Danming Chao

Single-chain polymer nanoparticles via reversible disulfide bridges

We report the fabrication of single-chain polymer nanoparticles (SCNP) that can reversibly undergo a coil to particle transition via formation and cleavage of intramolecular disulfide cross-links. Characterization of this behaviour via shifts in SEC retention time confirm the changes in solution conformation in response to oxidative or reductive stimuli.

Intra-chain photodimerization of pendant anthracene units as an efficient route to single-chain nanoparticle fabrication.

An efficient route to architecturally defined, sub-20 nm soft nanoparticles fabricated from single polymer chains via intramolecular photodimerization of pendant anthracene units is presented. Photodimerization is confirmed by the disappearance of the characteristic anthracene π-π* absorption peak at ≈ 360 nm measured by UV-vis spectroscopy. Size exclusion chromatography (SEC) with UV, multi-angle light scattering (MALS), and viscometric detection confirms that as photodimers form, the chains fold to form nanoparticles, demonstrated by shifts in the SEC traces to longer retention times as a function of increased irradiation time. These shifts indicate a reduction in hydrodynamic radius, corroborated and quantified by viscometric data. MALS detector traces reveal the presence of a small amount of chain-chain coupling during this process, but confirm that this is primarily a single-chain phenomenon. Electron microscopy provides visual confirmation of nanoparticle formation.

Poly(acrylic acid)-guided synthesis of helical polyaniline/CdS composite microwires

Polyaniline (PANI) composite microwires containing CdS nanoparticles were synthesized guided by poly(acrylic acid) (PAA). It was found that the morphology of the composite microwires was affected by the concentration of PAA. When the concentration of PAA was lower than 0.1 mg ml−1, the PANI/CdS composite was wires. However, no wire-like structures of PANI/CdS composites were formed when the concentration of PAA was higher than 1.0 mg ml−1. The complex of CdS nanoparticles with PANI matrix was affected by the molar ratio of CdS to aniline. When the molar ratio was 1:75, CdS nanoparticles were well combined with PANI matrix. However, when the molar ratio was 1:150, no CdS nanoparticles were combined with PANI wires. SEM, TEM, FTIR and XRD characterized the PANI/CdS composite microwires and proved that the CdS nanoparticles are combined with the PANI matrix in some conditions, and TEM proved that some of the microwires are in fact of helical shape. The photoluminescence of CdS is slightly affected by its combination with the PANI matrix.

Preparation of unique PEDOT nanorods with a couple of cuspate tips by reverse interfacial polymerization and their electrocatalytic application to detect nitrite

By using Ce(SO4)2·4H2O as an oxidant and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as a surfactant, unique poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods with a couple of cuspate tips were successfully prepared by reverse interfacial polymerization. The morphology of these PEDOT nanorods was very regular and well-dispersed with widths and lengths from one tip to another tip mostly in the range 40–60 nm and 370–460 nm, respectively. The chemical structure and formation mechanism of PEDOT nanorods are discussed in detail by several analysis methods. AOT played an important role during the formation of PEDOT nanorods. It could be combined with Ce4+ to form a unique template for the polymerization of 3,4-ethylenedioxythiophene (EDOT) in the cylindrical micelles formed by n-hexane, H2O and AOT. Furthermore, the application of PEDOT nanorod-modified glassy carbon electrode (GCE) as an electrochemical sensor for detecting nitrite was also investigated. Due to their good dispersibility and large surface area, PEDOT nanorods exhibited good linearity and sensitivity of cyclic voltammetry (CV) responses as well as amperometric responses for electrocatalytic oxidation of nitrite. It resulted in PEDOT nanorods acting as a good steady and sensitive electrode material for detecting nitrite.

A facile strategy to decorate Cu9S5 nanocrystals on polyaniline nanowires and their synergetic catalytic properties

Here, we demonstrated a novel method to decorate Cu9S5 nanocrystals on polyaniline (PANI) nanowires using the dopant of mercaptoacetic acid (MAA) in the PANI matrix as the sulfur source under a hydrothermal reaction. TEM images showed that Cu9S5 nanocrystals with a size in the range of 5–20 nm were uniformly formed on the surface of PANI nanowires. Significantly, the as-prepared PANI/Cu9S5 composite nanowires have been proven to be novel peroxidase mimics toward the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Due to the synergetic effects between polyaniline nanowires and Cu9S5 nanocrystals, the obtained PANI/Cu9S5 composite nanowires exhibit superior catalytic activity over the independent components. This work not only presents a simple and versatile method to decorate semiconductor nanocrystals on the surface of conducting polymer nanostructures, but also provides fundamental guidelines for further investigations into the synergetic effect between conducting polymers and other materials.

