Mujie Yang

Investigations on the ion transport mechanism in conducting polymer films

The change in the electrical properties were investigated as a function of relative humidity by several techniques (among them the electrochemical impedance) for different ion-conducting polymers, sprayed as films on interdigitated gold electrodes. It was found that the equations valid for electrolytic solutions fit the experimental data. In particular, the Onsager equation, applied to the relevant parameters of the polymeric films, describes the change in the film resistance as a function of relative humidity satisfactorily.

Charge transport mechanism in pressed pellets of polymer proton conductors

The charge transport inside some polymer proton conductors, prepared by chemical doping of poly(propargyl alcohol) and poly(p-diethynylbenzene) with acids, or by electrochemical polymerisation of thionaphtheneindole, has been investigated. All the systems, studied as powder pressed pellets between two gold electrodes, show very low electrical conductivity due to electrons motion. In presence of environmental humidity the conductivity increases dramatically as a consequence of proton migration through the material. A mechanism for the charge transport through the materials, based on the proton conductivity of a thin layer of acid aqueous solution adherent to the polymer grains, has been hypothesised. Since the investigated doped polymers show a reversible conductivity variation as a function of water content, they are proposed as materials for humidity sensor construction.

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core-sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ~75kHz/%RH from 20 to 90%RH, ultrafast response (1s and 2s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.

Crosslinked and quaternized poly(4-vinylpyridine)/polypyrrole composite as a potential candidate for the detection of low humidity

Poly(4-vinylpyridine) was crosslinked and quaternized with 1,4-bromobutane to form a polyelectrolyte humidity sensitive film on an interdigitated gold electrode, which was further coated with a layer of polypyrrole by a facile method of vapor phase polymerization. The composite so prepared was characterized by UV-vis spectroscopy and scanning electron microscopy. The investigations on the humidity sensitive properties of the composite revealed that it exhibited an impedance as low as 10(5) Omega even at 0%RH due to the existence of intrinsic conducting polypyrrole, thus conquering the difficulties in measuring low humidity with resistive-type humidity sensors. The impedance of the composite changed linearly with humidity in the range of 0-60%RH with good sensitivity. In addition, its response time (t(90%)) for adsorption and desorption between 33% and 97%RH was estimated to be 33 s and 110 s, respectively, and a hysteresis of 5%RH was observed. All these suggest it is promising as a sensitive material for low humidity detection. The effect of concentration and ratio of oxidizing agent to doping agent, polymerization temperature of pyrrole on the humidity sensitive properties of the composite have been investigated. A sensitive mechanism of the composite was proposed by taking into account the contribution of both the intrinsic electronic conduction and ionic conduction.

Correlation between Dielectric/Organic Interface Properties and Key Electrical Parameters in PPV-based OFETs

We report on the influence of the dielectric/organic interface properties on the electrical characteristics of field-effect transistors based on polyphenylenevinylene derivatives. Through a systematic investigation of the most common dielectric surface treatments, a direct correlation of their effect on the field-effect electrical parameters, such as charge carrier mobility, On/Off current ratio, threshold voltage, and current hysteresis, has been established. It is found that the presence of OH groups at the dielectric surface, already known to act as carrier traps for electrons, decreases the hole mobility whereas it does not substantially affect the other electrical characteristics. The treatment of silicon dioxide surfaces with gas phase molecules such as octadecyltrichlorosilane and hexamethyldisilazane leads to an improvement in hole mobility as well as to a decrease in current hysteresis. The effects of a dielectric polymer layer spin coated onto silicon dioxide substrates before deposition of the semiconductor polymer can be related not only to the OH groups density but also to the interaction between the dielectric and the semiconductor molecules. Specifically, the elimination of the OH groups produces the same effect observed with hexamethyldisilazane. The hole mobility values obtained with hexamethyldisilazane and polymer dielectrics are the highest reported to date for PPV-based field-effect transistors.

A novel resistive‐type humidity sensor based on poly(p‐diethynylbenzene)

Poly(p-diethynylbenzene) (PDEB) synthesized with nickel catalyst Ni(CC○CCH)2(PPh3)2 (NiC) in dioxane–toluene mixed-solvent system at 25°C shows a rich trans structure with pendant-group (○CCH) content of about 35% having higher molecular weight and good solubility. A novel resistive-type humidity sensor based on PDEB is presented. Its humi-sensing characteristics are described and discussed. The impedance of the sensor changed from ∼ 103–107 Ω in almost the whole humidity range [∼ 15–92% relative humidity (RH)], which is low compared with sensors based on other humi-sensitive conjugate polymers, and hysteresis of no more than 3% RH was observed. The sensor prepared by Langmuir–Blodgett (LB) deposition method shows the best humidity response. An explanation of humi-sensing behavior of PDEB is attempted by taking into account the interaction between hydrogen protons and super π-conjugate orbits in PDEB.

Monochromatic‐red‐light emission of novel copolymers containing carbazole units and europium–acrylate complexes

Nearly monochromatic-red-light-emitting polymers with pendant carbazole and europium (Eu) complex were synthesized and characterized by Fourier transform infrared, elemental analysis (EA), 1H NMR, 13C NMR, UV, and gel permeation chromatography. The photoluminescence and electroluminescence (EL) properties of these polymers were investigated. A single-layer light-emitting-diode device of the structure (indium tin oxide/polymer P4/Al) was fabricated, showing the characteristic bright-red EL of the Eu3+ complex at 614 nm at a turn-on voltage of about 17 V. The EL spectrum, current–voltage, and emission-intensity–voltage characteristics of the device were measured.

Poly(propargyl alcohol) doped with sulfuric acid, a new proton conductor usable for humidity sensor construction

Abstract The electrical properties of poly(propargyl alcohol), chemically doped with sulfuric acid, were investigated as a function of the relative humidity. In the absence of water, the conductivity of the doped polymer is very low (about 3 × 10−9 S cm−1 at 25 °C) with characteristics of electronic-type charge transfer. In the presence of humidity, the charge transfer inside the polymer is mainly due to proton motion and the conductivity, ionic in character, increases with exponential trend as a function of the relative humidity. An explanation of this behaviour is attempted by taking into account the effect of water on the ion interaction. A preliminary investigation on the possibility of the use of the acid-doped poly(propargyl alcohol) as humidity sensor was also carried out.

Characterization of capacitive humidity sensors based on doped poly(propargyl-alcohol)

Films of poly(propargyl alcohol) (POHP), doped with both sulphuric acid and iron trichloride, were deposited on interdigitated gold electrodes. Their electrical properties were examined as a function of percentage relative humidity. The devices showed low-frequency capacitance linearly dependent on RH% with good response time, and are proposed as possible capacitive humidity sensors.

A novel fluorene-based cardo polyimide containing acridine for electroluminescent devices

Abstract A novel fluorene-based cardo copolyimide containing acridine (AFF10) was designed and synthesized by a one-step polycondensation of proflavine, 4,4′-(9H-fluoren-9-ylidene)bisphenylamine (FBPA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). It was characterized by FT-IR, GPC, TGA, DSC, and UV-Vis. The polyimide possessed excellent thermal stability and good solubility in low boiling solvents such as CH 2 Cl 2 , CHCl 3 , etc. The polyimide also exhibited film formability, electron/hole dipolar transporting ability and light emitting ability. The AFF10 powder emitted greenish-yellow fluorescence under irradiation of ultraviolet light. The electroluminescence properties of AFF10 were studied by fabricating and characterizing single layer electroluminescent devices (ELDs) using AFF10 as active layer. The single layer device emitted green light.