【作者】 贾近；

【导师】 黄玉东；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2009， 博士

【摘要】 本文采用分子自组装方法对炭纤维（CF）表面进行改性,从而在CF复合材料界面实现可调控、定向有序排列的界面相。并通过分子动力学（MD）模拟方法,在分子水平上探索了炭纤维聚合物基复合材料的界面作用规律,这对于推动我国复合材料界面科学理论及表面处理技术的发展,具有重要的理论和实际意义。针对环氧树脂（EP）,选用金表面自组装硫醇分子体系。采用分子模拟方法探讨了不同链长、不同末端官能团的硫醇分子对分子自组装膜（SAMs）/Au（111）与环氧树脂界面性能的影响,并且通过实验对模拟结果进行了验证。在分子模拟部分,采用密度泛函理论（DFT）研究了甲基硫醇（MT）及2-巯基乙醇（ME）在Au（111）表面的吸附结构,结果表明其最稳定的吸附位置为bri-fcc位。在DFT研究基础上,建立了满覆盖率下的功能化烷基硫醇分子S（CH₂）_nX（X =-OH、-NH₂、-COOH,n=1¹7）在Au（111）表面的初始吸附结构,并采用MD模拟方法对其排列结构进行了研究。模拟结果表明,不同末端官能团的SAMs结构随链长的变化趋势是相似的,并且三种SAMs的稳定性强弱顺序为:S（CH₂）_nCOOH>S（CH₂）_nNH₂>S（CH₂）_nOH。以Au（111）表面自组装S（CH₂）_nX的MD模拟结果为初始表面模型,建立了SAMs/Au（111）与环氧树脂的界面模型,通过模拟退火法,寻找最低能量的界面结构。模拟结果表明,对三种不同的界面体系,界面结构最稳定时的自组装分子链长分别为n=10、11。这三种界面体系的稳定性顺序为:S（CH₂）_nNH₂/EP>S（CH₂）_nCOOH/EP>S（CH₂）_nOH/EP。采用化学镀金方法使CF表面金属化,然后在其表面自组装上5种硫醇分子[S（CH₂）_nOH（n=2,6,11）、S（CH₂）₂NH₂、S（CH₂）₂COOH],考察不同的自组装分子对CF/EP复合材料界面剪切强度（IFSS）的影响。实验结果表明,对于S（CH₂）_nOH,链长n为11的复合材料的IFSS比n=2、6的复合材料的IFSS要高,并且随着链长的增加,IFSS先减小后增大。而对于同一链长、不同末端官能团的硫醇分子,其复合材料IFSS的大小顺序为:S（CH₂）₂NH₂>S（CH₂）₂COOH>S（CH₂）₂OH。这一结果与本文MD模拟结果完全一致。针对聚芳基乙炔（PAA）树脂,选用羟基化表面/有机硅烷偶联剂的自组装体系。采用MD方法重点研究了偶联剂链长对CF/PAA界面性能的影响。模拟结果表明,CF/PAA界面作用能随偶联剂分子链长的增大,呈现先减小后增大的趋势;当n=100时,界面能最低,界面结构最稳定。CF/PAA界面作用能与硅烷偶联剂的分子链与PAA分子之间发生的缠结作用以及偶联剂碳链在炭纤维表面的覆盖率有关。采用臭氧化法对CF表面进行硅烷偶联剂改性,并对自组装不同链长偶联剂（n=1¹8）的CF/PAA复合材料进行层间剪切强度（ILSS）和IFSS测试。实验结果表明,随着偶联剂碳链长度的增加,复合材料的界面强度逐渐增大。对其层间剪切断口的扫描电子显微镜（SEM）分析同样表明复合材料的界面粘结性能随碳链长度的增加而改善。对CF/PAA复合材料,其界面性能提高的主要原因是自组装于炭纤维表面的偶联剂分子链和PAA树脂的分子链之间发生的缠结作用,并且这种作用在n≤18时随着偶联剂分子链长度的增加而增强,这一规律与本文MD模拟得到的规律是一致的。更多还原

