Counterions in poly(allylamine hydrochloride) and poly(styrene sulfonate) layer-by-layer films

The amount of counterions in layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) has been determined with X-ray photoelectron spectroscopy (XPS) for films prepared from solutions with various NaCl concentrations. Sodium and chloride counterions are present in LBL films produced from salt solutions, which are located at the surface and in the bulk of the films. The percentage of bulk counterions increases with the ionic strength of the polyelectrolyte before reaching a constant value. The bulk sodium/sulfur percentage ratios tend to 0.8 for samples washed with pure water and for samples washed with NaCl aqueous solutions, while the bulk chlorine/nitrogen percentage ratios tend to 0.5 for the same samples. The ratio between the percentages of polyelectrolyte ionic groups lies close to unity for all samples, indicating that counterions do not contribute to charge compensation in the polyelectrolyte during the adsorption process. The presence of counterions in LBL films is explained by Manning condensation near the polyelectrolyte ionic groups, leading to inter-polyelectrolyte ionic bondings via ionic networks. It is believed that condensation leads to the formation of NaCl crystallites in these LBL films, which was confirmed by X-ray diffraction measurements.     

Comparative studies of solid‐state synthesized poly(o‐methoxyaniline) and poly (o‐toluidine)

Poly(o‐methoxyaniline) (POMA) and poly(o‐toluidine) (POT) salts doped with different acids (methanesulphonic acid (MeSA), trifluoroacetic acid (TFA), and hydrochloric acid (HCl)) were synthesized by using solid‐state polymerization method. The polymers were characterized by Fourier transform infrared (FTIR) spectra, ultraviolet–visible (UV–Vis) spectrometry, X‐ray diffraction (XRD), cyclic voltammetry (CV), and conductivity measurements. Transmission electron microscopy (TEM) was done to study the morphologies of POMA and POT salts. The FTIR and UV‐Vis absorption spectra revealed that the reduced phase was predominant in POMA salts, and the pernigraniline phase was predominant in POT salts. It was found that POMA salts displayed higher doping level and conductivity. In contrast, POT salts were lower at doping levels and conductivity. In accordance with these results, the electrochemical activity was also found to be lower in POT salts. The XRD patterns showed that the POMA salts displayed higher crystallinity than POT salts. The results from TEM revealed that the morphologies of POMA salts were different from those of POT salts. Copyright © 2008 John Wiley & Sons, Ltd.     

Electroactive LbL films of metallic phthalocyanines and poly(<Emphasis Type="Italic">0</Emphasis>-methoxyaniline) for sensing

Multilayered nanostructured films have been widely investigated for electrochemical applications as modified electrodes, including the layer-by-layer (LbL) films where properties such as thickness and film architecture can be controlled at the molecular level. In this study, we investigate the electrochemical features of LbL films of poly(o-methoxyaniline; POMA) and tetrasulfonated phthalocyanines containing nickel (NiTsPc) or copper (CuTsPc). The films displayed well-defined electroactivity, with redox pairs at 156 and 347 mV vs SCE, characteristic of POMA, which allowed their use as modified electrodes for detecting dopamine and ascorbic acid at concentrations as low as 10⁻⁵ M. This paper is dedicated to Prof. Francisco Nart, in memoriam.     

Self-assembly of multilayer films containing gold nanoparticles via hydrogen bonding

Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV-vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.     

Template synthesis of polyaniline and poly(2-methoxyaniline) nanotubes: comparison of the formation mechanisms

The process of polyaniline (PANI), poly(2-methoxyaniline) (POMA) nanotubes formation was investigated. Polyaniline and poly(2-methoxyaniline) nanotubes were prepared by chemical in situ deposition within the pores of polycarbonate membranes. It was found that the formation of polyaniline and poly(2-methoxyaniline) proceeds by two substantially different mechanisms. In the case of PANI, the polymer is first formed in the polymerization solution (the solution containing the monomer and oxidant, where the polycarbonate substrate is placed), and then it precipitates on/into the membrane. In the case of POMA, the oxidized 2-methoxyaniline molecules are first adsorbed on polycarbonate surface, and then, as a consequence of their accumulation, they recombine to form the polymer.     

