【作者】 郭文娟；

【导师】 陈慎豪；

【作者基本信息】 山东大学 ， 物理化学， 2007， 博士

【摘要】 自组装膜（Self-assembled films）是活性分子通过化学键相互作用自发吸附在固-液或气-固界面而形成的具有一定取向、排列紧密的有序分子膜，是热力学稳定体系。固体暴露在活性分子的溶液或气氛中，便可自发形成自组装膜，它不要求无水或真空等特殊环境，也不需要特殊仪器。自组装膜因其在室温和常压条件下即可形成，且制备方法简单易行，形成的膜致密有序，所以作为一种方便的成膜方法在工业和生活中具有广泛的应用前景，领域涉及到金属缓蚀、传感器制备、纳米材料科学、生物化学、医学等。特别是在金属腐蚀与防护领域，自组装膜技术已经成为一种新的金属表面修饰技术，发挥着越来越重要的作用。铜、铁是重要的商用金属，被广泛地应用于建筑业、化学工业、电子工业、航空航天等领域，但它们的化学性质较为活泼，暴露在空气或水中很容易被氧化。因此铜、铁的腐蚀与防护问题是腐蚀科学领域一个亟待解决的重要问题，已经引起科学家们的广泛关注。从金属腐蚀与防护的研究角度，选择合适的有机化合物在铜、铁表面进行自组装，并进一步研究各种因素对成膜效果的影响，从而改进自组装实验技术，具有重要的理论指导意义和应用价值。本论文的研究目的是找出合适的分子，改善实验技术，在铜、铁表面制备优良的具有缓蚀功能的自组装膜，有效地将金属与外界环境隔离开来，达到对金属腐蚀防护的效果。并研究各种成膜因素，例如浓度、自组装时间等对缓蚀效率的影响，从而寻找到一条较好的自组装成膜途径。实验中选用磷酸酯类化合物，在经过预处理的铜、铁金属表面进行自组装，通过电化学实验技术测试了腐蚀电位、电荷传递电阻、腐蚀电流密度、双电层电容等参数，从而得到自组装膜在电极上的表面覆盖度，反映自组装膜覆盖的铜、铁电极在腐蚀性溶液中的缓蚀效果。并用X射线光电子能谱（XPS）和傅里叶变换红外光谱（FT-IR）等表面分析技术对膜的成分进行测定，验证有机物在电极表面的吸附行为。扫描电子显微镜（SEM）观测了自组装膜覆盖的电极表面和空白电极表面的形貌图，可以直接观测到膜对基底的保护效果。分子模拟方法在分子水平上提供了自组装成膜分子在电极表面的吸附信息，进一步解释了实验结果，还转而为选择、设计和合成一系列新型、低毒的自组装膜化合物提供一定的理论性指导。本实验在自组装过程中，首次添加磁场条件，突破了传统的仅采用浸泡自组装成膜的技术，改善了自组装膜的质量，从而为拓宽自组装膜技术提供了一个新思路。电化学实验测试研究了磁场强度对自组装膜成膜效果的影响。测试结果表明，磁场的添加，大大增加了自组装膜的电荷传递电阻，有利于形成较为完善的自组装膜，提高膜的缓蚀效率。且缓蚀效率随磁场强度的增加而增大。本实验还制备了混合自组装膜。实验结果证明，混合膜的形成，有利于改善单一自组装膜中存在的缺陷，有效提高了自组装膜的缓蚀效率。论文的主要研究内容、研究结果如下：1．铜表面自组装磷酸三乙酯（TEP）和磷酸三苯酯（TPP）膜铜电极在7 mol dm^-3的硝酸溶液中刻蚀后，获得洁净的铜表面。在预处理过的铜电极表面分别制备TEP和TPP自组装膜。电化学阻抗谱测试结果显示，随着组装时间的延长，电荷传递电阻增大，双电层电容减小，常相位角元件的指数n值增大，从而说明膜的覆盖度增大，缓蚀效率增加。具体来说，TEP和TPP分子在铜上自组装膜的形成过程可以分为最初的快速吸附和随后的慢速重排过程。在最初的1小时内，自组装膜的电荷传递电阻快速增加，TEP自组装膜的覆盖度达到了81.0％，TPP自组装膜的覆盖度达到了85.4％。随后的时间段内，膜的覆盖度继续增加，但增加速度缓慢。从1小时到4小时，再到12小时，TEP自组装膜的覆盖度增加为90.2％，93.8％，而TPP自组装膜的覆盖度也增加为88.1％，96.5％。自组装时间为24小时时，膜的覆盖度反而略有减小，TEP自组装膜的覆盖度为85.3％，TPP自组装膜的覆盖度达为93.1％。总的来说，在相同的自组装时间下，TEP′自组装膜和TPP自组装膜相比，后者的致密度和缓蚀性能都高于前者。这可能是由于TPP分子中含有苯环结构。苯环为平面结构，占有较大的空间，使TPP分子在铜电极表面的覆盖度较大。X射线光电子能谱（XPS）测试出分子中相关的元素峰，证明了有机物在铜电极表面的吸附行为。量子化学从头算方法计算了TEP和TPP分子的Milliken电荷分布。结果表明，TEP分子中，处于P=O键中的氧原子的电荷为—1.192 e，三个—CH₃基团中的碳原子电荷分别为—1.233 e，—1.234 e和—1.235 e。考虑到—CH₃中的碳原子被氢包围的情况，所以推测TEP分子很有可能是通过P=O键中的氧原子向铜的空轨道提供电子而吸附在铜电极表面的。而对于TPP分子，结果显示，P=O键中的氧原子的电荷密度是—1.164 e，比分子中其它原子的电荷密度更负，所以TPP也是通过P=O键中的氧原子向铜的空轨道提供电子而吸附在铜电极表面的。还分别计算出TEP和TPP分子的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）的能量。TEP分子的HOMO为—10.516 eV，LUMO为—3.744 eV；而TPP分子的HOMO为—10.010 eV，LUMO为—5.904 eV。与TEP分子相比，TPP分子的HOMO能量相对较高，LUMO能量相对较低，从理论上解释了TPP较TEP分子更易吸附在铜表面的原因。实验和理论计算结果均表明，TPP自组装膜具有较好的缓蚀效率。2．铁表面组装磷酸三苯酯（TPP）和二（2-乙基己基）磷酸酯（BEP）膜在铁电极表面分别制备TPP和BEP自组装膜。改变TPP和BEP溶液的浓度和组装时间，比较自组装膜的缓蚀效率的变化。电化学测试结果表明，两种自组装膜均可有效的抑制铁在0.5 mol dm^-3 H₂SO₄溶液中的腐蚀反应，且缓蚀效率随磷酸酯溶液浓度和组装时间的增加而增加。电化学阻抗谱显示，1×10^-5mol dm^-3TPP自组装膜的电荷传递电阻在最初30 min内快速增大，4 h内即可达到最大值，此时膜的覆盖度为78.1％，此后保持恒定。浓度增大为1×10^-3 mol dm^-3时，同样在最初的30分钟内膜的电荷传递电阻快速增大，2 h内即可增大到最大值，此时膜的覆盖度为79.6％，此后电荷传递电阻略有下降。而1×10^-5 mol dm^-3和1×10^-3 mol dm^-3 BEP自组装膜的电荷传递电阻均随组装时间的增加而逐渐增加。在相同的浸泡时间下，1×10^-3 mol dm^-3 TPP（或BEP）溶液中形成的自组装膜，其缓蚀效率要高于1×10^-5 mol dm^-3 TPP（或BEP）溶液中形成的自组装膜的缓蚀效率。极化曲线测试结果显示，TPP和BEP自组装膜覆盖的铁电极，其腐蚀电位正移，且阳极和阴极腐蚀电流密度均减小，说明膜对铁的腐蚀有抑制作用，且腐蚀电流密度随组装时间和浓度的增加而减小。傅立叶转换红外光谱（FT-IR）测试结果显示，谱图中出现的基团特征峰，均相对于TPP和BEP分子中的官能团，证明了TPP和BEP吸附在铁表面。分子模拟方法提供了TPP和BEP分子在铁上吸附的信息。结果显示，TPP和BEP吸附在铁基底后，均发生了一定程度的倾斜。3．磁场对自组装膜缓蚀效率的影响自组装过程中添加了磁场，首次研究了磁场强度对自组装成膜效果的影响。选取铜上自组装TEP膜体系进行实验，TEP浓度为1×10^-3 mol dm^-3，组装时间为1小时。电化学测试结果显示，与无磁场的情况相比，外加磁场有利于提高自组装膜对铜的缓蚀效率。且随磁场强度的增加，缓蚀效率增加。磁场强度为80 mT和160 mT时，TEP自组装膜的缓蚀效率分别增大为94.2％和97.6％，而无外加磁场时，TEP自组装膜的缓蚀效率仅为81.0％。据推测，TEP为极性分子，在磁场中定向排列，外加磁场有利于TEP分子在铜电极表面形成有序致密的膜，从而大大提高自组装膜的缓蚀效率。利用外加磁场的方法是一种全新的思路，它改善了单一浸泡的自组装膜实验技术，具有一定的研究和应用价值。4．混合自组装膜的制备为了改善单一自组装膜的缺陷，实验中制备了混合自组装膜。选取阳离子表面活性剂，十六烷基三甲基溴化铵（CTAB）与TEP协同作用，在铜电极表面形成混合自组装膜。先将铜电极浸入1×10^-3 mol dm^-3 TEP乙醇溶液1小时，形成TEP单一自组装膜，然后放入1×10^-3 mol dm^-3 CTAB的水溶液中，组装1小时或者24小时，形成TEP和CTAB混合自组装膜。电化学阻抗谱显示，混合膜的电荷传递电阻要大于单一TEP自组装膜的电荷传递电阻。计算出的单一TEP自组装膜的覆盖度为81.0％，而和CTAB形成混合自组装膜后覆盖度最大可达到99.4％。这说明和单一的TEP自组装膜相比，CATB和TEP协同形成的混合自组装膜对铜有更好的防护作用。更多还原

