两种侧链偶氮聚电解质自组装膜中生色团取向研究

用偏振紫外光谱研究了两种侧链偶氮聚电解质静电逐层自组装膜中偶氮生色团的初始取向 .讨论了不同的组装条件对自组装膜中偶氮生色团取向的影响 .进一步探讨了偶氮聚电解质自组装膜的结构特点 .研究表明 ,侧链偶氮聚电解质自组装膜中的偶氮生色团存在一定程度的面内取向 ,自组装的各种影响条件和聚合物结构等 (pH值、侧链柔性间隔基团长度、以及偶氮生色团官能度等 )与自组装膜中偶氮生色团的面内取向程度存在一定的相关性 .通过研究偶氮生色团的取向和影响因素 ,可以深入认识侧链偶氮聚电解质的自组装行为     

端基对侧链型偶氮聚电解质自组装膜内生色团取向的影响

用偏振紫外光谱研究了 4种带有不同端基的侧链型偶氮聚电解质静电逐层自组装膜中偶氮生色团的初始取向 .讨论了不同的端基对偶氮生色团在自组装膜中初始取向的影响 .进一步探讨了偶氮聚电解质自组装膜的结构特点 .研究表明 ,侧链型偶氮聚电解质自组装膜中偶氮生色团普遍存在一定程度的沿面取向 .偶氮生色团所带端基的类型对其在自组装膜中的取向程度有较大的影响 ,这主要取决于偶氮生色团与聚阳离子基底的电荷相互作用和极性相互作用等 .对偶氮生色团在水溶液中能形成H 聚集体的自组装膜来说 ,H 聚集体对生色团取向也有一定的影响 .结果表明 ,在制备需控制生色团取向性的自组装膜时 ,要考虑生色团上的不同端基对取向的影响     

在N,N-二甲基甲酰胺/水混合溶剂中制备偶氮聚电解质自组装膜

利用静电吸附逐层自组装方法在有机溶剂N,N二甲基甲酰胺(DMF)和H2O的混合介质中制备非水溶性偶氮聚电解质自组装多层膜.研究了DMF和H2O的配比对自组装膜生长、结构与表面形态的影响.结果表明,DMFH2O的混合溶剂是非水溶性偶氮聚电解质自组装的理想介质,二者之间的配比对自组装膜的生长速度,膜的结构以及表面形态均有显著影响.随着混合溶液中DMF含量的升高,自组装膜的生长速度逐渐下降但线形生长关系越来越好,所得自组装膜中偶氮生色团的H聚集程度逐渐下降,而且自组装膜的表面越来越平整.     

光响应性偶氮聚电解质自组装研究

将3种侧链带有不同偶氮生色团的聚电解质,用逐层浸渍的方法使其组装成多层膜.利用原子力显微镜(AFM)研究了自组装膜的表面形貌以及随着组装层数增加的变化.详细研究了在紫外光的照射下,薄膜内偶氮生色团由反式到顺式构型的光响应转变,以及在暗室中由顺式回复到反式构型的回复特性.与自组装膜的光响应性和相应的旋涂膜进行比较发现,其中的PNAPE/PDAC自组装膜没有明显的光色效应,而PEAPE/PDAC,PPAPE/PDAC具有明显的光色效应.在暗室中,随生色团的结构不同和在不同的凝集态中,由顺式回复到反式构型的速率明显不同.     

侧链型偶氮聚电解质自组装和膜结构研究

研究了4种侧链型偶氮聚电解质的自组装过程及其对自组装膜结构的影响.用聚电解质上的偶氮基团作为“探针”,研究了自组装过程中出现的生色团取向、解吸附和非线性增长等现象.这些侧链型偶氮聚电解质均具有较好的自组装性,但其自组装行为有很大差异.在不同的pH条件下,聚电解质的电离程度不同,导致吸附过程和自组装膜结构亦明显不同.自组装膜的增长和结构取决于体系中吸附和解吸的平衡.偶氮生色团端基的亲水或疏水性对自组装膜的增长有明显的影响.偶氮聚电解质自组装过程不同阶段出现的非线性增长现象,分别反映了基底、溶液性质和聚电解质结构等因素的影响.     

