硫醇分子链长对氧化还原自组装多层膜电化学行为影响的初步研究(英文)

以烷基硫醇和二茂铁衍生物构建的氧化-还原自组装多层膜为模型体系,研究烷基硫醇分子链长对多层膜电化学行为的影响.实验表明,二茂铁基团和电极之间的电子传递反应速率随两者距离的增加呈现指数级下降的趋势;烷基硫醇分子链长对自组装膜电化学行为的影响于不同情况下表现不同.本实验条件下,当多层膜上的电活性基团与电极比较接近时,长链分子自组装膜呈现较强的电化学响应.而当电极与电活性基团之间的距离较远时,短链烷基硫醇分子自组装膜呈现较强的电化学响应.     

正、叔十二烷基硫醇在铜表面上自组装膜测试

研究了正、叔十二烷基硫醇在铜表面上的自组装及混合自组装成膜情况,并利用交流阻抗和极化曲线电化学方法测试了正、叔十二烷基硫醇在铜表面上自组装膜及混合自组装膜对铜的耐腐蚀性,考察了正十二烷基硫醇自组装膜质量与正十二烷基硫醇溶液的浓度及组装时间的关系。研究结果显示,混合自组装膜的质量及其对铜的耐腐蚀性比仅组装正或叔十二烷基硫醇均有很大的提高。     

图案化自组装膜导向的电沉积

通过图案化自组装膜导向的电沉积制备了聚吡咯(PPy)微结构. 由微接触印刷方法制备图案化自组装膜并作为电沉积的模板. 研究发现, 自组装膜在导向电沉积中在不同的基底上具有不同的作用: 在十二烷基硫醇(DDT)、十八烷基硫醇(ODT)修饰的金基底上和十八烷基三氯硅烷(OTS)修饰的铟锡氧化物玻璃上(ITO), 电沉积主要发生在自组装膜未修饰区, 而在半导体单晶硅表面, PPy沉积在OTS修饰区, 是基底表面的导电性及PPy与基底表面基团相容性共同作用的结果.     

金表面不同链长烷基硫醇自组装单分子膜表面电势的变化规律

从Helmholtz模型出发,对生长在金表面不同链长烷基硫醇自组装单分子膜(SAM)表面电势的变化规律进行了理论研究.利用量子化学软件Gaussian03和MOPAC,讨论了分子偶极矩、相对介电常数以及分子的倾斜角对SAM表面电势的影响.研究表明,不同链长烷基硫醇SAM中分子的倾斜角随烷基链长度的规律性变化是引起SAM表面电势变化的主要原因.从SAM形成机制出发,对金表面不同链长烷基硫醇SAM表面电势的变化规律及其成因提出了新的解释.     

锆离子改善十烷基磷酸组装膜结构及性能研究

利用烷基磷酸、金属锆离子和不锈钢电极表面的相互作用,通过表面自组装,在304不锈钢电极表面分别修饰了单层和双层烷基磷酸自组装膜,采用接触角和极化曲线对修饰电极进行测量.实验表明,双层烷基磷酸修饰膜具有更佳的耐腐蚀性能.     

一种结构新颖的二茂铁硫醇自组装膜的电化学行为

合成二茂铁乙烯基吡啶硫醇(FcC2′PyC4SH,I)及其还原产物二茂铁乙烷基吡啶硫醇(FcC2′PyC4SH,Ⅱ).再利用分子自组装技术在金电极表面形成二茂铁乙烯基吡啶硫醇单分子膜,通过循环伏安法探讨了这种自组装膜与结构相关的电化学响应.     

水介质中吡咯的电化学聚合反应

研究了扫描电位上限对循环伏安法制备聚吡咯膜性能的影响，吡咯在水溶液中于玻碳电极表面化学聚合的起始电位为0．58V，在聚吡咯（Ppy）修饰电极表面聚合的起始电位为0．55V，当聚合电位上限在0．80V以上时，Ppy的氧化还原反应可逆性变差，同时，氧化电位过高将导致Ppy膜导电性能下降；研究了聚合介质对循环伏安法制备导电聚吡咯膜的影响，实时观察了吡咯（Py）聚合过程溶液中质子含量的动态变化，发现Py聚合伴随有质掺杂←→释放过程；结合Ppy膜的元素分析、ESR分析和IR光谱分析，总结出了水介质中电化学聚合高导电性聚吡咯膜的条件。     

流动注射-电化学-表面等离子体激元共振联用技术研究二茂铁硫醇氧化还原结构变化

采用流动注射-电化学-表面等离子体激元共振联用技术研究了11-二茂铁基十一烷基-1-硫醇自组装膜在氧化还原过程中的构型变化.结果表明,二茂铁硫醇在氧化过程中,分子发生了两种结构变化:远离电极表面,烷基链与电极表面的夹角增大;分子上两个平行的戊基环绕着二茂铁-碳轴发生旋转.     

