分子复合材料研究进展(二)

６　分子复合材料的微观结构与性能目前分子复合材料多采用溶液共混法制备。研究表明［２，３］，三元共混物均相溶液的浓度、增强相分子，树脂基体和组份之间的相容性及加工成型条件等都对ＭＣ的微观相结构和力学性能影响很大。当共混物溶液浓度Ｃ＜＜Ｃｃｒ时，刚棒状分子（链段）之间无相互作用力，均相溶液呈光学各向同性，其溶液粘度（η）符合牛顿流体定律；此时体系为相容均相共混物；在Ｃ＜＜Ｃｃｒ时，刚棒状分子（链段）增强相与热塑性树脂基体的分子（链段）之间存在着相互作用力，溶液粘度（η）表现为非牛顿流体行为，但此时溶…     

邻位取代基对芳—脂族共聚酰胺热致液晶性能的影响

通过芳香二酰氯邻位取代基和芳香二元胺邻位取代基对所生成的大分子链的酰胺基的空间阻碍作用和脂肪族二胺与芳香族二胺的适宜配合，使大分子链的刚性和在分子链之间由酰胺基团所形成的氢键减弱，从而降低了熔融温度，达到了主链型热致液晶聚酰胺链组成设计的目的。‘     

PPy／SiO2纳米复合材料的合成与导电性能

以乙醚反应介质，用化学方法合成了聚吡咯纳米复合材料，利用红外光谱，四探针技术和透射镜表征了这些材料的组成，结构和导电性能，结果表明，载流子在ＰＰｙ分子链之间和ＰＰｙ聚集体之间有的传导性。     

基于β-环糊精自组装的氧化还原敏感超分子凝胶

分别合成了多酸EMPOL-1016分子链末端携带β-环糊精的主体分子(EM-βCD)和聚乙烯亚胺(600)分子链末端携带二茂铁的客体分子(PEI-Fc),并用核磁共振对PEI-Fc和EM-βCD的结构和组成进行了表征。研究表明,PEI-Fc和EM-βCD由于β-CD基团与Fc基团之间的主客体包合作用自组装形成超分子凝胶。由于β-CD-Fc之间的包结具有氧化还原性,PEI-Fc/EM-βCD凝胶可在氧化剂存在时呈溶胶状态,被还原时重新形成凝胶。     

自组装囊泡的结构与单分子膜的性质

研究了具有不同主链分子量和侧链长度的N，N-双烷基化壳聚糖单分子膜的性质．结果表明，主链分子量越大，所形成的N，N-双烷基壳聚糖单分子膜的结构越紧密．在主链分子量相同的条件下，N，N-双烷基壳聚糖单分子膜的致密度随着侧链长度的增大而增大，表明N，N-双烷基化壳聚糖分子间的缠结嵌套和疏水相互作用力的增大．比较N，N-双烷基化壳聚糖单分子膜与相应自组装囊泡的性质发现，囊泡的药物平衡释放率随着其相应材料单分子膜压缩模量的增大而减小，呈现出一定的线性关系．单分子膜压缩模量的大小反映囊泡膜结构的紧密程度．     

分子复合材料的研究进展

分子复合材料是指刚性高分子链(段)聚合物与柔性链聚合物(树脂)共混，刚性链高分子聚合物作为增强相在接近分子水平上均匀分散在柔性链(段)树脂基体中，达到最佳分子增强效应，形成高强度、高模量的复合材料。制备分子复合材料的关键在于溶混性。文中重点讨论了分子复合材料的制备方法与改进方法，简要介绍了分子复合材料的分类、特点及组成。     

聚乙烯醇和聚丙烯酸均聚物的自组装形貌

利用聚乙烯醇分子链上羟基与聚丙烯酸分子链上羧基之间的氢键相互作用,在水溶液中,根据羟基和羧基摩尔比的不同,形成了不同的组装结构。当羧基与羟基的摩尔比在10%~25%之间时,可以获得较为丰富的自组装结构。通过向溶液中添加5%~30%的甲醇,可以获得稳定的球形、棒状和网状纳米结构。动态光散射和透射电镜测试验证了聚集体的形成。通过分析聚合物链的不同氢键复合形式以及Zeta电位结果,提出了聚集体是以聚乙烯醇(PVA)/聚丙烯酸(PAA)复合链段为核,PVA链段为壳的结构。     