Highly stable electrochromic and electrofluorescent dual-switching polyamide containing bis(diphenylamino)-fluorene moieties

Two kinds of electroactive polyamides with bis(diphenylamino)-fluorene units acting as electroactive fluorophores were prepared via condensation polymerization from a novel diamine, N,N′-bis(4-aminophenyl)-N,N′-bis(4-methoxyphenyl)-2,7-diamino-9,9-dimethylfluorene, with cycloaliphatic and aromatic dicarboxylic acids, respectively. These polyamides exhibited excellent solubility in various organic solvents and outstanding thermal stability. Cyclic voltammograms of the polyamide films revealed two reversible redox couples with half-wave potentials at 0.54–0.56 and 0.75–0.78 V, respectively. The polyamide films showed excellent reversible stability of multicolor electrochromic characteristics (colorless-orange-blue) after over 1000 cyclic switches. Compared with the polyamide derived from aromatic dicarboxylic acids, the polyamide derived from cycloaliphatic dicarboxylic acid exhibited strong fluorescence with quantum yield up to 50.2%. Furthermore, the fluorescence could be reversibly modulated by electrochemical redox with superior stability and a high contrast ratio of 152.

Fabrication of electrochemically responsive surface relief diffraction gratings based on a multifunctional polyamide containing oligoaniline and azo groups

A novel, well-defined multifunctional polyamide bearing pendent aniline tetramer groups has been synthesized via low temperature solution polycondensation. The simultaneous presence of these two functional groups allows the polyamide to display the properties of azo-chromophore and oligoaniline, such as photoinduced birefringence and reversible electroactivity. The electrochromic performance of the polyamide shows the optical change in absorptivity depends on the various redox states of oligoaniline upon electrochemical switching. It is well known that a change in absorptivity is accompanied by a concomitant change in refractive index. By taking advantage of this effect and using the single step fabrication of surface relief gratings based on azo-chromophore, we have fabricated optical diffraction gratings with which the diffraction efficiency can be modulated by an electrochemical signal. Although patterned electroactive films have been made by many techniques, the copolymer approach employing the simple one-step surface relief gratings process displays optimal properties with respect to modulation depth and convenience, which avoids complicated electropolymerization steps or photochemical reactions. The electrochemically-induced modulation in the diffraction efficiency of the polyamide is believed to arise primarily from the effect of the redox state on the films refractive index.

Fabrication of electroactive oligoaniline functionalized poly(amic acid) nanofibers for application as an ammonia sensor

A novel, well-defined, multifunctional electroactive poly(amic acid) (EPAA) containing oligoaniline pendants was synthesized by a one-step synthetic route. The structure was confirmed spectroscopically via nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectra, and the thermal stability was probed via thermogravimetric analysis (TGA). The oligoaniline pendants imparted excellent electroactivity, photoresponsiveness to chemical redox and electrochemical modulation, and expectable electrochromic performance to the obtained EPAA. Leucoemeraldine base EPAA (LEPAA), emeraldine base EPAA (EEPAA) and HCl-doped emeraldine base EPAA (HCl-doped EEPAA) nanofibers were fabricated by electrospinning and were characterized by scanning electron microscopy (SEM) to test their morphology, and a contact angle goniometer was used to test their hydrophilicity. The as-prepared HCl-doped EEPAA nanofibers were then evaluated for their ability to sense ammonia.

Electroactive polymer with oligoanilines in the main chain and azo chromophores in the side chain: synthesis, characterization and dielectric properties

By an oxidative coupling polymerization approach, we have synthesized a novel electroactive polymer with good solubility containing alternating phenyl-capped aniline tetramer in the main chain and azo chromophores in the side chain. Dielectric properties of the as-synthesized polymer were investigated in detail and gratifying results have been observed. Firstly, a large enhancement in the dielectric constant was achieved utilizing the method of doping the conjugated oligoaniline segments with hydrochloric acid. Secondly, the adjustment of dielectric constant was implemented primarily by means of exposing the samples to UV and visible irradiation, mainly owing to the photoisomerization derived from azo chromophores in the side chain. The detailed characteristics of the as-synthesized polymer were systematically studied by Fourier-transform infrared (FTIR) spectra, nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). UV-vis spectra were used to monitor the photoisomerization and doping process of the polymer. The thermal characteristics of the polyamide were evaluated by thermogravimetric analysis (TGA). Moreover, the electrochemical activity of the polymer was explored by cyclic voltammogram (CV) measurement, showing that the intrinsic electroactivity of the oligoaniline was maintained in the polymer.

Tuning the fluorescent response of a novel electroactive polymer with multiple stimuli.

A novel polymer featuring oligoaniline pendants that exhibits reversible electroactivity and good electrochromic properties with high contrast value, acceptable switching times, and excellent coloration efficiency is presented. This polymer can undergo reversible changes in fluorescence in response to reductive and oxidative chemical stimulus, pH, and electrical potential. The fluorescence switching operation shows reasonable reversibility and reproducibility when subjected to multiple stimuli. In this elegant fluorescence switching system, the oligoaniline pendants are used as fluorophore and regulatory units simultaneously.