Synthesis and characterization of conductive polypyrrole/multi-walled carbon nanotubes composites with improved solubility and conductivity

High conductivity and solubility of polypyrrole (PPy)/multi-walled carbon nanotubes (MWCNT) composites has been successfully synthesized by in situ chemical oxidation polymerization using various concentrations of cationic polyelectrolyte poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate (APS). Raman spectroscopy, FTIR, EPR, FESEM and HRTEM were used to characterize their structure and morphology. These images of FESEM and HRTEM showed that the fabricated PPy/MWCNT composites are one-dimensional core-shell structures with the average thickness of the PPy/MWCNT composites without PSS is about 250 nm and considerably decreases to 100–150 nm by adding the PSS content. The results of Raman spectrum, FTIR and UV–Vis indicate the synthesized PPy/MWCNT composites are in the doped state. The conductivities of PPy/MWCNT composites synthesized with the weight ratio of PSS/pyrrole monomer at 0.5 are about two times of magnitude higher than that of PPy/MWCNT composites without PSS. These results are perhaps due to the part of cationic electrolyte served as a dopant can be incorporated to the PPy structure to improve the conductivity of fabricated PPy/MWCNT composites.     

Consecutively spin-assembled layered nanoarchitectures of poly(sodium 4-styrene sulfonate) and poly(allylamine hydrochloride)

The recently established spin-coating electrostatic self-assembly (SCESA) technique has been shown to facilitate not only the rapid fabrication of polyelectrolyte multilayer assemblies, but also allow each layer to be easily controlled on a monomolecular scale by minimizing the film thickness across a substrate surface. In this paper, the influence of polyelectrolyte concentration on the amount and thickness of spin-deposited polymer films has been examined for a multilayer system of poly(allyamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), when the washing steps employed for removing weakly bound polyelectrolytes on a resultant film on a substrate are excluded from the standard fabrication procedure of the SCESA method. The thickness of the spin-deposited PAH/PSS bilayer increased linearly for the PSS concentrations in the range from 1 to 10 mM with PAH constant at 1 mM, which demonstrates the uniform deposition of each layer material onto the thin film. The thickness of PAH/PSS bilayers increased from 1.43 ± 0.06 to 3.37 ± 0.08 nm as the PSS concentration increased from 1 to 10 mM, while the PAH concentration was kept constant at 1 mM. The multilayer films were found to be stable in a good solvent (H₂O) for at least 30 h, without any noticeable loss of the adsorbed layer component of the polyelectrolyte. This improvement to the SCESA method (exclusion of washing steps) provides a convenient way to create multilayer heterostructures with the thickness of each layer being easily adjusted.     

From hollow shells to artificial cells: biointerface engineering on polyelectrolyte capsules

Biomimetic composites can be fabricated by coating hollow polyelectrolyte capsules with biological interfaces such as a phospholipid membrane and proteins. Polyelectrolyte capsules have been templated applying the Layer-by-Layer technique of polyelectrolyte assembled on decomposable cores, which are destroyed after the assembly of the polyelectrolyte multilayer. Phospholipid vesicles of 200-300 nm size are spreaded on the capsule wall forming a continuous lipid membrane. Further functionalisation of the outer capsule wall can be achieved with fused virions and recrystallised S-layers. Compartimentation of the capsule interior with lipid vesicles has been possible by using a solvent exchange method. The functionalisation of the outer capsule surface with biomolecules, together with the creation of internal compartments in the capsule, open new nanobiotechnological challenges towards the fabrication of artificial cells.     

Liposome-based nanocapsules

Here we present three different types of mechanically stable nanometer-sized hollow capsules. The common point of the currently developed systems in our laboratory is that they are liposome based. Biomolecules can be used to functionalize lipid vesicles to create a new type of intelligent material. For example, insertion of membrane channels into the capsule wall can modify the permeability. Covalent binding of antibodies allows targeting of the capsule to specific sites. Liposomes loaded with enzymes may provide an optimal environment for them with respect to the maximal turnover and may stabilize the enzyme. However, the main drawback of liposomes is their instability in biological media as well as their sensitivity to many external parameters such as temperature or osmotic pressure. To increase their stability we follow different strategies: 1) polymerize a two-dimensional network in the hydrophobic core of the membrane; 2) coat the liposome with a polyelectrolyte shell; or 3) add surface active polymers to form mixed vesicular structures.     