新型支化侧链偶氮聚电解质的合成与性能研究

通过后重氮偶合的方法合成了一种含支化侧链偶氮苯生色团的聚电解质 (PBANT AC) .用IR、NMR、DSC、UV和元素分析等手段对聚合物的结构和性能进行了表征 .研究发现 ,在不同比例的水和四氢呋喃混合溶剂中PBANT AC的紫外 可见光光谱有很大的差别 .这种差别反映了PBANT AC分子中的偶氮苯生色团的不同聚集状态 .通过静电吸附逐层自组装的方法将PBANT AC分子组装成多层膜 .在 488nm的偏振Ar+ 激光的照射下 ,聚合物薄膜中的偶氮苯生色团可发生光致取向 ,取向有序度约 0 0 5 .偶氮苯生色团的顺反异构化反应使H 聚集体在光照后发生解聚集     

端羧基芳脂型超支化聚酯自组装性能的研究

利用聚电解质逐层浸渍 ( layer- by- layer dipping)法制备自组装膜是最近发展起来的进行表面改性的新方法[1～ 3] .一方面 ,从理论上来说 ,只要是带电荷的聚合物都可以利用该技术制备具有优异性能的自组装膜 ;另一方面 ,还可以通过调节溶液的 p H值和离子强度等控制阴阳离子的组装过程 ,从而控制自组装膜的内部结构和表面形态 ,为在纳米级范围内设计和控制聚合物聚集态内部结构提供了可能性 .近年来 ,具有高度支化结构的超支化分子由于具有独特的物理和化学性能而受到了广泛的关注 [4 ,5] ,但以聚电解质逐层浸渍法制备超支化分子自组装膜…     

一种具有识别运输钠离子的离子通道膜的制备

以三氯甲烷为溶剂,用3-异氰酸基丙基三乙氧基硅烷和对氨基苯酚合成得到一种自组装杂化材料——3-(脲基酚基)丙基三乙氧基硅烷.采用FTIR、XPRD分析方法对该化合物的结构以及晶体形态进行了表征.利用旋涂法和共混法分别制备离子通道膜,采用ATR-FTIR和SEM分析手段表征膜的化学结构和形态结构,并通过自制的膜运输实验装置测定膜的传输性能并提出了相应的传输机理.实验结果表明,两种方式所得的离子通道膜表面是致密无孔的,致密层厚度为8～10μm左右;采用共混法制得的离子通道膜的传输速度较旋涂法快.离子通道是杂化材料通过分子自组装形成的,该通道可以识别并运输Na+.     

支化侧链偶氮聚电解质的光致二向色性和表面起伏光栅

通过后重氮偶合的方法合成了两种含支化侧链偶氮苯生色团的聚电解质PBANT AC和PBACT AC .用红外光谱、氢核磁共振谱、紫外 可见光光谱、热分析和元素分析等手段对聚合物的结构和性能进行了表征 .在 4 88nm的偏振Ar+ 激光的照射下 ,聚合物薄膜中的偶氮苯生色团可发生光致取向 ,取向有序度分别为 0 12和 0 0 9.在干涉偏振激光束的照射下 ,两种聚合物旋涂膜表面均形成了规则的正弦表面起伏光栅 ,其起伏深度分别为 4 0nm和 80nm左右 .用氦氖激光实时检测 ,测定了两种旋涂膜表面起伏光栅的一级衍射效率随光照时间的变化关系 .     

光学活性偶氮苯自组装膜的制备及其蛋白吸附行为

研究了在紫外光作用下, 牛血清白蛋白(BSA)在偶氮苯自组装膜上光控可逆的吸附行为. 首先合成羧基偶氮苯衍生物, 并在金膜表面制备偶氮苯自组装膜, 采用紫外吸收光谱(UV)、原子力显微镜(AFM)观察偶氮苯衍生物的光学顺反异构现象以及偶氮苯自组装膜表面形貌的变化. 同时利用等离子体表面谐振仪(SPR)考察偶氮苯光学异构对牛血清白蛋白(BSA)在自组装膜表面上的吸附行为的影响. 结果表明, BSA在偶氮苯自组装膜表面的吸附作用主要来自于BSA分子与自组装膜之间的静电作用及亲疏水作用. 在紫外光作用下, 偶氮苯自组装膜可以实现光控可逆的牛血清白蛋白分子吸附行为.     

