Syang-Peng Rwei

Fullerene bisadduct as an effective phase-separation inhibitor in preparing poly(3-hexylthiophene)–[6,6]-phenyl-C61-butyric acid methyl ester blends with highly stable morphology

This work demonstrates that the bis-adduct of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is an effective inhibitor of the aggregation of PCBM inside the poly(3-hexylthiophene) (P3HT) matrix. Substituting some of the PCBM with bis-PCBM apparently reduces the size of PCBM-rich clusters, enhancing both the short-circuit current density (JSC) and the fill factor (FF), leading to a ∼17% increment in power conversion efficiency (PCE) for a cell with 8.3 wt% bis-PCBM replacement. More importantly, a tiny amount of bis-PCBM significantly improves the morphological stability of P3HT–PCBM blend against high-temperature aging. All P3HT–PCBM:bis-PCBM devices exhibit extremely stable PCEs, which do not visibly change upon heating at 150 °C for 15 hours.

[60]Fulleropyrrolidines Bearing π-Conjugated Moiety for Polymer Solar Cells: Contribution of the Chromophoric Substituent on C60 to the Photocurrent

Two fullerene-terthiophene dyads without hexyl chains (3T-C₆₀) and with hexyl chains (3TH-C₆₀) on the terthiophene substituent are synthesized by 1,3-dipolar cycloaddition of corresponding azomethine ylides to C₆₀. The cyclic voltammetry studies indicate no apparent electronic communication between the terthiophene pendent group and the fulleropyrrolidine core in the ground state. However, a significant florescence quenching is observed for 3T-C₆₀ and 3TH-C₆₀, compared to their fluorescent terthiophene (3T) and 3TH precursors, respectively, suggesting the occurrence of strong intramolecular electron/energy transfers in the photoexcited state. Furthermore, these new fulleropyrrolidine derivatives are applied as electron acceptors to fabricate poly(3-hexylthiophene) (P3HT) based bulk heterojunction solar cells. The incident photon-to-current efficiency (IPCE) value of the P3HT/3T-C₆₀ device is significantly higher than that of the P3HT/PCBM cell in wavelengths of 350-420 nm. This finding provides direct evidence for the contribution of 3T excitons to the photocurrent. Replacing 3T-C₆₀ with 3TH-C₆₀ effectively improves the morphology of the photoactive layer and widens the window of optimal D/A ratios, raising the power conversion efficiency (PCE) from 2.14% to 2.54%. Importantly, these devices exhibit superior stability of PCE against high-temperature aging.

Electrospinning PVA solution-rheology and morphology analyses

This study investigates the electrospinning (ES) of poly(vinyl alcohol) (PVA). All of the electrospinning process or property parameters, including the concentration effect, the molecular weight effect, the pH effect, the salt effect, electrode voltage, surface tension, shear viscosity and extensional viscosity were examined. The pH variation had an insignificant effect on the formation of fibers. An increase in electrode voltage and salt concentration negatively affects the ES process. The salt concentration that yields an acceptable ES membrane without droplets was below 0.001 N. Also, the decrease in elongation viscosity rather than the variation in electric conductivity or surface tension was the main cause of the negative effect on the fiber formation when the salt was added to a PVA solution. The salt negative effects follow the order CaCl2 < NaCl < NaI < KBr < KI. Experimental results show that the ES processability of PVA solution depends mainly on the concentration and secondly on the molecular weight of the dissolved polymer. The PVA solution prepared with a larger molecular weight had a lower concentration window in the ES process. The concentration window of PVA solution with an MW of 88,000 in the ES process ranged between 6 and 14 wt%. Additionally, experimental results demonstrated that the upper limitation on PVA concentration depends strongly on the extension viscosity of the spun solution. Whenever the power law index n determined by extension test exceeds one, spinning is unfeasible, regardless of whether the index of the power law for shearing is within the normal range. Briefly, this work indicates that the extension viscosity can be adopted as a good indicator for predicting ES processability.

Preparation of thermo- and pH-responsive star copolymers via ATRP and its use in drug release application

A star-shaped copolymer, poly(N-isopropylacrylamide-co-itaconamic acid (poly(NIPAAm-co-IAM)), being pH- and thermo-dual-responsive, was synthesized by atomic transfer radical polymerization (ATRP) and characterized in this work. The lower critical solution temperature (LCST) of the star copolymer increases with the molar fraction of IAM. The particle size decreases as the temperature increases but increases as the pH value increases. Transmission electron microscopy (TEM) reveals that the star-shaped copolymer has a near-spherical core-shell structure that favors drug delivery. The star copolymer can be used in drug encapsulation as well as drug release. The star copolymer has different drug release rates in environments of different pH, and thus it can carry drugs in an acidic (gastric) environment and release the drugs in a neutral or less acidic (intestinal) environment.

Electrochemical determination of morin in Kiwi and Strawberry fruit samples using vanadium pentoxide nano-flakes

Herein, we report the synthesis of Vanadium Pentoxide Nanoflakes (V2O5 NF) using ionic liquid and employed the V2O5 NF in electrochemical determination of Morin (MR) in fruit samples. The V2O5 NF were characterized by Powder X-ray diffraction (PXRD), scanning electron microscope (SEM), energy-dispersive X-ray analyzer (EDX), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). Remarkably, the as-synthesized V2O5 NF exhibited excellent electrochemical behavior and electrochemical ability towards MR. The CV and DPV studies were recognized that the electrochemical performance of V2O5 NF film modified glassy carbon electrode (V2O5 NF/GCE) towards detection of MR is outstanding in comparison with unmodified GCE. The proposed MR sensor shows a wide linear range, high sensitivity, and low limit of detection are 0.05-10.93μm, 1.130μAμM-1cm-2, and 9nM respectively. The fabulous analytical parameters of the developed sensor surpassed the previously reported modified electrodes, rendering the potential application of V2O5 NF in environmental, biomedical, and pharmaceutical samples.

