Yuan Ming Huang

Effect of Mortar-Pestle Grinding on Conductivity of Ferric Chloride Doped Polypyrrole

With four-probe technique, we investigated the effects of the mortar-pestle grinding on the conductivity of ferric chloride doped conducting polymer polypyrrole, which had been synthesized by in situ polymerizing the monomer pyrrole in aqueous solutions in the presence of the oxidant iron (III) chloride. As the mortar-pestle grinding duration increased from 0 to 4 hours, the conductivity of the synthesized polypyrrole was found to decrease from about 100 to 10 S/m. In the meantime, the sizes of the grinded polymeric particles were found to decrease from 40.6 to 3.36 uf06dm as the grinding duration increased from 0 to 4 hours. Our results demonstrated that the grinding shortened conjugation lengths of the polymeric chains should be responsible for the decrease in the conductivity of the polymer.

Mechanical Grinding: An Effective Method to Control the Conductivity of p-Toluene Sulfonic Acid Doped Polypyrrole

With four-probe and laser light scattering techniques, we have studied the dependencies of the conductivity and the particle sizes of p-toluene sulfonic acid doped polypyrrole on the mechanical grinding time. As the chemically synthesized polypyrrole was mechanically grounded in a mortar from 0 to 8 hours, its conductivity decreased from 607 to 10 S/m while and its particle size decreased from 27 to 4 uf06dm. If the mechanical grinding continued, the conductivity of the polymer was found to be up to 1680 S/m. Our results have demonstrated that mechanical grinding is an effective method to control the conductivity of the p-toluene sulfonic acid doped polypyrrole.

Organic Photovoltaic Cells Prepared with Toluene Sulfonic Acid Doped Polypyrrole

Organic photovoltaic cells were fabricated by sandwiching p-toluene sulfonic acid doped conducting polymer polypyrrole between indium-tin-oxide cathodes and aluminum anodes. The active polymeric layers could effectively absorb incident photons more than 75 % in the entire spectral region of 250~1100 nm. Upon light exposure, the short-circuit current and the open-circuit voltage were recorded up to 0.6 μA/cm2 and 60 mV, respectively, for the organic photovoltaic cells. The dynamics of the generation and decay of the photocurrent and photovoltage in our organic photovoltaic cells were investigated.

Transmission Spectra of One-Dimensional Photonic Crystal with a Centered Defect

In this letter, characteristic matrix method was used to calculate the transmittance spectra of the one-dimensional photonic crystals (1-DPCs) with single defects in the center. From altering the refractive indexes n2’ and n3’ respectively for the defect, the transmittance spectra were calculated. From them, it shown that for the certain numerical value n3’=5.0, during the course of n2’ increased from 1.1 to 3.5, when it upped to 2.0, there occurred defect band gap in the stop band gap, and the defect band gap is at frequencies between 0.24~0.30. Besides, for n2’ =2.0, when n3’ increased from 1.1 to 3.5, there also occurred defect band gap in the stop band gap, and the defect band gap is at frequencies between 0.26~0.32. In addition, in these two progresses, the transmittance increased firstly and then decreased in the defect band gap.

Size-Dependent Conductivity of Polypyrrole Doped with Anthraquinone-2-Sulfonic Acid Sodium

By varying the dopant-to-monomer ratio in a wide range of 0―110%, a series of polypyrroles doped with 9,10-anthraquinone-2-sulfonic acid sodium were synthesized by polymerizing the monomer pyrrole in aqueous solution of ferric chloride. The resulted polypyrroles were characterized with the four-probe, laser light scattering and differential thermal analysis, respectively. Our results indicated that the average particle size dominates the change in conductivity and thermal stability for the resulted polypyrrole at different dopant concentration.