【Abstract】 Self-assembled films are ordered and dense molecular assemblies formed by the spontaneously chemical adsorption of the active molecules on solid surface. They are the thermodynamically steady system. When the solid is exposed to the solution or gas with the active molecules, self-assembled films can be formed automatically. They do not need the environments of no water or vacuum and not need any special instrument. Self-assembled films are ideal models for studying some complex phenomena concerning about the surfaces, since their structures are orderly and can be designed flexibly. They have the widely applications in many fields, such as biochemistry, nano-materials, metal corrosion and sensors. Because of their densely packed and stable structures, self-assembled films play an important role in the field of surface modification, especially in the field of the inhibitive corrosion of metals.Copper and iron are important metals which are widely used in buildings, chemistry, electric industry, and etc. But their chemical property is very active, and they tend to be oxygenated when exposed to air or water. Thus, the corrosion inhibition of copper and iron has become an important research subject. The technique of self-assembly is practically and theoretically advantageous in the protection of metals. From the aspect of corrosion inhibition of metals, it is very necessary to choose some appropriate organic compounds to self-assemble on the metal surface.The purpose of our research is to find some proper self-assembled systems as the barrier layers which can efficiently insulate the metal from the external surroundings. Phosphates were selected to prepare self-assembled films on copper and iron surfaces in order to protect the metals against corrosion. The inhibitive effect was measured by electrochemical methods, such as electrochemical impedance spectroscopy and polarization curves. The surface analytical methods, such as X-ray photoelectron spectroscopy （XPS） and Fourier transform infrared spectroscopy （FT-IR） were used to confirm the action of adsorption by detecting the elements or the group in the organic molecules adsorbed on the metal surface. In order to find a better way for corrosion inhibition of metal, we have investigated the effects of some factors, such as concentration and immersion time on the inhibitive efficiency （IE）.An external magnetic field was first applied during the process of self-assembly. Results show that the addition of the magnetic field can improve the quality of the self-assembled films markedly. With the increase of field strength, the IE increases. The reason may be that the external magnetic field makes the polar TEP molecules range more orderly and causes the film denser.Moreover, a kind of surfactant, cetyltrimethyl ammonium bromide （CTAB） was used to prepare the mixed films with TEP. Results show that the mixed films have the better quality than the films made of the single molecules.Quantum chemical calculations can provide some information