静电自组装制备CdTe量子点纳米薄膜

以巯基丙酸为稳定剂, 在水相中合成了表面带负电荷、具有良好的分散性、平均粒径为5nm的CdTe量子点. 通过CdTe量子点与阳离子聚电解质聚二烯丙基二甲基氯化铵(PDDA)和阴离子聚电解质聚苯乙烯磺酸钠(PSS)之间的静电相互作用, 在石英基片表面通过层层静电自组装方法制备了多层CdTe量子点纳米薄膜. 以荧光分光光度计、UV-Vis、XPS、AFM等测试手段对所得的CdTe量子点纳米薄膜进行了表征. 研究结果表明, CdTe量子点自组装多层薄膜的UV-Vis吸光度与组装层数基本呈线性关系, 薄膜成膜质量良好. 自组装薄膜基本上规整并均匀地覆盖在石英基底表面, 但薄膜中存在部分CdTe量子点聚集现象. 通过在相邻的两层CdTe量子点之间引入基本结构单元为PDDA/PSS/PDDA的聚电解质复合层, 可有效提高CdTe量子点纳米薄膜的成膜质量. 所得的CdTe量子点纳米薄膜具有良好的荧光光致发光性.     

Redox-controlled molecular permeability of composite-wall microcapsules

Many smart materials in bioengineering, nanotechnology and medicine allow the storage and release of encapsulated drugs on demand at a specific location by an external stimulus. Owing to their versatility in material selection, polyelectrolyte multilayers are very promising systems in the development of microencapsulation technologies with permeation control governed by variations in the environmental conditions. Here, organometallic polyelectrolyte multilayer capsules, composed of polyanions and polycations of poly(ferrocenylsilane) (PFS), are introduced. Their preparation involved layer-by-layer self-assembly onto colloidal templates followed by core removal. PFS polyelectrolytes feature redox-active ferrocene units in the main chain. Incorporation of PFS into the capsule walls allowed us to explore the effects of a new stimulus, that is, changing the redox state, on capsule wall permeability. The permeability of these capsules could be sensitively tuned via chemical oxidation, resulting in a fast capsule expansion accompanied by a drastic permeability increase in response to a very small trigger. The substantial swelling could be suppressed by the application of an additional coating bearing common redox-inert species of poly(styrene sulfonate) (PSS(-)) and poly(allylamine hydrochloride) (PAH(+)) on the outer wall of the capsules. Hence, we obtained a unique capsule system with redox-controlled permeability and swellability with a high application potential in materials as well as in bioscience.     

Layer-by-Layer assembly of TiO2 nanoparticles for stable hydrophilic biocompatible coatings

Stable, super-hydrophilic (water contact angle approximately equal to 0 degrees) titanium dioxide nanoparticle thin films have been obtained on substrates with different initial wettability such as glass, poly(methyl methacrylate) and poly(dimethyl siloxane) using layer-by-layer nano-assembly method. Titanium dioxide nanoparticles were alternated with poly(styrene sulfonate) to form films of thickness ranging from 11 nm to 220 nm. The hydrophilicity of these thin films increases with increasing number of deposited PSS/TiO2 bilayers. It was found that 2, 5 and 20 layers were needed to form super-hydrophilic TiO2 coating on glass, PMMA and PDMS respectively. Oxygen plasma treatment of substrate surfaces enhanced the formation of homogeneous TiO2 films and accelerated the formation of hydrophilic layers. Super-hydrophilicity has been shown to be unique to PSS/TiO2 films as compared with other polyelectrolyte/nanoparticle layers, and UV irradiation may restore hydrophilicity even after months of storing of the samples. Biocompatibility of TiO2 nanoparticle films has been demonstrated by the successful cell culture of human dermal fibroblast.     

