.(3) For the miktoarm block copolymer system, we study influence of the chain rigidity and the topology shape of the molecule on the behavior of microphase separation in 3 dimensional (3D) and 2 dimensional (2D) systems. (i) In 3D, we have studied the influence of the molecule rigidity on the nanostructures of the A2(B4)2-type miktoarm block copolymers. A typical spherical micellar ordered structure is obtained for a coil-coil miktoarm block copolymer in melt. By introducing a bond angle potential in our model to enhance the molecule rigidity systematically, we find, respectively, a hexagonal cylindrical structure and a parallel ellipsoid in lamellae (PERL) structure which is discovered for the first time. (ii) In 2D system, The microphase separation of miktoarm block copolymers with different compositions and chain rigidities is studied using dissipative particle dynamics. The pure coil, rod-coil, and pure-rod models are considered, and complex micelles, tubular micelles, lamellae and networks morphologies are obtained for these systems. The influence of the molecule flexibility and shape on the morphology is emphasized for the special“Y”- and“T”-shaped miktoarm block copolymers. From an application point of view, these results will be helpful for designing new templates of block copolymers in thin films for the fabrication of nanostructures.(4) Comprehensive three dimensional dissipative particle dynamics simulations are carried out for the first time to elucidate the diffusion mechanism of strongly adsorbed polymer chain on solid surface in dilute solutions. We find Rouse and reptation dynamics for polymer chain diffusing on smooth and disordered surfaces (with obstacles and sticking points), respectively. The interactions between the surface and the fluid screen the hydrodynamic interaction. The different scaling as found for polymer chain diffusing on fluid membrane [Phys. Rev. Lett. 82, 1911 (1999)] and on solid surface [Nature 406, 146 (2000)] may be explained by the solid surface inhomogeneity that induces reptation.更多还原