【Abstract】 In this work, the molecular self-assembled technique was applied on the interface modification of carbon fiber reinforced composites, thus the controllable interphase could be obtained. The interfacial functionary mechanism of the composites was studied by molecular dynamics simulation at molecular level. This research has great significance, both in theory and practices, for developing the surface modification methods of carbon fiber and clarifying the mechanisms of interfacial interaction.For epoxy resin （EP）, the composite interphase was modified by thiols/Au self-assembled systems. First, the influence of the chain length and end functional groups on the interfacial properties between the SAMs/Au（111） and epoxy resin were studied by molecular simulations. Then, the CF surface was Au-plated, and the simulation results were verified by experiments.In the part of molecular simulations, the structures of methanethiol （MT） and 2-mercaptoethanol （ME） adsorbed on Au（111） surface were studied firstly by density functional theory （DFT） based on the first principle. The results indicated that the most stable adsorption site of the thiols was bri-fcc site. Based on the DFT study, the initial models of S（CH₂）_nX（X =-OH、-NH₂、-COOH,n=1¹7） on Au（111） surface atΘ=1 were built. The packing structures of the SAMs on Au（111） were studied by molecular dynamics （MD） method. And the influence of the chain length and end functional groups on the structure of SAMs was discussed. The simulation results indicate that the change trend of the SAMs with different end groups is almost the same. And the stability of the three types of SAMs is:S（CH₂）_nCOOH>S（CH₂）_nNH₂>S（CH₂）_nOH.The MD simulation results of the S（CH₂）_nX/Au（111） were used as the initial surface models, and then the interfacial models of SAMs/Au（111） and epoxy resin were prepared. The interface structures were calculated by the simulated annealing methods. The simulation results indicate that the chain length, n, is 10, 11 when the interface structures are stable. The stability of different system is: S（CH₂）_nNH₂/EP>S（CH₂）_nCOOH/EP>S（CH₂）_nOH/EP.The surface of the CF was metallized by the electroless Au plating. Then different types of thiols[S（CH₂）_nOH（n=2,6,11）,S（CH₂）2NH₂,S（CH₂）2COOH] were self-assembled on the Au-plated CF surface, and the effects of the thiols on interfacial shear strengths （IFSS） of CF/EP composites were investigated. The results indicate that the IFSS of S（CH₂）11OH/EP comopsites is higher than those of S（CH₂）₂OH/EP and S（CH₂）6OH/EP composites. And the IFSS decreases firstly and then increases with the increase of the chain length. The order of the IFSS of the S（CH₂）₂X/EP composites is: S（CH₂）₂NH₂ > S（CH₂）₂COOH > S（CH₂）₂OH. The experiment results are in good accordance with the simulation results.For polyarylacetylene （PAA） resin, composite interphase was modified by hydroxylated surface/organic silane derivatives self-assembled systems. The effect of chain length on the interfacial properties of the composites was studied by MD simulation. The simulation results indicate that the interface energy decreases firstly and then increases gradually with the increase of the chain length. The interface energy is the lowest and the interface structure is most stable when n=100. The interface energy is determined by the entanglement interaction between the molecular chains of coupling agents and the PAA resin, and the coverage of the molecular chains of coupling agents on the CF surface.The surface of CF was modified by silane coupling agent using ozonization methods, and the interlaminar shear strengths （ILSS） and IFSS of the CF/PAA composites were tested. The results indicate that the properties of the composites are improved with the increase of the chain length. The analysis of the ILSS fracture morphology also indicates that the interfacial bond behavior is improved with the increase of the chain length. For the CF/PAA composites, the improvement of the interfacial properties is due to the interactions between the molecular chains of the coupling agents and PAA resin, and the interactions increase with the increase of the chain length. The experiment results prove that the MD simulation methods in this paper are available.更多还原