以MnCO3为模板的聚电解质胶囊的制备

通过沉淀反应制备MnCO3，以乙醇为添加剂成功制备出分散性好的、具有所需尺寸和很窄的粒径分布的球形MnCO3微粒。采用MnCO3粒子为模板吸附相反电荷聚电解质再除去核来制备纯净中空聚电解质胶囊。对组装到MnCO3上制备出来的中空聚电解质胶囊作了研究。结果表明：这种胶囊代表了仅含有所需物质的微米尺度的独立式的聚电解质膜。粒子表面结构决定了所制备的胶囊的形态和胶囊壁厚度。     

Osmocapsules for Direct Measurement of Osmotic Strength

Monodisperse microcapsules with ultra‐thin membranes are microfluidically designed to be highly sensitive to osmotic pressure, thereby providing a tool for the direct measurement of the osmotic strength. To make such osmocapsules, water‐in‐oil‐in‐water double‐emulsion drops with ultra‐thin shells are prepared as templates through emulsification of core–sheath biphasic flow in a capillary microfluidic device. When photocurable monomers are used as the oil phase, the osmocapsules are prepared by in‐situ photopolymerization of the monomers, resulting in semipermeable membranes with a relatively large ratio of membrane thickness to capsule radius, approximately 0.02. These osmocapsules are buckled by the outward flux of water when they are subjected to a positive osmotic pressure difference above 125 kPa. By contrast, evaporation‐induced consolidation of middle‐phase containing polymers enables the production of osmocapsules with a small ratio of membrane thickness to capsule radius of approximately 0.002. Such an ultra‐thin membrane with semi‐permeability makes the osmocapsules highly sensitive to osmotic pressure; a positive pressure as small as 12.5 kPa induces buckling of the capsules. By employing a set of distinct osmocapsules confining aqueous solutions with different osmotic strengths, the osmotic strength of unknown solutions can be estimated through observation of the capsules that are selectively buckled. This approach provides the efficient measurement of the osmotic strength using only a very small volume of liquid, thereby providing a useful alternative to other measurement methods which use complex setups. In addition, in‐vivo measurement of the osmotic strength can be potentially accomplished by implanting these biocompatible osmocapsules into tissue, which is difficult to achieve using conventional methods.     

静电自组装制备复合磨粒及其 对铜的抛光特性研究

研究苯代三聚氰胺甲醛（BGF）微球与阳离子型聚电解质聚二烯丙基二甲基氯化铵（PDADMAC）、阴离子型聚电解质聚4－苯乙烯璜酸钠（PSS）之间的吸附特性,利用静电自组装技术改变和控制BGF微球的荷电特性,制备出不同形式的PEi BGF/SiO2复合磨粒,以Zeta电位、透射电子显微镜（TEM）和热重分析（TG）等手段对复合磨粒进行了表征,并利用这些复合磨粒制备了铜片抛光用的复合磨粒抛光液。抛光试验表明,吸附在聚合物微球表面和游离于抛光液中的SiO2磨粒在抛光中均起到材料去除作用。传统单一SiO2磨粒抛光液的铜材料去除率为264 nm/min,PE0 BGF/SiO2混合磨粒抛光液的铜材料去除率为348 nm/min,PE3 BGF/SiO2复合磨粒抛光液的铜材料去除率为476 nm/min。经上述3种抛光液抛光后的铜表面,在5 μm×5 μm范围内,表面粗糙度Ra从0.166 μm分别降至3.7 nm、2.6 nm和1.5 nm,峰谷值Rpv分别小于20 nm、14 nm和10 nm,复合磨粒抛光液对铜片有良好的抛光性能。     

Photoresponsive layer-by-layer ultrathin films prepared from a hyperbranched azobenzene-containing polymeric diazonium salt

