平板狭缝中两嵌段共聚高分子微观相变的Monte Carlo模拟

采用改进的键长涨落空穴扩散算法对平板狭缝中的对称两嵌段共聚高分子熔体的微相分离形态、密度分布以及结构因子进行了MonteCarlo(MC)模拟 .模拟结果表明 :在不同性质壁面的平板狭缝中对称两嵌段共聚高分子熔体的微相结构都是层状的 ,但其取向由壁面性质决定 ,对称中性壁面形成垂直于壁面的层状结构 ,对称选择性吸引壁面以及非对称的选择性吸引和选择性排斥壁面组合导致平行于壁面的层状结构 ,而非对称的选择性吸引和中性壁面的组合形成的层状结构 ,在吸引壁一侧平行于壁面、在中性壁一侧则垂直于壁面 .对结构因子的计算表明对称体系微相结构主要取决于外场的对称性     

非对称两嵌段高分子在选择性壁面识别吸附的Monte Carlo模拟

采用自由空间的Monte Carlo（MC）方法研究了两嵌段非对称高分子在选择性壁面上的吸附与识别。研究表明;非对称嵌段高分子同对称嵌段高分子一样;在选择性壁面的吸附可分为吸附和识别两个过程。对高分子构型研究的结果发现;无论条纹宽度如何变化;高分子在垂直于z方向的均方回转半径总是小于其垂直另两方向的值。在条纹宽度一定的情况下;尾式构型比率随链节B与白色条纹壁面作用能Ψ ^B-white增加先增加然后趋于不变。在Ψ ^B-white不变的情况下;尾式构型比率则随条纹数的增加而增加。环式构型比率在条纹较宽时会随Ψ ^B-white有一小的下降趋势;而在条纹较窄时下降幅度较大。     

高分子构象模拟研究中的Monte Carlo方法

介绍了Monte Carlo方法及其特点,进而分析了Monte Carlo用于高分子模拟的优势,并描述了两类模拟模型。论文重点综述了近年来Monte Carlo方法在高分子构象模拟中的一些研究与应用,并展望了Monte Carlo方法在高分子构象模拟中的发展趋势和前景。     

共聚高分子吸附的Monte Carlo模拟

用MonteCarlo方法对选择性溶剂中两嵌段共聚高分子在固液界面的吸附进行了模拟 ,获得了吸附等温线以及吸附层厚度、链附着率、表面覆盖率、链节浓度分布等表征吸附层结构的信息 ,同时模拟获得了固液界面区吸附构型大小及分布等表征高分子构型的微观信息 ,考察了吸附性链节A所受的对比排斥能、链组成以及体相浓度等因素对这些参数的影响 .     

高分子抑制蛋白质聚集的动态Monte Carlo模拟

抑制聚集是蛋白质产品下游加工特别是制剂过程中的重要问题。本文采用动态Monte Carlo方法和二维晶格HP蛋白质模型,通过建立高分子-蛋白质复合物微观结构和蛋白质构象概率分布来研究高分子对蛋白质聚集行为的影响。结果表明,高分子的疏水性、分子量及其浓度对于蛋白质的聚集行为有显著的影响。当其疏水性适宜时,高分子可富集在蛋白表面疏水位点,强化蛋白质分子在水溶液中的分散,从而抑制聚集。高分子还可缠绕在蛋白质分子表面形成限制性空间从而稳定蛋白质的天然结构。     

丙烯腈共聚物序列分布的Monte Carlo模拟

通过Monte Carlo方法,对不同共聚单体的聚丙烯腈组成进行了模拟。通过比较．与文献中提供的实验结果基本一致。同时模拟了衣康酸(1A)、丙烯酸(AA)、甲基丙烯酸(MAA)分别与丙烯腈(AN)在不同配比下共聚物的序列分布,结果表明：在Monte Carlo模型中,可以通过控制单体的配比来控制序列分布,而在实际的合成中,要获得均匀的序列结构,就可以通过降低第二单体投料比法或滴加单体法来实现。     

Monte Carlo模拟对称型三嵌段共聚高分子的吸附

The adsorption behavior of symmetric triblock copolymers, Am/2BnAm/2, from a nonselective solvent at solid-liquid interface has been studied by Monte Carlo simulations on a simple lattice model. Either segment A or segment B is attractive, while the other is non-attractive to the surface. Influences of the adsorption energy,bulk concentration, chain composition and chain length on the microstructure of adsorbed layers are presented.The results show that the total surface coverage and the adsorption amount increases monotonically as the bulk concentration increases. The larger the adsorption energy and the higher the fraction of adsorbing segments, the higher the total surface coverage is exhibited. The product of surface coverage and the proportion of non-attractive segments are nearly independent of the chain length, and the logarithm of the adsorption amount is a linear function of the reciprocal of the reduced temperature. When the adsorption energy is larger, the adsorption amount exhibits a maximum as the fraction of adsorbing segment increases. The adsorption isotherms of copolymers with different length of non-attractive segments can be mapped onto a single curve under given adsorption energy. The adsorption layer thickness decreases as the adsorption energy and the fraction of adsorbing segments increases, but it increhses as the length of non-attractive segments increases. The tails mainly govern the adsorption layer thickness.     