Synthesis and Mesomorphic Properties of Three-Benzene-Ring Containing Bent-Core Liquid Crystal 1,3-Phenylene-bis[4-(nonylcarboyloxyl) benzylideneamine]

A bent-core compound with three benzene-ring cores 1,3-phenylene-bis [4-(nonylcarboyloxyl)benzyl ideneamine] was synthesized. Its mesomorphic properties were characterized with differential scanning calorimetry and polarized optical microscopy, respectively. This kind of bent-core compound exhibited mesophases in the temperature range of 155-185oC for the first cooling but cyclic heating and cooling could lower the phase transition temperatures for this bent-core liquid crystal. Our results demonstrated that bent-core molecules with three benzene-ring cores can also form mesophases as those five benzene-ring containing bent-core molecules do.

Terminal Length Dependent Transmission Spectra for One-Dimensional Photonic Crystals with a Centered Defect

The model of the one-dimensional photonic crystals (1-D PCs) with a centered defect with increasing number of layers was considered, and characteristic matrix method was used to calculate the transmittance spectra of the 1-D PCs. From the transmittance spectra, it shown that during the course of the number N of the layers of 1-D PCs’ one side symmetrical increased from 2 to 16, there occurred defect band gap in the stop band gap, when N upped to 16 , the defect band gap disappeared; besides, the defect band gap is at the frequencies around 0.30. In addition, in the progress of N increased from 3 to 16, the defect band gap reduced from the frequency range 0.0570 to 0.00, and the transmittance declined from 73.59% to 13.94% in the defect band gap.

Effect of Metallic Ions on Photoluminescence of Porous Silicon

In the present paper, we have not only investigated the top surface and cross-section morphology, but also measured photoluminescence spectra characteristic of porous silicon after deposition of metallic ions by electrochemical deposition employing scanning electron microscopy (SEM) and spectrometer, respectively. It is apparent from the SEM images that the microstructure of porous silicon is seriously ruined by the metallic ions deposited by electrochemical deposition. Most interesting is the finding that in the photoluminescence spectrum of porous silicon after the deposition of metallic ions such as AL3+ and Cu2+, the luminescence band gradually is quenched as the electrochemical deposition progressed. A careful consideration of the results obtained show that according to the basic theory of well-established quantum confinement model, the quenching of photoluminescence spectra of porous silicon may well be attributed to the microstructure fell into ruin. On the other side of the fence, we can interpret the physical origin of the phenomenon in view of the presence of metallic ions which give rise a series of energy level deep in the band gap of porous silicon.

Effect of Double Defects on Transmission Spectra of One-Dimensional Photonic Crystals

Considered the model of the one-dimensional photonic crystals (1-D PCs) with double defects, the refractive indexes (n2’, n3’ and n2’’, n3’’) of the double defects were 2.0, 4.0 and 4.0, 2.0 respectively. With parameter n2=1.5, n3=2.5, by theoretical calculations with characteristic matrix method, the results shown that for a certain number (14 was taken) of layers of the 1-D PCs, when the double defects abutted, there was a defect band gap in the stop band gap, while when the double defects separated, there occurred two defect band gaps in the stop band gap; besides, with the separation of the two defects, the transmittance of the double defect band gaps decreased gradually. In addition, in this progress, the frequency range of the stop band gap has a little increase from 0.092 to 0.095.

Efficient photoluminescence from thin films of polypyrrole

A soluble polypyrrole without any substituent groups was obtained by controlling the oxidation level of polypyrrole in the presence of oxygen. Upon the exposure to the 325 nm ultraviolet excitation from a helium-cadmium laser, thin films of the non-substituted polypyrrole could give off strong photoluminescence with its peak at about 530 nm. To elucidate the origin of the recorded strong photoluminescence, we measured the absorption spectra of the polypyrrole thin films with ultraviolet-visible absorption spectroscopy and our data indicated the appropriately oxidized polypyrrole are free of polarons. With the help of the electronic structures calculated with Hückel tight-binding method, the intense photoluminescence is interpreted in terms of the direct electronic transitions from the conduction band to valence band of the conjugated polymer.