Highly ion conductive poly(ethylene oxide)-based solid polymer electrolytes from hydrogen bonding layer-by-layer assembly

We report the development of a solid polymer electrolyte film from hydrogen bonding layer-by-layer (LBL) assembly that outperforms previously reported LBL assembled films and approaches battery integration capability. Films were fabricated by alternating deposition of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) layers from aqueous solutions. Film quality benefits from increasing PEO molecular weight even into the 10(6) range due to the intrinsically low PEO/PAA cross-link density. Assembly is disrupted at pH near the PAA ionization onset, and a potential mechanism for modulating PEO:PAA ratio within assembled films by manipulating pH is discussed. Ionic conductivity of 5 x 10(-5) S/cm is achievable after short exposure to 100% relative humidity (RH) for plasticization. Adding free ions by exposing PEO/ PAA films to lithium salt solutions enhanced conductivity to greater than 10(-5) S/cm at only 52% RH and tentatively greater than 10(-4) S/cm at 100% RH. The excellent stability of PEO/PAA films even when exposed to 1.0 M salt solutions led to an exploration of LBL assembly with added electrolyte present in the adsorption step. Fortuitously, the modulation of PEO/PAA assembly by ionic strength is analogous to that of electrostatic LBL assembly and can be attributed to electrolyte interactions with PEO and PAA. Dry ionic conductivity was enhanced in films assembled in the presence of salt as compared to films that were merely exposed to salt after assembly, implying different morphologies. These results reveal clear directions for the evolution of these promising solid polymer electrolytes into elements appropriate for electrochemical power storage and generation applications.     

Effect of chloroform on the structure and gas-separation properties of poly(ether imides)

The FTIR spectra of poly(ether imide) films prepared from their chloroform solutions were recorded in a wide temperature interval. The cast films were shown to contain residual solvent. This residual solvent existed in films as unbound chloroform that may be removed by heating to 60–70°C and as bound chloroform that is involved in complex formation with polymers and may be removed by heating at temperatures close to their glass transition temperatures (180°C). Quantum-chemical calculations were performed for structures that model fragments and monomer units of poly(ether imides), as well as their complexes with chloroform. Chloroform was shown to be capable of preferential binding with an oxygen atom in a Ph-O-Ph′ fragment via hydrogen bonds. In this case, the conformational set of poly(ether imide) chains is changed. The above evidence is invoked to explain changes in transport characteristics with time for poly(ether imide) films cast from chloroform solutions.     

Miscibility windows for poly(styrene-co-vinyl phenol) blends with poly(alkyl methacrylate)s: Further comparisons of theoretical predictions to FTIR experimental data

We report the results of theoretical and experimental studies of styrene-co-vinyl phenol (STVPh) copolymer blends with poly(n-octyl methacrylate) (POMA) and poly(n-decyl methacrylate) (PDMA). This work is a natural extension to our recently reported studies of the phase behavior of analogous STVPh blends with poly(n-butyl methacrylate) (PBMA) and poly(n-hexyl methacrylate) (PHMA) where we employed an association model together with parameters obtained from studies of miscible homopolymer blends. The theoretically calculated miscibility maps for STVPh copolymer blends with the homologous series of poly(n-alkyl methacrylates) (PAMA) are in fine agreement with experiment.     