无规共聚高分子溶液相平衡的Monte Carlo模拟

引　言近年来 ,随着计算机硬件能力的不断提高和新的模拟方法的不断涌现 ,对于高分子溶液的相平衡问题的计算机模拟研究取得了很大的进展 ,但大多将注意力放在如何改进模拟方法以获得更长的均聚高分子溶液的相平衡数据 ,以检验Ｆｌｏｒｙ -Ｈｕｇｇｉｎｓ理论、修正Ｆｒｅｅｄ理论等的有效性 .如Ｍａｄｄｅｎ等[1]曾利用蛇行法 (ｒｅｐｔａｔｉｏｎ)和伪动态模拟算法( ｐｓｅｕｄｏｋｉｎｅｔｉｃｓｉｍｕｌａｔｉｏｎａｌｇｏｒｉｔｈｍ)、Ｍａｃｋｉｅ等[2 ]在邻位数Ｚｎ=2 6的格子模型上用Ｇｉｂｂｓ系综法、Ｗｉｌｄｉｎｇ等[3]用键长涨…     

不同工艺嵌段共聚PP结构与性能研究

采用核磁共振碳谱、凝胶渗透色谱和动态力学等多种分析手段对北京燕化石油化工股份有限公司3种不同聚合工艺生产的嵌段共聚聚丙烯产品进行结构与性能研究,分析出不同聚合工艺生产的产品结构、性能的特点及差异,结构对性能的影响,为今后的生产及应用提供参考。     

Monte Carlo模拟随机共聚高分子在固/液界面的吸附行为

用Monte Carlo方法对无规共聚高分子在固液界面的吸附进行模拟,获得了固液界面区吸附链节的分布和吸附构型大小的分布等微观信息,以及总链节和吸附链节密度分布、链附着率、表面覆盖率、吸附量和吸附层厚度等宏观信息.考察了吸附性链节的对比吸附能ε_Aa和无规共聚高分子中吸附性链节比率f对它们的影响.结果表明,界面附近的高分子以尺寸较小的环式和卧式构型分布为主,而尾式构型分布较宽.当f增大时小环式构型迅速增加,卧式构型的分布则变宽.随着ε_Aa和f的增大,链附着率、表面覆盖率和吸附量等均随之增加,而吸附层厚度变薄.     

非选择性溶剂中两嵌段共聚物的吸附及Scheutjens-Fleer理论与Monte Carlo模拟的比较

Systematic comparison between computer simulation results and those predicted by Scheutjens-Fller(SF)self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on attractive surface.It is shown that although SF is a mean-field theory,it can qualitatively describe the adsorption phenomena of diblock copolymers.However,systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-field theory such as random mixing inside a layer and the allowance of direct back folding may be responsible to those deviations.     

Morphologies of diblock copolymer confined in a slit with patterned surfaces studied by dissipative particle dynamics

Diblock copolymers with ordered mesophase structures have been used as templates for nano-fabrication. Unfortunately, the ordered structure only exists at micromete rscale areas, which precludes its use in many advanced applications. To overcome this disadvantage, the diblock copolymer confined in a restricted system with a patterned surface is proved to be an effective means to prohibit the formation of defects and obtain perfect ordered domains. In this work, the morphologies of a thin film of diblock copolymer confined between patterned and neutral surfaces were studied by dissipative particle dynamics. It is shown that the morphology of the symmetric diblock copolymer is affected by the ratio of the pattern period on the surface to the lamellar period of the symmetric diblock copolymer and by the repulsion parameters between blocks and wall particles. To eliminate the defects in the lamellar phase, the pattern period on the surface must match the lamellar period. The difference in the interface energy of different compartments of the pattern should increase with increasing film thickness. The pattern period on the surface has a scaling relationship with the chain length, which is the same as that between the lamellar period and the chain length. The lamellar period is also affected by the polydispersity of the symmetric diblock copolymer. The total period is the average of the period of each component multiplied by the weight of its volume ratio. The morphologies of asymmetric diblock copolymers are also affected by the pattern on the surface, especially when the matching period of the asymmetric diblock copolymer is equal to the pattern period, which is approximately equal to the lamellar period of a symmetric diblock copolymer with the same chain length.     