原子力显微镜探针针尖修饰的研究进展

介绍了当前几种AFM探针针尖修饰技术,以及它们在高分子材料、生物材料、微观摩擦学、粘附力、纳米级电化学、碳纳米管及纳米加工方面的研究进展。AFM探针针尖修饰的目的主要是:提高扫描图像分辨率,其分辨率可达纳米或亚纳米级别;用力曲线探究特定基团间的相互作用,定量分析端基与端基之间、分子链与分子链之间及端基与分子链之间的相互作用力,避免针尖对生物样品表面的损坏;对分子材料结构进行修饰,特别是在生物细胞、DNA分子链上及分子识别;避免Si或Si3N4针尖与表面硬度较大的样品直接接触,延长探针针尖的使用寿命。在研究天然橡胶硫化的作用机理时,可以用针尖修饰技术来模拟这个过程,探究天然橡胶分子链与单个硫原子的相互作用方式与作用力。通过电化学接枝聚合把高分子接枝在AFM针尖上,为研究单链的弹性力、引起构象转变的力、相互作用的双分子的分离力及特定的官能团的相互作用提供了许多可能性。分析了影响AFM探针针尖修饰的因素,结合材料领域方面的发展,对针尖修饰技术的发展及应用前景做了分析和预测。     

长短链醇混合单分子膜抑制水分蒸发的研究

以长链脂肪醇作为水分蒸发抑制剂，探讨了短链醇的引入、长短链醇的复配比例、环境温度等因素对分子膜抑制水分蒸发效果的影响。研究结果表明：与长链醇相比，将长短链醇复配可大幅度提升分子膜抑制水分蒸发的效果。其中，十六醇与正丁醇的复配效果最好，在温度为25℃，膜表面浓度为8．0×10^-2／m^2，复配比例为3：1时，抑制率最高可达66．7％。并且，混合单分子膜具有更好的抗温度干扰能力。分子膜的APM图像显示，长短链醇复配能形成比长链醇更为凝聚的分子膜，产生更为理想的抑制水分蒸发效果。     

自组装C60分子膜的微观摩擦行为

利用端基带－NH2的氨基酸自组装单分子膜与C60烯键反应形成共价键制成C60自组装膜，用原子力显微镜（AFM）研究了膜的微观摩擦学性能，结果表明，长链羟酸／C60分子膜的摩擦学性能优于短链羧酸分子膜；羧酸／C60分子膜的碳链中极性基团如羧基的存在，可以提高膜的平整度，改善膜的摩擦学性能。     

聚吡咯/聚多巴胺的电化学合成及其对铝合金耐蚀性的影响

为了提高铝合金有机涂层的耐蚀性,通过电化学方法在7075铝合金表面制备了海岛结构的聚吡咯（PPy）/聚多巴胺（PDA）复合涂层,利用FE-SEM、原子力显微镜、FTIR分析了PPy/PDA涂层的表面形貌、表面粗糙度和化学成分,并通过交流阻抗图谱分析了涂层的阻抗特性,通过极化曲线分析了具有PPy/PDA涂层的铝合金的极化电压和极化电流,研究其耐蚀特性。结果显示,通过一步法电化学聚合方法,吡咯和多巴胺在铝合金表面同时发生电化学聚合,生成PPy/PDA复合涂层,PPy/PDA涂层具有海岛结构,纯PPy和PPy/PDA涂层的粗糙度分别是（74.582±7.227）nm和（73.740±7.811）nm。交流阻抗和极化曲线说明PPy/PDA涂层相比于纯PPy涂层具有更大的阻抗力,PPy/PDA涂层的腐蚀电流和腐蚀电压分别是4.1825×10-6 Acm-2和-0.6919 V,相对于纯PPy（腐蚀电流和腐蚀电压分别是7.618×10-6 Acm-2和-0.7403 V）具有更好的防腐特性。      

Highly aligned ultrahigh density arrays of conducting polymer nanorods using block copolymer templates

Ultrahigh density arrays of conducting polypyrrole (PPy) nanorods are fabricated directly on the indium-tin oxide coated glass by an electropolymerization within a porous diblock copolymer template. The nanorods are shown to have conductivity much higher than thin PPy films, due to the high degree of chain orientation, even though the separation distance for two neighboring PPy main chains is as small as 0.37 nm. The ultrahigh density arrays of conducting polymer nanorods have potential applications as sensor materials, nanoactuators, and organic photovoltaic devices.     