about the process of adsorption of molecules on the metal surface at the molecular level. The results of quantum chemical calculations are consistent with the results of the experiments. Quantum chemical calculations can not only explain the results of experiment, but also be guidance for selecting or synthesizing the proper compounds for self-assembled films with lower toxicity. The main contents and results of this dissertation can be summarized as the following:1. Self-assembled films of triethyl phosphate （TEP） and triphenyl phosphate （TPP） on the copper surfaceCopper electrode was immersed in 7 mol dm^-3 HNO₃ to obtain a fresh surface. Then it was immersed in 1×10^-3 mol dm^-3 TEP ethanol solutions or TPP ethanol solutions, respectively. After the designed time, TEP or TPP films were formed on the copper electrode. Results of electrochemical impedance spectroscopy （EIS） show that the charge transfer resistance (R_ct) increases with the increase of the immersion time. At the initial period （1 h）, R_ct of the films increases quickly. The coverage （θ） of TEP gets to 81.0% and that of TPP gets to 85.4%. During the subsequent period, 8 goes on increasing, but the increasing rate is not as fast as before. Form 1 h to 4 h, and to 12 h,θof TEP gets to 90.2%, 93.8% andθof TPP gets to 88.1%, 96.5%. But when the immersion time is 24 h,θof TEP gets to 85.3% and that of TPP gets to 93.1%. At this time, 9 decreases instead. At the same immersion time, IE of TPP is higher than that of TEP. The reason is that there are planar phenyl groups in TPP molecules and phenyl groups can occupy larger space, which can cover more surface area of copper electrode. Compositions of the films were analyzed with X-ray photoelectron spectroscopy （XPS）. The appearance of peaks of elements can confirm the adsorption of TEP on copper. The Milliken charge distribution of TEP and TPP molecules were obtained by ab initio calculations. Results show that the charge of O atom of P=O bond is more negative, so TEP and TPP molecules may be adsorbed on the copper surface by O atom of P=O. At the same time, the energies of the highest occupied molecular orbit （HOMO） and the lowest unoccupied molecular orbit （LUMO） of TEP and TPP molecules were compared. The energies of HOMO and LUMO of TEP molecule are -10.516 eV and -3.744 eV, respectively. The energies of HOMO and LUMO of TPP molecule are -10.010 eV and -5.904 eV, respectively. Compared with TEP molecule, TPP molecule has the higher energy of HOMO and the lower energy of LUMO, which is the reason that TPP adsorbs on the copper surface more easily. Thus TPP has the better inhibitive effect.2. Self-assembled films of triphenyl phosphate （TPP） and bis-（2-ethylhexyl） phosphate （BEP） on the iron surfaceIron electrode was immersed in TPP and BEP ethanol solutions for designed time to prepare self-assembled films. IE and 9 of the self-assembled films were calculated from the polarization curves and EIS, respectively. Results show that these two kinds of self-assembled films can inhibit the corrosion of iron in 0.5 mol dm^-3 H₂SO₄ efficiently. Results of EIS show that R_ct increases with the increase of the immersion time and the concentration of phosphates. As for the self-assembled film formed in 1×10^-5 mol dm^-3 TPP solutions, R_ct increases quickly in the initial 30 min. When it increases to 4 h, R_ct gets to the maximum value