Terthiophene–C60 dyads as donor/acceptor compatibilizers for developing highly stable P3HT/PCBM bulk heterojunction solar cells

Forming nano-scale interpenetrating networks in electron donor/acceptor blends via phase-separation tuning and maintaining their optimal morphology are of paramount importance for the favorable performance and operational lifetime of bulk heterojunction (BHJ) polymer solar cells. In this work, two fulleropyrrolidine derivatives that bear π-conjugated terthiophene (3T) and two hexyl (H) or ethylhexyl (EH) chains, abbreviated as 3T-H-C60 and 3T-EH-C60, are separately used as a compatibilizer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The effect of the loading of such an agent on the photovoltaic properties of solar devices and the morphological stability of the P3HT/PCBM blend was examined. The substitution of PCBM with a tiny amount of 3T-H-C60 or 3T-EH-C60 apparently enhances the short-circuit current density, reflecting the formation of small PCBM clusters within the P3HT matrix. More importantly, optical microscopy, transmission electron microscopy and photoluminescence measurements verify that the presence of 1 wt% 3T-H-C60 or 3 wt% 3T-EH-C60 effectively hinders the thermal motion of PCBM molecules to form micro-scale clusters, leading to an extremely stable morphology even under long-term exposure to elevated temperatures. Accordingly, the power conversion efficiencies of P3HT/PCBM:3T-H-C60 and P3HT/PCBM:3T-EH-C60 devices remain very steady during prolonged aging at 130 °C. This work provides valuable guidelines for the design of an effective compatibilizer for thermally stable polymer/fullerene BHJ solar cells.

Fluid Simulation of the Airflow in Texturing Jets

This study attempts to understand flow behavior inside texturing nozzles by computer simulation. The texturing degree and fluctuation number are calculated for different texturing conditions while processing fine denier yarn thread. Simulation results indicate that texturing is enhanced when the cross-sectional area of the inlet hole reaches 1/4, or when the ratio of the length over diameter (L/D) of the yarn channel is between 8 and 10. Additionally, the obliqueness of the air inlet hole with an angle between 45° and 60° facilitates texturing. A yarn channel with a noncircular cross section outperforms one with circular cross section. Finally, a yarn channel with a 10° divergent exit can benefit texturing. All these results are compared with the experimental observations of other researchers or with satisfactory industrial nozzles, and there is good agreement.

Fluid Simulation of the Airflow in Interlacing Nozzles

The airflow in interlacing nozzles is simulated on a computer to understand flow behavior inside the nozzle. The interlacing degree and loop frequency of the airflow are calculated with respect to different interlacing conditions while processing fine denier yarn thread. The results reveal that better interlacing is produced when the cross-sectional area of the inlet hole or the length of the yarn channel decreases or the inlet air pressure increases. A yarn channel with a round cross section outperforms other shapes. In addition, neither the divergent nor the seriously convergent exit provides any positive effect, except that a modest convergence might somewhat enhance interlacing. Finally, a slight obliqueness or tangential air inlet hole insertion favors the interlacing process. All these results are compared with the experimental observations by other researchers and good agreement is found.

Synthesis and viscoelastic characterization of sulfonated chitosan solutions

In this study, sulfonated chitosan (SCS) with a water-soluble property was synthesized and rheologically characterized. The Maxwell Model can accurately describe a regular chitosan (CS) solution. The G′, G″ crossover shifted toward lower frequencies as the CS concentration increased, revealing an increase of relaxation time. A frequency–concentration superposition master curve of CS solution was therefore plotted and well fitted by the experiment result. However, a modified Maxwell Model, which captures the occurrence of the quasi-plateau region of G′ in the low-frequency range, representing the initially falsely connected structure between the sulfonic acid groups and the protonated ammonium groups, was proposed for the SCS solution. The crossover of G′ and G″ was found to be independent of the SCS concentration, indicating its lower molecular weight yields a high overlap concentration, Ce. The rheological properties of SCS solutions can be affected as the following factors are increased in the order of declining effect; pH level > temperature > salt concentration.

Sol/gel transition of chitosan solutions

This work studies the occurrence of sol/gel transition and the gel rheology for chitosan solution under various conditions. Experiments were conducted in an oscillatory shear apparatus with small amplitude, using a Rheometrics SR-5 rheometer, with Couette and parallel plate geometries. The experimental results demonstrate that the sol/gel transition concentration and the elastic modulus (G′) for CS gel decrease as the pH value and the molecular weight (M w) increase. However, the sol/gel transition concentration and G′ became independent of M w when M w exceeded a threshold. The higher ionization constant, K p, is responsible for the higher sol/gel transition concentration in a formic acid solution than in an acetic acid solution with equivalent molar concentration. The elastic modulus G′ of a CS gel increases with temperature, which relationship differs from that for many polysaccharides, and can be understood through classical rubber elastic theory. Finally, a gel whose concentration was barely above the sol/gel point exhibited aging, and its G′ and G″ declined rather than increase with time, accompanied by a reversal from the sol/gel state back to the sol state. This is an uncommon aging behavior for a polysaccharide and a detailed explanation is provided.