Qinghua Li

Shape and Size Control of Oriented Polyaniline Microstructure by a Self-Assembly Method

Oriented polyaniline (PANI) microstructures (e.g., bulks, spheres, flakes, and fibers) were prepared without a template by polymerization at 80 degrees C and crystal growth at 0 degrees C and using a self-assembly method in the presence of hydrochloric acid (HCl) as the dopant. It was found that the shape and size of the resulting PANI microstructures depended on the HCl dosage and aniline concentration. Polyanilinium salt precipitates, as a templete, drive the formation of highly oriented PANI microstructures. The infrared and UV-vis absorption spectra and X-ray diffraction were used to characterize the molecular structures of the PANI microstructures. The results showed that their main structure was identical to those of the emeraldine salt form of PANI.

Enhancing the photoelectrical performance of dye-sensitized solar cells using TiO2:Eu3 + nanorods

TiO(2):Eu(3+) nanorods are hydrothermally grown and used to fabricate a bilayer film electrode in a dye-sensitized solar cell. A light-to-electrical energy conversion efficiency of 8.0% and a quantum efficiency of 93.7% (at 575 nm) is achieved in this solar cell. The high efficiency is due to the improvement of ultraviolet light harvesting via a down-conversion luminescence process by the Eu(3+) ion and the increase of light scattering by one-dimensional TiO(2).

A simple route to interpenetrating network hydrogel with high mechanical strength

A simple two-step method was introduced to improve the hydrogel mechanical strength by forming an interpenetrating network (IPN). For this purpose, we synthesized polyacrylate/polyacrylate (PAC/PAC), polyacrylate/polyacrylamide (PAC/PAM), polyacrylamide/polyacrylamide (PAM/PAM) and polyacrylamide/poly(vinyl alcohol) (PAM/PVA) IPN hydrogels. The PAC/PAC IPN and PAC/PAM IPN hydrogels showed compressive strength of 70 and 160kPa, respectively. For the PAM/PAM IPN and PAM/PVA IPN hydrogels, they exhibited excellent tensile strength of 1.2 and 2.8MPa, and elongations at break of 1750% and 3300%, respectively. A strain relaxation was also observed in the case of PAM series IPN hydrogels. From FTIR, TGA and SEM measurements, we confirmed that physical entanglement, hydrogen bonds and chemical crosslinking played major roles in improving hydrogel strength and toughening. The two-step technique contributes to the understanding of ideal networks, provides a universal strategy for designing high mechanical strength hydrogels, and opening up the biomedical application of hydrogels.

Synthesis of polyacrylate/polyethylene glycol interpenetrating network hydrogel and its sorption of heavy-metal ions

Abstract A simple two-step aqueous polymerization method was introduced to synthesize a polyacrylate/polyethylene glycol (PAC/PEG) interpenetrating network (IPN) hydrogel. On the basis of the effects of the ratio of PAC to PEG, neutralization degree, heavy-metal ion concentration, and temperature on the adsorption behavior of PAC/PEG IPN hydrogel toward Ni2 +, Cr3 + and Cd2 +, the preparation conditions were optimized. In our system, the greatest amount of Ni2 +, Cr3 + and Cd2 + adsorbed were 102.34, 49.38 and 33.41 mg g- 1, respectively. The adsorption abilities of a dried PAC/PEG composite and a swollen PAC/PEG IPN hydrogel were compared. It was found that the efficiency of removing metal ions using the swollen hydrogel was greater than that using the dried composite. The adsorption mechanism and model are also discussed.

Preparation and electrical conductivity of SiO2/polypyrrole nanocomposite

In the present study we have chemically polymerized silica/polypyrrole (SiO2/PPy) nanocomposite in the presence of sodium dodecyl benzene sulfate (SDBS) as dopant and iron chloride (FeCl3) as oxidant. The SiO2/PPy nanocomposite presents an electrical conductivity of 32.41xa0Sxa0cm−1 and percolation threshold of 20 wt%. The resulting SiO2/PPy nanocomposites have been extensively characterized in terms of their molecular structure, particle size, morphology, stability, and electroactivity. These SiO2/PPy particles have a rather polydisperse morphology. The effects of synthesis parameters such as oxidant, PPy, SDBS, reaction temperature and time, on the electrical conductivity of the nanocomposite have been detailedly optimized. And the conducting nanocomposite presented a good environmental stability.