Polypyrrole colloids—assisted proton transport in hydrated polyacrylic acid matrix

This paper reports an investigation into the rheological behavior of aqueous suspension systems consisting of colloidal polypyrrole (PPy) particles and polyacrylic acid (PAA). We have observed a strong interaction between PPy colloids and PAA chains in an aqueous medium. Based on this observation, a new polymer composite was prepared, in which PPy colloidal particles were uniformly distributed in a semi-interpenetrating network (semi-IPN) consisting of linear PAA (M.W.=2000) in a cross-linked polymer [poly(acrylamide-methylenebisacrylamide) PAAM-MBAM]. The weight ratio of PPy in the composites was varied in the range of 0.2%–2.3%, and as a result of the low PPy content, the composites are electrically non-conductive in the dry state. However, they become electrically conductive when hydrated. There is a percolation threshold of water content with respect to the electrical resistivity. The semi-IPN composites containing PPy appear to have a lower percolation threshold than the blank semi-IPN composite. For example, as the water content increases from 14 to 15 wt% the resistivity of semi-IPN embracing 0.8% PPy reduces 10 times, while that of the blank semi-IPN reduces only 1.3 times. The difference in electrical resistivity may be attributed to the enhancement of proton transport by PPy colloids. This enhancement is probably due to the fact that PPy possesses a weak Brønsted basicity as well as a rigid conjugated structure. In other words, nitrogen atoms of PPy may coordinate with protons not too strongly and allow the protons to transport along the planar conjugated structure of PPy, thus contributing to the proton conductivity.     

Radiolytic synthesis of conducting polypyrrole/carbon nanotube composites

Conducting polypyrrole (PPy)/multi-wall carbon nanotube (MWNT) composites have been synthesized by the in situ gamma radiation-induced chemical polymerization method at room temperature. The resulting cable-like morphology of the composite (PPy–MWNT) structures was characterized by elemental analysis, Fourier transform infrared, field-emission scanning electron microscope, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and transmission electron microscope. The standard four-point probe method was utilized for measuring the conductivity of the samples. We observed no significant chemical reaction between the polymer and carbon nanotube, which only showed that polypyrrole chains are tightly coated on to MWNT. The physical properties of the composites (PPy–MWNT) were measured and showed that the MWNT were modified by conducting polypyrrole with various properties enhanced.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

Preparation of conductive polypyrrole-palladium composite nanospheres by inverse microemulsion polymerization

Conductive polypyrrole-palladium (PPy-Pd) composite nanospheres of about 50 nm in diameter, containing dispersed Pd metal nanoparticles of about 2-4 nm in size, were prepared in a 1-step oxidative polymerization of pyrrole by Pd(NO3)2. Pyrrole was oxidized by Pd(NO3)2 in an inverse microemulsion polymerization system, yielding PPy nanospheres and elemental Pd nanoparticles simultaneously. Palladium nanoparticles were uniformly dispersed in the nanospheres of PPy chains. The latter also exhibited an enhanced effective conjugation. The chemical composition of the PPy-Pd composite nanospheres was characterized by X-ray photoelectron spectroscopy and FTIR spectroscopy. The crystalline structure of the Pd nanoparticles was deduced from X-ray diffraction patterns. The morphology of the composites was revealed by scanning and transmission electron microscopy.     

Synthesis,characterization and weight percent effect on humidity sensing properties of Polypyrrole/AlCeO3 (PPy/ACO) nanocomposites

Polypyrrole (PPy)/aluminum cerium oxide (ACO) nanocomposites with different weight percentages of the ACO nanoparticles in the matrix of PPy have been synthesized successfully. The addition of fillers in the conducting polymer makes significant changes in their electrical, chemical, mechanical and gas sensing properties. The exact amount of filler is one of the essential parameters to get the desired properties in the host polymer. So, the optimization of the percent weight of filler in the host conducting polymer is very much crucial. The structural and morphological studies were done by XRD, FTIR, SEM, and TEM. These experimental studies reveal that nanoparticles of Aluminum cerium oxide are dispersed uniformly in the PPy chains. The humidity sensing properties for different weight percent of nanocomposites were studied by using impedance analyzer in the frequency range from 100?Hz to 5?MHz and at relative humidity (% RH) variation from 30% RH to 90% RH. The graphs of impedance versus frequency for all nanocomposites showed a slightly linear dependence at all the frequencies over the entire humidity range. The complex impedance (cole-cole) graphs and the corresponding equivalent circuits were studied to understand the conduction phenomenon in nanocomposites. The conduction in pure PPy shows the contribution from grain and grain boundaries while all the nanocomposites show contribution only from grains. The lower weight percent nanocomposites exhibit better response compared to higher weight percent.     