In this work, a hyperbranched diazonium salt (HB-DAS), prepared through azo-coupling reaction of an AB₂ monomer (N, N-bis[2-(4-aminobenzoyloxy)ethyl]aniline), was used to prepare self-assembled multilayers and ultrathin films. Multilayer films were fabricated by dipping substrates in HB-DAS and other polyelectrolyte solutions alternately in a layer-by-layer (LBL) manner. It was somewhat surprising to observe that HB-DAS forms multilayer films with either a polyanion (poly(styrenesulfonate sodium salt), PSS) or a polycation (poly(diallyldimethylammonium chloride), PDAC) through alternate deposition in the solutions. Ultrathin films were formed in a sequential growth manner by dipping the substrates in the HB-DAS solution, washing with deionized water and drying repeatedly. In all the processes, the absorbance and thickness of the thin films linearly increase as the number of the dipping cycle increases. HB-DAS/PSS multilayer possesses an obviously larger bilayer thickness and lower density compared with the other two counterparts. The drying step after each deposition is necessary for the HB-DAS ultrathin film growth through the repeated dip-coating of HB-DAS. The multilayer and ultrathin films prepared by the above methods all show high resistance to erosion by organic solvents. The multilayers and ultrathin films exhibit photoinduced dichroism upon the irradiation of a polarized Ar⁺ laser beam.     

Fabrication of fluorescent hollow capsule with CdS–polyelectrolyte composite films

CdS–polyelectrolyte (CdS–PE) clusters were synthesized by using polyelectrolyte as the stabilizing agent in the aqueous solution. The blue shift of UV–Vis and Fluorescent spectra, the TEM images show the formation of nanoparticles within the polyelectrolyte chains. Using the normal polyelectrolyte hollow capsules as template, the CdS–PE clusters as functional layer materials, the uniform organic–inorganic hollow microspheres have been produced by layer-by-layer (LbL) self-assembly technology.     

Hydrogen-bonding layer protecting polyelectrolyte capsules and its mechanical property study with atomic force microscope

The hydrogen-bonding multilayered polyelectrolyte capsules with sizes around 6 microm were fabricated by layer-by-layer self-assembly method. The morphology of the obtained capsules was observed with Scanning Electron Microscope (SEM), Confocal Laser Scanning Microscope (CLSM) and Atomic Force Microscope (AFM), respectively. The elastic properties of the capsules were studied with AFM. The capsule was pressed by cantilever with different lengths, a glass bead glued at the end of the cantilever. The force curves were measured on the capsule in air. The Young's modulus of the capsule was obtained (E = 170 MPa for the loading). Results show that this model can predict the elastic deformation of the microcapsule. The accuracy of the elastic deformation of polymer capsule can be ensured using a cantilever of mediate stiffness. Our results show that the existence of the hydrogen-bonding layer makes the multilayered polyelectrolyte harder in comparison with the pure multilayered polyelectrolyte capsules.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

Femtomolar electrochemical detection of DNA hybridization using hollow polyelectrolyte shells bearing silver nanoparticles

The preparation, and use as electrochemical labels, of polyelectrolyte shells bearing Ag nanoparticles is described. Their potential for highly sensitive detection is demonstrated. The shells are prepared by layer-by-layer self-assembly around templates (500 nm diameter) which are then dissolved. The shells can be opened and closed by adjustment of solution pH, and this process is utilized to encapsulate Ag nanoparticles, chiefly by adsorption to the inner walls of the capsules. Based on absorbance, TEM and voltammetric measurements, the highest loading achieved is approximately 78 Ag particles per capsule. The Ag capsules are used via biotin-avidin binding as labels for the detection of DNA hybridization, following acid dissolution and then detection of the Ag (+) by ASV. A 30-mer sequence specific to Escherichia coli is measured at DNA-modified screen-printed electrodes with a detection limit of approximately 25 fM, which corresponds to the detection of 4.6 fg ( approximately 3 x 10 (5) molecules) in the 20 microL analyte sample. A 200 fM target containing a single mismatch gives a significantly (<74%) lower response than 200 fM of complementary target; 60 pM of noncomplementary target gives a negligible response.     