High efficiency dye-sensitized solar cell based on novel TiO2 nanorod/nanoparticle bilayer electrode.

High light-to-energy conversion efficiency was achieved by applying novel TiO2 nanorod/nanoparticle (NR/NP) bilayer electrode in the N719 dye-sensitized solar cells. The short-circuit current density (J SC), the open-circuit voltage (V OC), the fill factor (FF), and the overall efficiency (η) were 14.45 mA/cm(2), 0.756 V, 0.65, and 7.1%, respectively. The single-crystalline TiO2 NRs with length 200-500 nm and diameter 30-50 nm were prepared by simple hydrothermal methods. The dye-sensitized solar cells with pure TiO2 NR and pure TiO2 NP electrodes showed only a lower light-to-electricity conversion efficiency of 4.4% and 5.8%, respectively, compared with single-crystalline TiO2 NRs. This can be attributed to the new NR/NP bilayer design that can possess the advantages of both building blocks, ie, the high surface area of NP aggregates and rapid electron transport rate and the light scattering effect of single-crystalline NRs.

Synthesis of polyacrylate/polyethylene glycol interpenetrating network hydrogel and its sorption for Fe3+ ion

A simple two-step aqueous polymerization method was introduced to synthesize polyacrylate/polyethylene glycol (PAC/PEG) interpenetrating network (IPN) hydrogel. The sorption behaviors and mechanism were studied by the sorption of PAC/PEG IPN hydrogel to Fe3+ ion from aqueous solution. The experimental results revealed that the adsoption amount of Fe3+ ion using swollen hydrogels was much higher than that using the dried composite, they were 75.69 mg/g and 14.25 mg/g, respectively. The parameters, such as neutralization degree, acrylic acid (AA) dosages and temperature, on the sorption amount of PAC/PEG IPN hydrogel were detailedly investigated.

Layer-by-layer self-assembly of conducting multilayer film from poly(sodium styrenesulfonate) and polyaniline.

Highly oriented polyaniline (PANI) fiber was prepared by a polymerization at higher temperature and growth in lower temperature. Poly(sodium styrenesulfonate)/polyaniline multilayer film (PSS/PANI)(n) was layer-by-layer molecular-level self-assembled by a simple technique. The morphology and structure of the oriented PANI fiber were characterized, showing an emeraldine state and ordered molecular structure. The growth process and surface topography of the (PSS/PANI)(n) multilayer film were characterized by UV-vis spectroscopy and atomic force microscopy. Absorbance plotted against the bilayers exhibited a linear dependence, indicating a progressive and uniform deposition process of the multilayer film. The (PSS/PANI)(n) multilayer film exhibited an electrical conductivity in the order of 1 S cm(-1), and when bilayer number exceeded a threshold value of 4, the conductivity of the multilayer film increased dramatically. The electrochemical properties were studied through cyclic voltammograms, and it was found that the electrochemical activity of the (PSS/PANI)(n) film increased with the increase of the bilayer number.

A simple route to high-strength hydrogel with an interpenetrating polymer network

Abstract Hydrogels have potential applications in many fields, but the poor mechanical strength has limited their further development. In this article, we designed a simple route to high-strength interpenetrating polymer network (IPN) hydrogel from polyacrylamide (PAAm) and poly(vinyl alcohol) (PVOH). The highest tensile strength and elongation were 2.4 Mpa and 4300 %, respectively. It was found that the hydrogel strength depended on the chemical crosslinking, physical entanglement and PVOH precipitates. Because of the hydrogen bonding interactions and self-crosslinking, the structure of PVOH transferred from crystal to amorphous. PVOH precipitates scattered in the crosslinked PAAm matrix which dispersed the stress and improved the hydrogel toughness. The simple method is versatile in synthesizing high-strength IPN hydrogels using many kinds of polymer species.

Growth of large-scaled polypyrrole fibers using polyacrylamide as modifier

Abstract We first report a novel route to synthesize centimeter-scaled polypyrrole (PPy) fiber in the presence of oligo-polyacrylamide. The Fourier transform infrared and ultraviolet-visible spectra reveal that the fiber is in high conductive state. The PPy fibers have a uniform diameter of 300 μm, and length varying from several millimeters to 4 cm. The temperature dependence of electrical conductivity reveal that the transport properties of PPy fibers should be dominantly characterized by phonon-assisted hopping mechanism. Polymer-directed crystal growth may provide promising routes to rational synthesis of various ordered organic materials with complex form and structural specialization.