Enhancement of conductivity stability of polypyrrole films modified by valence copper and polyethylene oxide in an oxygen atmosphere

The degradations of polypyrrole (PPy)-based films in conductivity are examined in an oxygen atmosphere for 50 days. The results reveal that polymerization potential, solvents used in polymerization, modification of PPy with valence Cu, and introduction of polyethylene oxide (PEO) into PPy influence the conductivities of PPy films and their corresponding stabilities significantly. Pure PPy, prepared in water at an over-oxidized potential, shows a serious decrease in conductivity. However, valence Cu-modified PPy and PEO-modified PPy, resulting in an electron transfer from Cu to N⁺ of PPy and a more compact, dense surface and hydrogen bonds forming, respectively, behave more stable. The changes of surface mean roughness before and after aging are quantitatively measured via atomic force microscopy (AFM) analysis. Meanwhile, SERS experiments provide a deeper insight into the aging mechanism of PPy in conductivity.     

In situ growth of Prussian blue nanocubes on polypyrrole nanoparticles: facile synthesis,characterization and their application as fiber optic gas sensor

Polypyrrole (PPy) and polypyrrole/Prussian blue (PPy–PB) nanocomposite-based fiber optic gas sensors are developed for gas sensing application. Prussian blue (PB) nanocubes are successfully grown on polypyrrole (PPy) nanoparticles by in situ oxidative polymerization method to obtain PPy–PB nanocomposite. PPy and PPy–PB are evaluated based on structural, morphological and electrical properties. The characteristic peaks present in the FTIR spectra of pure PPy and PB nanoparticles are also present in the FTIR spectrum of PPy–PB nanocomposite with small shifts in the absorption maximum. The XRD pattern reveals the semicrystalline structure of PPy–PB nanocomposite with an average crystallite size of 22 nm, and the morphology (FESEM) shows the formation of PB nanocubes over PPy matrix. AC conductivity measurements show slight improvement in the conductivity value of PPy–PB in comparison with PPy. Dielectric studies in the frequency range of 50 Hz–5 MHz reveal that PPy–PB nanocomposite is a high-k dielectric material. At 50 Hz, PPy–PB exhibits high dielectric constants of 1149 and 766 with low dielectric loss values of 9.9 and 4.6 at 150 and 120 °C, respectively. Further, their application as fiber optic gas sensors in sensing various gases is studied using fiber optic technique. The spectral response is studied for various concentrations (0–500 ppm) of ammonia, acetone and ethanol gases at room temperature. The study shows that the spectral intensity increases linearly with different concentrations of all gases. The clad-modified fiber optic sensor with PPy–PB nanocomposite exhibits enhanced sensitivity for ethanol than clad-modified fiber optic sensor with PPy nanoparticles. TGA studies reveal the high thermal stability of PPy–PB nanocomposite. Hence, PPy–PB-based fiber optic sensors can be used to sense toxic ethanol vapor not only at room temperature but also in a composite environment where a temperature variation is expected.     

气液相聚合制备蒙脱土/聚吡咯的结构特征及其导电性能

以FeCl₃为氧化剂,与钠基蒙脱土(MMT)以不同比例进行离子交换后所得悬浮液与吡咯(Py)单体进行气液相聚合,制备出蒙脱土/聚吡咯(MMT/PPy)复合材料。XRD、FTIR和SEM分析表明,Py单体在MMT的片层间发生了聚合反应,MMT的层间距随PPy含量增加不断变大。MMT/PPy复合材料呈现出 MMT和PPy的红外特征吸收峰,但某些吸收峰出现蓝移。SEM 观察显示MMT/PPy呈片状形态特征。当其中的MMT去除后,PPy仍为片状结构,与纯 PPy的球粒形貌不同。电导率测试表明,MMT/PPy复合材料的电导率随PPy含量增加而提高,至40.9 wt% PPy含量时,MMT/PPy的电导率已达到PPy 的电导率水平(10-1S/cm),含54.3 wt% PPy的MMT/PPy电导率甚至略高于PPy。