Electrochemical polymerization of poly(thiophene-3-acetic acid), poly(thiophene-co-thiophene-3-acetic acid) and determination of their molar mass

The electrochemical preparation and molar mass characterization of conducting polymers, poly(thiophene-3-acetic acid) (poly(TPAA)), and poly(thiophene-co-thiophene-3-acetic acid) (poly(TP/TPAA)) are reported. RRDE results revealed that, unlike other conducting polymers, current efficiency during the deposition of poly(TPAA) is by far less than 1 due to significant solubility of the polymer. Up to 48% of the oxidation products of the disc electrode can dissipate into the bulk solution. These dissipated species are polymers in oxidized form and reactive towards reductant originally present in the coating solution. The low current efficiency necessitates the use of relatively high monomer concentration and high polymerization potential to obtain a conducting poly(TPAA) film. Characterization with gel permeation chromatography (GPC) of molar mass and its distribution has been carried out. The results show that up to 65% to 85% of the whole polymers are comprised of big molecules containing over 2000 monomer units, which indicates the possibility of cross-linking of polymer chains. The remaining parts of the polymers are relatively short chains containing several to dozens of monomers. Increase of TPAA content in the copolymers leads to better solubility and higher molar mass. The latter is accompanied by greater electronic conjugation in the polymer chains.     

ELECTROSYNTHESES OF FREE-STANDING POLY(THIOPHENE-3-ACETIC ACID) FILM IN MIXED ELECTROLYTES OF BORON TRIFLUORIDE DIETHYL ETHERATE AND TRIFLUOROACETIC ACID

High quality free-standing poly(thiophene-3-acetic acid)(PTAA),a water-soluble polythiophene derivative,was successfully electrosynthesized in boron trifluoride diethyl etherate(BFEE)+ 25%(by volume)trifluoroacetic acid(TFA)at lower potential(0.38 V versus Pt).The carboxyl group makes PTAA highly soluble in water,facilitating its potential application as a blue-light-emitting material.PTAA films with conductivity of 7 S cm"1 obtained from this medium showed better redox activity and thermal stability.The structure and morphology of the polymer were studied by UV-Vis,FT-IR, ~1H-NMR spectra and scanning electron microscopy,respectively.     

Polyelectrolyte multilayers prepared from water-soluble poly(alkoxythiophene) derivatives.

Electronically conducting polyanion and polycation based on poly(alkoxythiophene) derivatives, poly-3-(3'-thienyloxy)propanesulfonate (P3TOPS) and poly-3-(3'-thienyloxy)propyltriethylammonium (P3TOPA) have been synthesized. Both polymers are water-soluble and exhibit high conjugation length in solution and in the solid state. These polyelectrolytes were used to prepare conducting and electroactive polyelectrolyte multilayers by the sequential layer-by-layer adsorption technique. In aqueous solutions multilayers of P3TOPS with inactive polyelectrolytes (e.g., poly(diallyldimethylammonium chloride), PDADMA) displayed electrochemical and optical behavior similar to polythiophene films prepared in organic media. Their in-plane conductivity was low (ca. 1.6 x 10(-)(5) S cm(-)(1)). The conductivity could, however, be increased by a factor of ca. 40 in "all-thiophene" films, in which P3TOPA was substituted for the inactive polycation (PDADMA). The interpenetration of layers is of prime importance in films containing conducting components. The interpenetration of P3TOPS was studied by measuring the charge-transfer rate across an insulating polyelectrolyte multilayer between the substrate and the P3TOPS layer with modulated electroreflectance. The extent of interpenetration was 8-9 polyelectrolyte layers, the length scale (7-15 nm) depending on the nature of the insulating layer and, especially, on the ionic strength of the solution used for the adsorption of P3TOPS.     

Fluorescence staining and confocal laser scanning microscopy study of hydrogen-bonded poly(vinylpyrrolidone)/poly(acrylic acid) film

Poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) were layer-by-layer (LBL) assembled to prepare the thin films based on hydrogen-bonding complexation. The hydrogen-bonded PVPON/PAA films were incubated in acidic, neutral and basic vapors separately. To study the morphologies after incubation, the films were stained by pH-sensitive fluorescent dyes using chemical and physical ways, and investigated with confocal laser scanning microscope (CLSM). The chemical way (labeling) was covalently linking fluoresceinamine (FAM) to some monomer units of PAA while the physical way was adsorbing rhodamine B (RB) molecules from dilute solution. Atomic force microscope (AFM) was combined with CLSM to find that after incubation in neutral or basic vapor the hydrogen-bonded PVPON/PAA films form porous structure and the pores are through the whole film.     