金电极上L-半胱氨酸短链分子自组装单层的电化学性能和拉曼光谱研究

用循环伏安法分别测定了金电极表面L-半胱氨酸(L-Cys)和十二硫醇自组装单分子层的电化学行为, 实验发现虽然单层结构排列致密, 但并不能有效地阻碍铁氰化钾与电极间异相电子转移过程, 同时观察到十二烷基硫醇自组装层能较好地阻碍电子转移作用. 运用表面增强拉曼散射光谱技术, 以十二烷基硫醇作为缺陷探针, 从分子水平上证实了L-半胱氨酸自组装单层的稳定性和致密性.     

聚吡咯薄膜中茜素红S的电化学特性

利用循环伏安法研究了聚合电位和聚合电量对茜素红S掺杂聚吡咯薄膜修饰玻碳电极性质的影响,考察了不同电位范围内修饰电极的电化学特性.发现在茜素红S的氧化还原过程中存在着茜素红S分子与聚吡咯链的相互作用,且这一相互作用敏感于扫描正电位限.基于实验结果,提出了可能的茜素红S在电极表面聚吡咯膜内的氧化还原机理.     

Influence of alkyl chain length on the structure of dialkyldithiophosphinic Acid self-assembled monolayers on gold

We report the formation and characterization of self-assembled monolayers (SAMs) based on dialkyldithiophosphinic acid adsorbates {[CH(3)(CH(2))(n)](2)P(S)SH (n = 5, 9, 11, 13, 15)} on gold substrates. SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. Data show that there is a roughly 60:40 mixture of bidentate and monodentate adsorbates in each of these SAMs. The presence of monodentate adsorbates is due to the numerous and deep grain boundaries of the underlying gold substrate, which disrupt chelation. Comparing the characterization data of dialkyldithiophosphinic acid SAMs with those of analogous n-alkanethiolate SAMs shows that both SAMs follow a similar trend: The alkyl chains become increasingly organized and crystalline with increasing alkyl chain length. The alkyl groups of dialkyldithiophosphinic acid SAMs, however, are generally less densely packed than those of n-alkanethiolate SAMs. For short alkyl chains (hexyl, decyl, and dodecyl), the significantly lower packing densities cause the alkyl chains to be liquid-like and disorganized. Long-chain dialkyldithiophosphinic acid SAMs are only slightly less crystalline than analogous n-alkanethiolate SAMs.     

Novel Cross‐Linked Conducting Polythiophene with Yellow‐Green‐Light‐Emitting Properties and Good Thermal Stability

A novel conjugated polythiophene derivative with polymethacrylate attaching to the polymer backbone via an alkyl spacer was successfully synthesized. A methacrylate‐substituted thiophene monomer, 3‐(hexyl methacrylate)thiophene was prepared and polymerized by free radical polymerization, followed by an electrochemical polymerization. The resulting polymer as a yellow‐green‐light emitter, has potential applications in photoelectronics area.     

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold--long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.     

Effect of Alkyl Aluminums on Ethylene Polymerization Reactions with a Cr‐V Bimetallic Catalyst

The effect of introducing various types of alkyl aluminums directly into the catalyst and/or in the polymerization process as cocatalyst on the efficiency of a Cr‐V bimetallic catalyst for ethylene polymerization is systematically investigated. Results indicate that polymerization activity, kinetic behavior, and polymer properties of the Cr‐V catalyst are strongly affected by using alkyl aluminums in different stages of polymerization, due to the different responses and sensitivities of the two metal centers to alkyl aluminum. When employed as cocatalyst, triisobutyl aluminum gives high activity and polyethylene with relatively low molecular weight, while diethylaluminum chloride cocatalyzes the production of ultra‐high molecular weight polyethylene but with very low activity. On the other hand, the pre‐reduction of the bimetallic catalyst by alkyl aluminums has a marked promotion effect on catalyst efficiency. It is suggested that the addition of alkyl aluminum to the catalyst and to the reactor as cocatalyst are more or less equivalent in their effects on the improvement of polymerization activity, but they behave in different ways to affect polymer properties.     

Scanning electrochemical microscopy. 59. Effect of defects and structure on electron transfer through self-assembled monolayers

Electron transfer (ET) rate kinetics through n-alkanethiol self-assembled monolayers (SAMs) of alkanethiols of different chain lengths [Me(CH2)nSH; n=8, 10, 11, 15] on Au and Hg surfaces and ferrocene (Fc)-terminated SAMs (poly-norbornylogous and HS(CH2)12CONHCH2Fc) on Au were studied using cyclic voltammetry and scanning electrochemical microscopy (SECM). The SECM results allow determination of the ET kinetics of solution-phase Ru(NH3)63+/2+ through the alkanethiol SAMs on Au and Hg. A model using the potential dependence of the measured rate constants is proposed to compensate for the pinhole contribution. Extrapolated values of koML for Ru(NH3)63+/2+ using the model follow the expected exponential decay (beta is 0.9) for different chain lengths. For a Fc-terminated poly-norbornyl SAM, the standard rate constant of direct tunneling (ko is 189+/-31 s(-1)) is in the same order as the ko value of HS(CH2)12CONHCH2Fc. In blocking and Fc SAMs, the rates of ET are demonstrated to follow Butler-Volmer kinetics with transfer coefficients alpha of 0.5. Lower values of alpha are treated as a result of the pinhole contribution. The normalized rates of ET are 3 orders of magnitude higher for Fc-terminated than for blocking monolayers. Scanning electron microscopy imaging of Pd nanoparticles electrochemically deposited in pinholes of blocking SAMs was used to confirm the presence of pinholes.     