颗粒堆积现象的计算机模拟

颗粒堆积现象的计算机模拟是为能经济地、有铲地分析和优化不同材料如陶瓷、水泥、医药、粉末冶金、聚合物等的性能,并为设计先进材料朝代一种行之有效的手段,近15年来该领域研究的评述表明颗粒堆积现象模拟,尤其在动态过程方面已取得了一些进展。有些计算机模拟软件已应用于模拟如陶瓷和混凝土的颗粒堆积过程,离散元方法也成功地被应用于模拟过程中。另外,为了简化现有的计算机模拟过程,有关专家用一维Monte Carlo方法来取代复杂的三维方法,同时讨论了现有的颗粒堆积过程模拟方法所存在的问题和局限性。     

Composition dependence of crystallized lamellar morphology formed in crystalline-crystalline diblock copolymers

We have investigated the crystallized morphology formed at each temperature T_c (20 °C ≤ T_c ≤ 45 °C) in double crystalline poly(?-caprolactone)-block-polyethylene (PCL-b-PE) copolymers as a function of composition (or volume fraction of PE blocks ?_PE) by employing small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. When PCL-b-PE with ?_PE ≤ 0.58 was quenched from a microphase-separated melt into T_c, the crystallization of PE blocks occurred first to yield an alternating structure consisting of thin PE crystals and amorphous PE + PCL layers (PE lamellar morphology) followed by the crystallization of PCL blocks, where we can expect a competition between the stability of the PE lamellar morphology (depending on ?_PE) and PCL crystallization (on T_c). Two different morphologies were formed in the system judging from a long period. That is, the PCL block crystallized within the existing PE lamellar morphology at lower T_c (<30 °C) to yield a double crystallized alternating structure while it crystallized by deforming or partially destroying the PE lamellar morphology at higher T_c (>35 °C) to result in a significant increase of the long period. However, the temperature at which the morphology changed was almost independent of ?_PE. For PCL-b-PE with ?_PE ≥ 0.73, on the other hand, the morphology after the crystallization of PE blocks was preserved at every T_c investigated.     

Crystallization behavior of poly(ε-caprolactone) blocks starting from polyethylene lamellar morphology in poly(ε-caprolactone)-block-polyethylene copolymers

The crystallization behavior of poly(ε-caprolactone) (PCL) blocks starting from a solid lamellar morphology formed in advance by the crystallization of polyethylene (PE) blocks (PE lamellar morphology) in a PCL-b-PE diblock copolymer was investigated by differential scanning calorimetry (DSC), small-angle X-ray scattering with synchrotron radiation (SR-SAXS), and polarized optical microscope (POM). The crystallization behavior was quantitatively compared with that of a PCL-block-polybutadiene copolymer, where the crystallization of PCL blocks started from a rubbery lamellar microdomain. DSC and SR-SAXS results revealed that the crystallization rate of PCL blocks in PCL-b-PE increased drastically with decreasing crystallization temperature T_c and the Avrami exponent depended significantly on T_c. SR-SAXS curves during the crystallization of PCL blocks at high T_c showed a bimodal scattering character, that is, the peak position moved discontinuously with crystallization time. At low T_c, on the other hand, no shift of the SAXS peak position was observed. The macroscopic change in morphology was detected only at high T_c by POM observations. These experimental results for the crystallization behavior of PCL blocks in PCL-b-PE all support our previous conclusions obtained by static measurements; the crystallization mechanism at low T_c is completely different from that at high T_c, that is, the PCL blocks crystallize within the PE lamellar morphology at low T_c while the crystallization of PCL blocks at high T_c yields a morphological transition from the PE lamellar morphology into a new solid morphology.     

Morphology of melt-quenched poly(ε-caprolactone)-block-polyethylene copolymers

The morphology of a melt-quenched crystalline-crystalline diblock copolymer, poly(ε-caprolactone)-block-polyethylene (PCL-b-PE), was studied by small-angle X-ray scattering and transmission electron microscopy. The melting behavior of PCL-b-PE was also investigated by differential scanning calorimetry. The melting temperature of PCL blocks, T_m,PCL, was ca. 55 °C and that of PE blocks was ca. 96 °C. Therefore, the PE block always crystallized first during quenching from the microphase-separated melt into various temperatures T_c below T_m,PCL to yield an alternating structure composed of PE lamellae and amorphous layers (PE lamellar morphology), and subsequently the crystallization of PCL blocks started at T_c after some induction period. The PE lamellar morphology was preserved after the crystallization of PCL blocks at low crystallization temperatures (T_c<30 °C), that is, the PCL block crystallized within the PE lamellar morphology. At high crystallization temperatures (45 °C>T_c>30 °C), on the other hand, the crystallization of PCL blocks destroyed the PE lamellar morphology to result in a new lamellar morphology mainly consisting of PCL lamellae and amorphous layers (PCL lamellar morphology). The PE crystals were fragmentarily dispersed in the PCL lamellar morphology.     

Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor

The time development of the surface morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) thin films ‘annealing’ in methanol vapor, a selective solvent for minority P4VP block, was investigated by atomic force microscopy(AFM). For PS-b-P4VP with cylindrical structure in bulk, as annealing time progressed, the surface morphology underwent structural transitions from featureless topography to hybrid morphology of cylindrical and spherical pits, to cylinders, to nanoscale depressions, back to cylinders again. The different film thickness made the number of the transitions observed, at any given annealing time, different. The thicker the film is the more transitions at a given annealing time can be observed. If the film was not thick enough, depressions appeared. For PS-b-P4VP with spherical structure in bulk, it displayed nanoscale depressions with the annealing time increasing. A possible mechanism of the transition of morphologies during solvent annealing was proposed.