自掺杂基团对聚苯胺自组装膜电化学性能的影响

基于离子相互作用,实现了以聚苯胺(PANI)为聚阳离子,以聚(邻氨基苯甲酸)(PCAN)、聚(邻氨基苯磺酸)(PSAN)为聚阴离子的层-层自组装,形成层厚均匀的全共轭超薄功能膜.由于磺酸基—SO3-的电负性高于—COO-,使得PANI-PSAN自组装膜沉积量小于PANI-PCAN;电化学实验结果显示,由于PCAN和PSAN的导电性均弱于PANI,所以两种自组装膜的电化学性能取决于PANI,但同时受到羧酸、磺酸基团的较大影响,使得PANI-PCAN自组装膜的电化学性能要优于PANI-PSAN.     

Composite thin film by hydrogen-bonding assembly of polymer brush and poly(vinylpyrrolidone)

Based on hydrogen-bonding layer-by-layer (LBL) assembly in aqueous solution, poly(vinylpyrrolidone) (PVPON) and a spherical polymer brush with a poly(methylsilsesquioxane) (PSQ) core and poly(acrylic acid) (PAA) hair chains were used to fabricate composite multilayer thin films. Hydrogen bonding as the driving force was confirmed by FT-IR spectrometry. A simple method (Filmetric F20) was introduced to determine the thickness and refractive index of the films. The film thickness was found to be a linear function of the number of bilayers. The average increase in thickness per bilayer is 28.3 nm. The film morphology was characterized with scanning electron microscopy and atomic force microscopy. The images obtained from the two instruments show a great resemblance. The films were further calcined to get an inorganic film by removing the organic components, or treated with tetrabutylammonium fluoride (TBAF) to remove the PSQ core and get an organic film. The optical properties and morphological changes induced by these treatments were also studied.     

PH effects in the complex formation and blending of poly(acrylic acid) with poly(ethylene oxide)

The effect of pH on the complex formation between poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) has been studied in aqueous solutions by turbidimetric and fluorescent methods. It was shown that the formation of insoluble interpolymer complexes is observed below a certain critical pH of complexation (pH(crit1)). The formation of hydrophilic interpolymer associates is possible above pH(crit1) and below a certain pH(crit2). The effects of polymer concentrations in solution and PEO molecular weight as well as inorganic salt addition on these critical pH values were studied. The polymeric films based on blends of PAA and PEO were prepared by casting from aqueous solutions with different pHs. These films were characterized by light transmittance measurements and differential scanning calorimetry. The existence of the pH value above which the polymers form an immiscible blend was demonstrated. The transitions between the interpolymer complex, miscible blend, and immiscible blend caused by pH changes are discussed. The recommendations for preparation of homogeneous miscible films based on compositions of poly(carboxylic acids) and various nonionic water-soluble polymers are presented.     

Multilayered assemblies composed of brilliant yellow and poly(allylamine) for an optical pH sensor.

Multilayered thin films containing poly(allylamine) (PAA) and brilliant yellow (BY) were prepared on a quartz slide by a layer-by-layer (LBL) deposition technique. The UV-visible spectra of the PAA/BY films were sufficiently changed depending upon the pH value of the solution in which the film was immersed. The response of the PAA/BY films was very fast (within a second) upon pH change from 9.0 to 5.0, while the response time was ca. 100 s upon pH change from 5.0 to 9.0.     