Molecular dynamics simulations of multilayer polyelectrolyte films: effect of electrostatic and short-range interactions

The effect of the strength of electrostatic and short-range interactions on the multilayer assembly of oppositely charged polyelectrolytes at a charged substrate was studied by molecular dynamics simulations. The multilayer buildup was achieved through sequential adsorption of charged polymers in a layer-by-layer fashion from dilute polyelectrolyte solutions. The strong electrostatic attraction between oppositely charged polyelectrolytes at each deposition step is a driving force behind the multilayer growth. Our simulations have shown that a charge reversal after each deposition step is critical for steady multilayer growth and that there is a linear increase in polymer surface coverage after the first few deposition steps. Furthermore, there is substantial intermixing between chains adsorbed during different deposition steps. We show that the polymer surface coverage and multilayer structure are each strongly influenced by the strength of electrostatic and short-range interactions.     

Molecular dynamics simulations of layer-by-layer assembly of polyelectrolytes at charged surfaces: effects of chain degree of polymerization and fraction of charged monomers

We performed molecular dynamics simulations of the electrostatic assembly of multilayers of flexible polyelectrolytes at a charged surface. The multilayer build-up was achieved through sequential adsorption of oppositely charged polymers in a layer-by-layer fashion from dilute polyelectrolyte solutions. The steady-state multilayer growth proceeds through a charge reversal of the adsorbed polymeric film which leads to a linear increase in the polymer surface coverage after completion of the first few deposition steps. Moreover, substantial intermixing between chains adsorbed during different deposition steps is observed. This intermixing is consistent with the observed requirement for several deposition steps to transpire for completion of a single layer. However, despite chain intermixing, there are almost perfect periodic oscillations of the density difference between monomers belonging to positively and negatively charged macromolecules in the adsorbed film. Weakly charged chains show higher polymer surface coverage than strongly charged ones.     

Preparation of azo polyelectrolyte self-assembled multilayers by using N,N-dimethylformamide/H2O mixtures as solvents

N,N-Dimethylformamide (DMF)/H₂O mixtures were used as solvents to fabricate azo polyelectrolyte (PEAPH)/poly(diallyldimethyl ammonium chloride)(PDAC) self-assembled multilayers with the layer-by-layer electrostatic adsorption technique. PEAPH is a copolymer of acrylic acid and azobenzene-containing acrylate. The effect of the ratio of DMF to water on the multilayer growth, structure and surface morphology was studied in some details. Results show that DMF/H₂O mixtures are proper media for PEAPH/PDAC multilayer fabrication. The ratio of DMF to water in the mixture has significant influence on the multilayer structure and surface morphology. With the increase of DMF content, the multilayer thickness has a better linear growth relationship with the bilayer number, and the multilayer surface becomes smoother. Moreover, azo chromophores show less H-aggregation when the multilayers are fabricated from DMF/H₂O mixtures with higher DMF contents. These studies demonstrate that using organic solvent and water mixtures is an effective way to control the multilayer construction by adjusting the media properties. This method can be applied to multilayer fabrication of other water-insoluble polyelectrolytes. __________ Translated from Acta Polymerica Sinica, 2005, (4) (in Chinese)     

Facile method for the fabrication of robust polyelectrolyte multilayers by post-photo-cross-linking of azido groups

In this letter, we have developed a facile method to enhance the stability of polyelectrolyte multilayers. We fabricate conventional polyelectrolyte multilayers of PAH/PAA through electrostatic layer-by-layer (LbL) assembly and then postinfiltrate photosensitive cross-linking agent 4,4'-diazostilbene-2,2'-disulfonic acid disodium salt into the LbL films. After cross-linking by UV irradiation, the stability of the photo-cross-linked multilayer is highly improved as evidenced by the lack of dissolution under ultrasonication in saturated SDS aqueous solutions for 10 min. Moreover, by taking advantage of the different stability of the LbL film before and after UV irradiation, a patterned surface can be achieved.     

