Polypyrrole Nanowires Grown from Single Adsorbed Polyelectrolyte Molecules

Harnessing Smectic Ordering for Electric-Field-Driven Guided-Growth of Surface Topography in a Liquid Crystal Polymer

The guided-growth strategy has been widely explored and proved its efficacy in fabricating surface micro/nanostructures in a variety of systems. However, soft materials like polymers are much less investigated partly due to the lack of strong internal driving mechanisms. Herein, the possibility of utilizing liquid crystal (LC) ordering of smectic liquid crystal polymers (LCPs) to induce guided growth of surface topography during the formation of electrohydrodynamic (EHD) patterns is demonstrated. In a two-stage growth, regular stripes are first found to selectively emerge from the homogeneously aligned region of an initially flat LCP film, and then extend neatly along the normal direction of the boundary line between homogeneous and homeotropic alignments. The stripes can maintain their directions for quite a distance before deviating. Coupled with the advanced tools for controlling LC alignment, intricate surface topographies can be produced in LCP films starting from relatively simple designs. The regularity of grown pattern is determined by the LC ordering of the polymer material, and influenced by conditions of EHD growth. The proposed approach provides new opportunities to employ LCPs in optical and electrical applications.

Nanoarchitectonics for conductive polymers using solid and vapor phases

Conductive polymers have been extensively studied as functional organic materials due to their broad range of applications. Conductive polymers, such as polypyrrole, polythiophene, and their derivatives, are typically obtained as coatings and precipitates in the solution phase. Nanoarchitectonics for conductive polymers requires new methods including syntheses and morphology control. For example, nanoarchitectonics is achieved by liquid-phase syntheses with the assistance of templates, such as macromolecules and porous materials. This minireview summarizes the other new synthetic methods using the solid and vapor phases for nanoarchitectonics. In general, the monomers and related species are supplied from the solution phase. Our group has studied polymerization of heteroaromatic monomers using the solid and vapor phases. The surface and inside of solid crystals were used for the polymerization with the diffusion of the heteroaromatic monomer vapor. Our nanoarchitectonics affords to form homogeneous coatings, hierarchical structures, composites, and copolymers for energy-related applications. The concepts using solid and vapor phases can be applied to nanoarchitectonics for not only conductive polymers but also other polymers toward a variety of applications.

Nanoscaled surface patterning of conducting polymers

In continuing the steady development of integrated-circuit-related fabrication, the ability to pattern conducting polymers into smaller and smaller sizes in order to realize devices with enhanced performance or even wholly new properties begins to take a more prominent role in their advanced applications. This review summarizes the recent advances in top-down and bottom-up patterning of conducting polymers on surfaces with different approaches including direct writing, in-situ synthesis or assembly, etching, and nanoscratching. All of the latest emerging strategies have the potential to go beyond the current state of the art towards real progress in terms of high-precision positioning, high resolution, high throughout, higher stability, facile processing, and lower-cost production.

Facile synthesis of water-dispersible conducting polymer nanospheres

Water-dispersible polypyrrole nanospheres with diameters of less than 100 nm were synthesized in high yield without any templates, surfactants, or functional dopants by the introduction of 2,4-diaminodiphenylamine as an initiator into a reaction mixture of pyrrole monomer, oxidant, and acid. The initiator plays a critical role in tailoring the nanostructures of polypyrrole. 2,4-Diaminodiphenylamine interacts with acid to form cations, which combine with various anions to self-assemble resulting in different size nanomicelles. These nanomicelles, stabilized by initiator molecules, act as templates to encapsulate pyrrole and oxidant leading to the formation of nanospheres during polymerization. When smaller acids are used, smaller diameter sphere-like polypyrrole nanostructures are obtained. The as-synthesized polypyrrole nanospheres can then be used to fabricate highly conducting nitrogen-doped carbon nanospheres with controllable sizes of 50-220 nm with monodispersities up to 95% after pyrolysis. The size of the carbon nanospheres decreases by 20-30 nm due to carbonization when compared to the original polymer nanospheres. The molecular structures, morphologies, and electrical properties along with the formation mechanism of the polypyrrole and carbon nanospheres are discussed.

Organic supernanostructures self-assembled via solution process for explosive detection

Three different polymorphic crystalline structures, including microbelts and flowerlike supernanostructures, were obtained via a simple solution process by utilizing different solvents from an oligoarene derivative. Explosive chemosensors based on these self-assembled organic crystalline nanostructures were successfully fabricated. The differences in the structures on the microscopic level and in the film morphologies led to dramatic enhancements of the explosive detection speed. With the evolution of structures from the netted 1D microbelts to the flowerlike supernanostructures, the detection speed of the chemosensors for DNT and TNT was improved by more than 700 times. Our discovery demonstrates that the morphology control through self-assembly provides a new platform to utilize organic crystalline microstructures for chemosensors, optoelectronics, biosensors and bioelectronics, and so forth.