磁性石墨烯的制备初探

目的制备磁性石墨烯,实现其定向排列,为进一步制备性能良好的热界面材料提供定向导热相。方法采用聚合物包覆和层层组装技术,在石墨烯表面均匀包覆带负电荷的聚磺苯乙烯(PSS)聚电解质层,然后在静电力作用下包覆一层带正电荷的聚二烯丙基二甲基氯化铵(PDDA)聚电解质。最后,借助静电力使带负电荷的磁性Fe3O4纳米粒子在附着有PDDA层的石墨烯表面形成均匀的致密覆盖层,得到磁性石墨烯,并在外磁场作用下使磁性石墨烯进行定向排列。结果采用聚电解质层层组装技术可有效地对石墨烯进行磁性化处理;粉状石墨烯比片状石墨烯定向排列效果明显;以片状石墨烯为原材料的实验条件下,加入聚电解PSS、PDDA的量越多,磁性化效果更佳。结论通过聚电解质层层组装技术可有效地对石墨烯进行磁性化处理,并在磁场作用下实现定向排列。     

Multiwall carbon nanotube and poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) composite films for transistor and inverter devices

Highly conductive multiwalled carbon nanotube (MWNT)/Poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) films were prepared by spin coating a mixture solution. The solution was prepared by dispersing MWNT in the PEDOT:PSS solution in water using ultrasonication without any oxidation process. The effect of the MWNT loading in the solution on the film properties such as surface roughness, work function, surface energy, optical transparency, and conductivity was studied. The conductivity of MWNT/PEDOT:PSS composite film was increased with higher MWNT loading and the high conductivity of MWNT/PEDOT:PSS films enabled them to be used as a source/drain electrode in organic thin film transistor (OTFT). The pentacene TFT with MWNT/PEDOT:PSS S/D electrode showed much higher performance with mobility about 0.2 cm2/(V s) and on/off ratio about 5 × 10? compared to that with PEDOT:PSS S/D electrode (～0.05 cm2/(V s), 1 × 10?). The complementary inverters exhibited excellent characteristics, including high gain value of about 30.     

Efficiency enhancement of polymer solar cells with Ag nanoparticles incorporated into PEDOT:PSS layer

In this study, large-sized silver nanoparticles (Ag NPs) (average size: 80 nm) have been introduced into the anodic buffer poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer (thickness: about 55 nm) of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunction polymer solar cells. The results showed that the short-circuit current density can increase from 8.73 to 11.36 mA/cm², and power conversion efficiency increases from 2.28 to 2.65 % when 0.1 wt% Ag NPs was incorporated in PEDOT:PSS layer, corresponding to an efficiency improvement of 16.2 %. Absorption spectrums of the active layers indicate that large-sized Ag NPs have no clear contribution to optical absorption improvement. By measuring the conductivity of PEDOT:PSS films without and with Ag NPs and analyzing device structure of this polymer solar cell, it was founded that the improvements in power conversion efficiency was originated from higher conductivity of PEDOT:PSS layer incorporated with Ag NPs and the shorter routes for holes to travel to the anode.     

Approaches to quantifying and visualizing polyelectrolyte multilayer film formation on particles

Colloidal particles prepared by using the layer-by-layer technique are increasingly finding application in diagnostics, drug delivery, and sensing. Herein, we outline methods for applying three established techniques, confocal laser scanning microscopy (CLSM), flow cytometry, and differential interference contrast (DIC) microscopy, to characterize ultrathin films of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) assembled on silica particles. Both CLSM and flow cytometry require the use of fluorescently labeled polyelectrolytes (PEs). The film homogeneity can be assessed using CLSM, while flow cytometry allows analysis at unparalleled speed (thousands of particles per second) with unprecedented sensitivity (<0.5 fg of adsorbed polymer) of polydispersed particles of different size ( approximately 300 nm to tens of micrometers). Using CLSM and flow cytometry measurements, in conjunction with quartz crystal microgravimetry measurements on planar supports, allows quantification of PSS/PAH layer buildup on the particles. Furthermore, flow cytometry and DIC microscopy were used to unequivocally distinguish between silica-core PSS/PAH-shell particles and hollow PSS/PAH capsules obtained following core removal. The techniques outlined here are not limited to measuring PE deposition on solid particles but, in principle, are equally applicable to quantifying the adsorption of other materials (such as DNA, proteins, or nanoparticles) on a variety of particulate systems, including hollow capsules, emulsions, and cells.