Lateral mobility of polyelectrolyte chains in multilayers

In this work, the lateral mobility of polyelectrolyte multilayers was investigated by means of the fluorescence recovery after photobleaching (FRAP) technique, with special attention to the effect of relevant parameters during and after preparation. Different polyelectrolytes with respect to charge density, stiffness, and hydrophilicity were compared. From the experimental results emerged that the density of charged sites along the polymer is the most important parameter controlling the formation of polymer complexes. At higher charge density, more complexes are formed, and the diffusion coefficient decreases. It was observed that the intrinsic backbone stiffness reduces the interpenetration of polyelectrolyte layers and the formation of complexes promoting the lateral mobility. In addition, the lateral mobility increases with increasing ionic strength and with decreasing hydration shell of the added anion in the polyelectrolyte solution. The effect of heating or annealing in electrolyte solution after preparation was also investigated along with the embedding of the probing layer at controlled distances to the multilayer surface.     

The structure of self-assembled multilayers with polyoxometalate nanoclusters

Using electrostatic layer-by-layer self-assembly (ELSA), the formation of multilayers with polyelectrolytes and nanoscopic polyoxometalate (POM) clusters of different sizes and charges is investigated. The multilayers are characterized by UV-vis absorption spectroscopy, optical ellipsometry, cyclic voltammetry, and atomic force microscopy. In all cases, it is possible to find experimental conditions to achieve irreversible adsorption and regular multilayer deposition. Most importantly, the surface coverage is directly related to the total charge of the POM anion and can be controlled from submonolayer to multilayer coverage by adjusting the ionic strength of the dipping solutions. Imaging the interfaces after POM deposition by atomic force microscopy reveals a granular surface texture with nanometer-sized features. The average interfacial roughness amounts to approximately 1 nm. Cyclic voltammetry indicates that the electrochemical properties of the POM clusters are fully maintained in the polyelectrolyte matrix, which opens a route toward practical applications such as sensors or heterogeneous catalysts. Moreover, the permeability toward electrochemically active probe molecules can be tailored through the multilayer architecture and deposition conditions. Finally, we note that despite the low total charge and comparably small size of the discrete POM anions, the multilayers are remarkably stable. This work provides basic guidelines for the assembly of POM-containing ELSA multilayers and provides detailed insight into characteristic surface coverage, permeability, and electrochemical properties.     

Role of chain interpenetration in layer-by-layer deposition of polyelectrolytes

The effects of temperature, pH, and salt concentration on the layer-by-layer (LBL) deposition of sodium poly(styrene sulfonate) (PSS)/poly[2-(dimethylamino)ethyl methacrylate] (PDEM) were investigated by use of a quartz crystal microbalance with dissipation (QCM-D). At pH 4, the frequency change (Deltaf) gradually decreased to a constant, indicating that the polyelectrolyte complexes of the layer were not dissolved. As the layer number increased, the -Deltaf oscillatedly increased, indicating that the thickness of the multilayer increased. At the same time, the dissipation change (DeltaD) oscillatedly increased with the layer number, indicating the chain interpenetration or complexation that led to the alternative swelling-and-shrinking of the outermost layer. For the same layer number, as the temperature increased, the amplitude of DeltaD increased, indicating that the chain interpenetration increased. The thickness also increased with temperature. Further increasing the pH to 7 led to a thicker layer, reflected in the larger amplitude of DeltaD. At pH 10, the polyelectrolytes no longer formed multilayers on the surface because of the lack of electrostatic interactions. On the other hand, the addition of NaCl also led to a thickness increase. The amplitude in DeltaD increased with NaCl concentration, indicating that the chain interpenetration increased. Our experiments indicated that the LBL deposition of polyelectrolytes was dominated by the chain interpenetration. Also, the polyelectrolyte complexes in the layer can redissolve into solution from the surface at a high temperature or a high salt concentration.     

旋涂-逐层自组装制备光响应性聚丙烯酸酯类偶氮聚电解质多层膜

偶氮聚电解质的静电逐层自组装是实现偶氮聚合物功能性的重要手段,是制备诸如光存储材料、光开关材料和非线性光学材料等的新途径.因此,光响应性偶氮聚电解质的静电逐层自组装已引起了人们的广泛关注.静电逐层自组装通常在水溶液中进行,即通过基材在在水溶液中的交替浸渍和逐层