Human Serum Albumin−Mercurial Species Interactions

Binding of metal ions to the heteroatomic sites of proteins is undoubtedly fundamental to their observed physiological effects. In this paper, the interactions of inorganic mercury (Hg2+), methylmercury (MeHg+), ethylmercury (EtHg+), and phenylmercury (PhHg+) with human serum albumin (HSA) were studied from the electrophoretic behaviors, stoichiometry, thermodynamics, and kinetics by using a new hybrid technique, capillary electrophoresis on-line coupled with electrothermal atomic absorption spectrometry (CE-ETAAS), together with the consequent structural information from circular dichroism and Raman spectroscopy. The stoichiometry (mercurial species to HSA) for the interactions of Hg2+, MeHg+, EtHg+, and PhHg+ with HSA was found to be 6:1, 4:1, 4:1, and 3:1, respectively. Two types of binding sites in HSA were observed for the binding of mercurial species with the orders of magnitude of binding constants of 10(7) and 10(6) L mol-1, respectively, showing strong affinity of mercurial species for HSA. The interactions of mercurial species with both types of binding sites in HSA are exothermic and thermodynamically favorable and are both enthalpically and entropically driven. The binding of mercurial species to HSA follows the first-order kinetics for mercurial species and zero-order kinetics for HSA with the apparent activation energy of 57-59 kJ mol-1. Among the four mercurial species examined, only Hg2+ induces the secondary structure transition of HSA. Mercury-HSA adducts are formed mainly through metal-sulfur binding with participation of C=O and/or C-N groups of amino acid residues in HSA molecules. The present work represents the most comprehensive study on the interactions between various mercurial species with HSA and provides new evidence for and insights into the interactions of mercurial species with HSA for further understanding of the toxicological effects of mercurial species.

Facile Synthesis and Intrinsic Conductivity of Novel Pyrrole Copolymer Nanoparticles with Inherent Self-Stability

Intrinsically self-stabilized nanoparticles of a copolymer from 4-sulfonic diphenylamine (SD) and pyrrole (PY) were facilely synthesized in HCl solution at 10 degrees C by a chemically oxidative polymerization. The critical reaction parameters such as SD/PY ratio, polymerization time, and oxidant species were studied to significantly optimize the polymerization yield, size, conductivity, and solubility of the final copolymer particles. The molecular structure, size, size distribution, and morphology of the particles were analyzed by IR spectroscopy, laser particle-size analysis (LPA), atomic force microscopy, and transmission electron microscopy (TEM). It was found that the polymerization yield of the SD/PY (50/50) copolymers increased dramatically in the initial 2 h of polymerization and then slowly enlarged in the subsequent 22 h. However, the copolymerization yield for the polymerization time of 24 h exhibited a nonlinear dependence on the SD/PY molar ratio, i.e., a maximum at 10/90 and a minimum at 80/20. The number-average diameter, Dn, of the copolymer particles strongly depended on the SD/PY ratio, decreasing rapidly from 6402 to 291 nm as the SD/PY molar ratio changed from 30/70 to 50/50, whereas the polydispersity index, PDI = Dw/Dn (where Dw is the weight-average diameter), surprisingly maintained very small values, decreasing slightly from 1.21 to 1.08. The SD/PY (80/20) copolymer particles prepared with (NH4)2S2O8 as the oxidant had the smallest size of ca. 10 nm by TEM and the lowest Dw/Dn value of 1.03 by LPA, whereas the copolymer particles prepared with FeCl3 as the oxidant exhibited the second smallest size of ca. 20 nm by TEM and the highest conductivity. The conductivity of the SD/PY (50/50) copolymers rose first and then decreased with increasing polymerization time from 10 min to 24 h, exhibiting a maximum (0.217 S/cm) at 12 h. It is of interest that the copolymer particles with SD/PY molar ratios in the range between 50/50 and 80/20 surprisingly exhibited the smallest size, the narrowest size distribution, and the highest conductivity at the same time. In particular, the copolymer nanoparticles exhibited high purity, clean surfaces, good self-stability, high conductivity, and strong chemoresistance that were very important to nanomaterial processibility and application. The obtained copolymers were partially soluble in concentrated H2SO4, demonstrating a new direction for synthesizing a soluble pyrrole copolymer.