Thermally stable sulfone-containing poly(amide-imides)

Novel sulfone containing poly(amide-imides) have been prepared by reacting 3,4-dicarboxy-4′-(chloroformyl)-diphenylsulfone dianhydride with various aromatic diamines. Relatively high molecular weight polymers were obtained by using a two-step procedure. Transparent poly(amide-imide) films, varying in color from dark yellow to colorless, were formed by thermally treating polyamic acid solutions. All films showed good thermal stability.     

Simple method for the preparation of DNA-poly(o-methoxyaniline) hybrid: structure, morphology, and uncoiling of poly(o-methoxyaniline) on the DNA surface

The DNA-poly(o-methoxyaniline) (POMA) hybrid is prepared by mixing aqueous solutions of POMA [emeraldine salt (ES), doping level [Cl]/[N] = 0.52] and sodium salt of DNA (Na-DNA) and is then freeze-dried after 4 days. Three different compositions (WDNA = 0.25, 0.5, and 0.75, WDNA is the weight fraction of DNA) of the hybrids are prepared. The SEM pictures show a gradation in morphology; for example, for WDNA = 0.75, fibrils are present but, at lower DNA concentration, a fibrillar network structure of the hybrid is observed. The circular dichroism (CD) spectra of the hybrid solutions indicate unchanged DNA conformation and WAXS patterns indicate intact crystal structure of DNA in the hybrid. The UV-vis spectra suggest no denaturation of DNA during the blending process. The UV-vis spectra of the hybrids in aqueous medium show a gradual red shift of the pi band to polaron band transition with time. The plots of these wavelengths with time are sigmoidal, indicating the autocatalytic nature of the process. With an increase in the temperature, the rate of the red shift of the above peak is faster. Arrhenius analysis of the rate (1/tau700 where tau700 is the time required to reach the absorption maximum at the wavelength 700 nm) yields straight lines for the three hybrid compositions with activation energy values of 13-15 kcal/mol. These values are almost equal to the activation energy values of conformational transition of other polymers, supporting the red shift in UV-vis spectra occurs from conformational transition. DNA offers a surface where POMA gets adsorbed and the stable conformational transition resulting in the uncoiling of the POMA chain occurs through repulsive interaction among bound radical cations of POMA (ES) on the DNA surface. The conductivity of the hybrids is on the order of 10(-6) S/cm, and the I-V characteristic curves indicate the semiconducting nature of the hybrids.     

Synthesis and electrical conductivity of poly(arylene vinylene). I. Poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene)

The highly conjugated aromatic polymers, poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene), were obtained from their water soluble, sulfonium salt precursor polymers. Films of these polymers were reacted with either AsF₅ or I₂ vapor. Poly(2,5-dimethoxyphenylene vinylene) showed increases in electrical conductivity of up to 14 to 15 orders of magnitude for these two dopants, while an 8 to 9 order of magnitude increase was observed for poly(2,5-dimethylphenylene vinylene) with the same dopants. The synthesis of the precursor polymers, the properties and elimination reactions of films of the precursors, the doping reactions, and the conductivities of the resulting phenylene vinylene films are discussed.     

Self-assembled films of poly(o-ethoxyaniline) complexed with sulfonated lignin

The interaction of poly(o-ethoxyaniline) (POEA) doped with HCl and sulfonated lignin (SL) was investigated using UV–Vis spectroscopy in order to probe the influence of pH and quantity of SL on the formation of a polyelectrolyte complex. The introduction of SL into the HCl doped POEA solution screens the positive charges of the protonated POEA allowing further protons to be pumped into the conducting polymers thus increasing its doping level. In addition, the strong interaction between these two electrolytes caused POEA to remain doped within a wide pH range. Layers were built from aqueous solutions of the complex formed by POEA and SL which were alternated with either pure POEA or sulfonated polystyrene in the form of layer-by-layer films. The resulting multilayer films remained doped even at pH 9.0, due to the strong complex formation, which prevents POEA from deprotonating. Surface potential measurements showed that the potential for the POEA+SL complex is more positive than for films with each layer investigated separately, thus confirming the strong interaction between POEA and SL.