andθis 78.1% at this time. Thenθremains constant. As for self-assembled films formed in 1×10^-3 mol dm^-3 TPP solutions, R_ct increases quickly in the initial 30 min, but will get to the maximum value only in 2 h. At this time,θis 79.6%. Then it decreases slightly. As for self-assembled films formed in 1×10^-5 mol dm^-3 or in 1×10^-3 mol dm^-3 BEP solutions, R_ct increases gradually during 24 h. At the same time, the inhibitive effect of self-assembled films formed in 1×10^-3 mol dm^-3 TPP （BEP） solutions is better than that of self-assembled films formed in 1×10^-5 mol dm^-3 TPP （BEP） solutions. Polarization curves of iron with and without self-assembled films of TPP or BEP were also used to test the quality of films. Compared with the naked iron electrode, the corrosion potential of the iron electrode with self-assembled films removes in the positive direction. And when the iron electrode is covered with phosphate films, both the cathodic current density and the anodic current density reduce markedly, which indicates that both the anodic and the cathodic electrochemical processes are inhibited. Results of electrochemical measurements show that the self-assembled films have protected the iron electrode against corrosion to some extent. The groups of TPP and BEP molecules were detected by Fourier transform infrared （FT-IR） spectroscopy. Results show that the characterization peaks corresponding to the groups in the compounds were all detected and this confirms the appearance of TPP or BEP on the iron surface. In order to explain the experimental results, molecular simulations were used to provide some information about the process of adsorption of TPP or BEP on iron surface at molecular level. It shows that TPP and BEP molecules tilted at the iron surface after adsorption.3. The effect of the external magnetic field on the self-assemblyCopper electrode was immersed in 1×10^-3 mol dm^-3 TEP ethanol solutions for 1 h. The magnetic field was first applied during the process of self-assembly. Compared with the self-assembled films formed without the external magnetic field, the films formed under the condition of adding the magnetic field have the better quality. Moreover, IE increases with the increase of magnetic field intensity. When the field intensity increases to 80 mT and to 160 mT, IE increases to 94.2% and 97.6%, respectively. While IE is only 81.0% without the magnetic field. It is presumed that the magnetic field can affect the arrangement of the polar molecules, TER And TEP self-assembled on the copper surface more orderly. So the films become denser and more stable.4. The mixed filmsIn order to improve the quality of self-assembled films, a kind of mixed films made of TEP and cetyltrimethyl ammonium bromide （CTAB） was prepared on the copper surface. First, copper electrode was immersed in 1×10^-3 mol dm^-3 TEP ethanol solutions for 1 h to form the single self-assembled films. Then TEP films were modified with CTAB. The immersion time in 1×10^-3 mol dm^-3 CTAB solutions is 1 h or 24 h. Results of electrochemical measurements show that compared with TEP films, R₍ct0 of the mixed films increases and the current density reduces.θof the mixed films increases to 99.4%, which is more than 81.0%, that of the single films. These results indicate that the mixed films made of TEP and CTAB have the better corrosion inhibition for copper.更多还原