Probing Mercury Species−DNA Interactions by Capillary Electrophoresis with On-Line Electrothermal Atomic Absorption Spectrometric Detection

The interactions of inorganic mercury Hg(II), methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and phenylmercury (PhHg(I)) with DNA have been probed by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection (CE-ETAAS) in combination with circular dichroism and Fourier transform infrared spectroscopy. The CE-ETAAS assay allows sensitive probing of the level of DNA damage by mercury species, extraction of thermodynamic and kinetic information on the interactions of mercury species with DNA, and provides direct evidence for the formation of mercury species-DNA adducts. The binding affinity of mercury species to DNA increases in order of Hg(II) < EtHg(I) approximately PhHg(I) approximately MeHg(I). The interactions of mercury species with DNA follow a first-order kinetics for mercury species and zero-order kinetics for DNA. Mercury highly covalently coordinates to endocyclic and exocyclic N sites of DNA bases. However, the interactions of DNA with mercuric species cause no transition of the DNA original conformation. The results reveal that organomercuric species exhibit stronger affinity and faster binding to DNA and show more potential damage to DNA than Hg(II) in view of the kinetic and thermodynamic evaluations. Moreover, MeHg(I) exhibits the fastest binding to DNA, suggesting that MeHg(I) enjoys superiority over the other mercuric species for rapid formation of a stable complex with DNA, whereas Hg(II) shows the slowest binding to DNA. The present study provides new evidence and understanding of the binding modality of mercuric species to DNA.

Nanoscale surface patterns from 10(3) single molecule helices of biodegradable poly(L-lactic acid)

Atomic force microscopy, reflection absorption infrared spectroscopy, and X-ray reflectivity studies reveal that poly(L-lactic acid) molecules in Langmuir-Blodgett (LB) films exist as 10(3) helices over nearly the entire length of the polymer chain. This feature gives rise to LB films with highly ordered nanoscale smectic liquid crystalline-like surface patterns with low surface roughness and lamellar spacings that scale with molar mass. These studies provide a new approach for controlling surface morphology with a biodegradable polymer commonly used for drug delivery and tissue engineering.

Simple method for the stretching and alignment of single adsorbed synthetic polycations

Spin-coating of isolated positively charged macromolecules onto mica in the presence of octylamine was found to be a simple and general method of stretching and aligning the macromolecular chains. The contour length and molar mass for the stretched macromolecules can be directly measured by atomic force microscopy, which makes this method a very useful analytical tool. Moreover, the molecular height is increased by co-deposition with octylamine, which drastically improves the molecular resolution and allows even ultrathin polycations to be visualized. The reason for the key role of the octylamine is found in the formation of an ultrathin liquidlike alkylamine film, which reduces the surface energy of mica and weakens the interactions between the surface and the charged macromolecules.

Effect of Side-Chain Substituents on Self-Assembly of Perylene Diimide Molecules: Morphology Control

Effect of side-chain substitutions on the morphology of self-assembly of perylene diimide molecules has been studied with two derivatives modified with distinctly different side-chains, N,N'-di(dodecyl)-perylene-3,4,9,10-tetracarboxylic diimide (DD-PTCDI) and N,N'-di(nonyldecyl)-perylene-3,4,9,10-tetracarboxylic diimide (ND-PTCDI). Due to the different side-chain interference, the self-assembly of the two molecules results in totally different morphologies in aggregate: one-dimensional (1D) nanobelt vs zero-dimensional (0D) nanoparticle. The size, shape, and topography of the self-assemblies were extensively characterized by a variety of microscopies including SEM, TEM, AFM, and fluorescence microscopy. The distinct morphologies of self-assembly have been obtained from both the solution-based processing and surface-supported solvent-vapor annealing. The nanobelts of DD-PTCDI fabricated in solution can feasibly be transferred to both polar (e.g., glass) and nonpolar (e.g., carbon) surfaces, implying the high stability of the molecular assembly (due to the strong pi-pi stacking). The side-chain-dependent molecular interaction was comparatively investigated using various spectrometries including UV-vis absorption, fluorescence, X-ray diffraction, and differential scanning calorimetry. Compared to the emission of ND-PTCDI aggregate, the emission of DD-PTCDI aggregate was significantly red-shifted (ca. 30 nm) and the emission quantum yield decreased about three times, primarily due to the more favorable molecular stacking for DD-PTCID. Moreover, the aggregate of DD-PTCDI shows a pronounced absorption band at the longer wavelength, whereas the absorption of ND-PTCDI aggregate is not significant in the same wavelength region. These optical spectral observations are reminiscent of the previous theoretical investigation on the side-chain-modulated electronic properties of PTCDI assembly.

Electrochemical fabrication of conducting polymer nanowires in an integrated microfluidic system

In this paper, we introduce a new approach for the in situ electrochemical fabrication of an individually addressable array of conducting polymer nanowires (CPNWs) positioned within an integrated microfluidic device and also demonstrate that such an integrated device can be used as a chemical sensor immediately after its construction.