Forces between thiolate-modified gold surfaces in a melt of end-functionalized polymers

To better understand surface forces across polymer melts, we measured the force between two chemically well-defined solid surfaces in a melt of polymer chains with a functional end group. As for surfaces, we used self-assembed monolayers (SAMs) of alkyl thiols with different end groups (methyl, amino, and hydroxyl) on gold. The polymer was a hydroxyl-terminated polyisoprene. To measure the force, an atomic force microscope was used. Between methyl-terminated SAMs, a weak and short-range repulsion was detected. Between hydroxyl or amino-terminated SAMs, a strong and long-range repulsion was observed up to distances of 16 nm. This indicates that the hydroxyl group of the polymer binds to the hydroxyl or amino groups of the SAMs. It forms a brush-like structure, which leads to steric repulsion. On amino-terminated SAMs, force-versus-distance curves on approach and retraction were monotonically repulsive and reversible. With hydroxyl-terminated SAMs, a jump was observed on approach when the load exceeded a certain threshold. On retraction, an adhesion had to be overcome. We interpret the jump as a rupture of the polymer layer. It indicates that the kinetics of bond and brush formation is faster on OH-SAMs than on NH2-SAMs.     

Effect of polymerization rate on the polyethylene structure obtained with a high activity catalyst system

The effect of polymerization rate on polyethylene structure, using magnesium reduced titanium tetrachloride catalysts together with the usual aluminium alkyl activator, is described. It is shown that the polymer bulk density and the nascent super-molecular structure formed during ethylene polymerization depends upon the rate of polymerization. The results indicate that, with increasing polymerization rate, the catalyst active sites produce polymer with different densities. One possible explanation for this phenomenon lies in considering the inhibition of crystallization by high polymerization rates. Experimental results on different polymer morphologies are discussed. Finally models for the structure of polymer particles are considered briefly.     

Cross-linking copolymers of acrylates’ gel electrolytes with high conductivity for lithium-ion batteries

The cross-linking gel copolymer electrolytes containing alkyl acrylates, triethylene glycol dimethacrylate, and liquid electrolyte were prepared by in situ thermal polymerization. The gel polymer electrolytes containing 15 wt% polymer content and 85 wt% liquid electrolyte content with sufficient mechanical strength showed the high ionic conductivity around 5?×?10^?3 Scm^?1 at room temperature. The gel electrolytes containing different polymer matrices were prepared, and their physical observation and conductivity were discussed carefully. The cross-linking copolymer gel electrolytes of alkyl acrylates with other monomers were designed and synthesized. The results showed that copolymerization can improve the mechanical properties and ionic conductivities of the gel electrolytes. The polymer matrices of gels had excellent thermal stability and electrochemical stability. The scanning electron microscope analysis showed the gel electrolyte was the homogeneous structure, and the cross-linking polymer host was the porous three-dimensional network structure, which demonstrated the high conductivity of the gel electrolytes. The gel polymer Li-ion battery was prepared by this in situ thermal polymerization. The cell exhibited high charge-discharge efficiency at 0.1 C. The results of LiFePO4-PEA-Li cell and graphite-PEA-Li cell showed that gel polymer electrolytes have good compatibility with the battery electrodes materials.     

电化学聚合漆酚铜配合物的结构及其催化性能

 将电化学聚合法得到的聚合漆酚（EPU）与氯化铜的异丙醇溶液作用制成了电化学聚合漆酚铜配合物（EPU－Cu2＋）,并用顺磁共振波谱、红外光谱、X射线光电子能谱、动态机械热分析和原子发射光谱等手段进行了表征．结果表明,该配合物中每个铜离子与EPU分子中二个链节单元的羟基发生配位,铜含量达8．63％．实验结果还表明,该配合物在Na2SO3的水体系（pH＝7）中能催化引发MMA按自由基反应历程进行聚合．     

Mapping of defects in self-assembled monolayers by polymer decoration

A new method mapping the defects in self-assembled monolayers (SAMs) is described. The method is based on electrochemical polymerisation of nonconductive tyramine in defect sites of a monolayer and subsequent visualisation of the polymer structures by atomic force microscopy (AFM). SAMs of hexadecanthiol (HDT) on gold prepared by deposition from solution and microcontact printing were used as a model for this study. The method allows easy mapping of defects on monolayers and provides information about their shape, size, size distribution, defect density and spatial distribution. Comparative electrochemical characterisation of defects in SAMs before and after polymerisation shows that polymer growth occurs on the sites of uncovered gold. The approach should be applicable for the characterisation of defects in other types of ultra-thin organic films on conducting surfaces.