Yao-Yi Cheng

Enhancing performance of ZnO dye-sensitized solar cells by incorporation of multiwalled carbon nanotubes

A low-temperature, direct blending procedure was used to prepare composite films consisting of zinc oxide [ZnO] nanoparticles and multiwalled carbon nanotubes [MWNTs]. The mesoporous ZnO/MWNT films were fabricated into the working electrodes of dye-sensitized solar cells [DSSCs]. The pristine MWNTs were modified by an air oxidation or a mixed acid oxidation treatment before use. The mixed acid treatment resulted in the disentanglement of MWNTs and facilitated the dispersion of MWNTs in the ZnO matrix. The effects of surface property and loading of MWNTs on DSSC performance were investigated. The performance of DSSCs was found to depend greatly on the type and the amount of MWNTs incorporated. At a loading of 0.01 wt%, the acid-treated MWNTs were able to increase the power conversion efficiency of fabricated cells from 2.11% (without MWNTs) to 2.70%.

X-ray scattering and thermal analysis study of the effects of molecular weight on phase structure in blends of poly(butylene terephthalate) with polycarbonate

Blends of Poly(butylene terephthalate), PBT, with Polycarbonate, PC, were studied for a range of molecular weights and blend compositions. Blends were available in PBT/PC compositions 80/20 and 40/60, and with Mw designated by H (high) or L (low). Samples were prepared by melt crystallization, or by cold crystallization following a rapid quench from the melt. Addition of PC reduces the crystallization kinetics of PBT so that the resulting crystals are more perfect than those which form in the homopolymer. Degree of crystallinity of the blends followed the rank ordering: L/L > L/H > H/L = H/H. The glass transition behavior was investigated using dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). All blends exhibited two glass transitions at intermediate temperatures between the Tgs of the homopolymers, indicating existence of a PBT-rich phase and a PC-rich phase. Blends L/L were most, and H/H the least, miscible. Small-angle X-ray scattering was performed at room temperature on cold crystallized blends, or at elevated temperature during melt crystallization. The long period was consistently larger, and the linear stack crystallinity was consistently smaller, in blends L/L or H/L. These results indicate that in blends containing low Mw PC, there is more PC located within the PBT-rich phase. The long period was consistently smaller in cold crystallized samples, while the linear stack crystallinity was nearly the same, regardless of melt or cold crystallization treatment. Reduction of the average long period in cold crystallized samples could result from crystallization of PBT within the PC-rich phase. This is consistent with thermal analysis results, which indicate that cold crystallized samples have greater overall crystallinity than melt crystallized samples. A hypothetical liquid phase diagram is presented to explain the differences between melt and cold crystallized blends.

Miscibility, Thermal and Mechanical Properties of Melt-Mixed Poly(Lactic Acid)/Poly(Trimethylene Terephthalate) Blends

This study examined the miscibility, thermal and mechanical properties of melt-mixed blends of PLA (poly(lactic acid)) with PTT (poly(trimethylene terephthalate)). DSC and SEM results indicated that the PLA/PTT blends are immiscible. As revealed from TGA analyses, the thermal stability of the blends raises as the PTT content increases. The isothermal crystallization kinetics of the blends is analyzed using the Avrami equation in a temperature range of 190°C to 200°C. The WAXD results show that the PLA characteristic peaks take favorably shape in the cold-crystallization, and PTT form more quickly in the melt-crystallization. Nevertheless, the PTT rich blends possess lower tensile strength at yield and higher breaking elongation.

Miscibility, Mechanical and Thermal Properties of Melt-Mixed Poly(trimethylene terephthalate)/Polypropylene Blends

This study examined the miscibility, mechanical and thermal properties of melt-mixed blends of PTT(poly(trimethylene terephthalate)) with PP(isotatic polypropylene). DMA and SEM results indicated that the PTT/PP blends are immiscible. Revealed from TGA analyses, the blends with a higher PP content showed a higher degradation temperature. A complex melting behavior was observed for the blends. The isothermal crystallization kinetics of the blends was analyzed from 200°C to 210°C using the Avrami equation. The WAXD results showed that the crystal structure of PTT remained unchanged in the blends. Nevertheless, the PP rich blends possessed lower tensile strength and higher elongation at break.

Modulated differential scanning calorimetry study of blends of poly(butylene terephthalate) with polycarbonate

Abstract Modulated differential scanning calorimetry (MDSC) was used to study the glass-transition relaxation behavior in blends of poly(butylene terephthalate) (PBT), a semicrystalline polymer, with polycarbonate (PC), an amorphous polymer. Using a temperature-modulated differential scanning calorimeter (TM-DSC), a sinusoidal temperature oscillation was superimposed upon the underlying linear temperature ramp. The reversing, total, and non-reversing heat flow curves were then analyzed. We examined the efficacy of modulated differential scanning calorimeter (MDSC) to extract glass transitions (Tg) when these were covered over by rapid cold crystallization occurring in the same temperature range. Blends were available in PBT/PC compositions of 80 20 and 40 60 , and with high and low molecular weight, Mw, designated ‘H’ or ‘L’, respectively. Samples of very low initial crystallinity were prepared by rapid quenching from the melt. These samples crystallized immediately during the MDSC scan producing complex exothermic peaks when the scanning temperature increased over Tg. All blends exhibited a lower glass transition assigned to the PBT-rich phase. The upper glass transition, assigned to the PC-rich phase, was never observed in 80 H 20 L , 80 L 20 L , or 40 L 60 L . This suggests that PC-L has better miscibility with amorphous PBT, while producing a very broad, indistinct glass transition in the PC-rich phase. The Fox equation was used to determine the mass fraction composition of the two phases, and confirms that better miscibility is achieved when low molecular weight components are blended. Higher crystalline blends were prepared by melt crystallization. The size of the glass-transition step was greatly reduced in the melt crystallized blends compared to the quenched blends. Nonetheless, MDSC was used successfully to observe dual glass transitions at intermediate temperatures between the Tgs of the homopolymers for all melt crystallized blends, except 80 L 20 L . Analysis of the lower Tg indicates better amorphous phase miscibility in blends with PBT-L and PC-L; analysis of the upper Tg indicates better amorphous phase miscibility in blends with PBT-L.

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.

Low-cost X-ray conformal mask using dry film resist

A economical X-ray conformal mask manufactured by using a dry film process is reported. The dry film (HITACHI H-N650) is used as the photoresist in the photolithography process. Tin/lead and gold were electroplated as the X-ray absorber. The feasibility and limitations of the dry film process were addressed. Using this X-ray conformal mask in X-ray lithography, 1000 μm thick PMMA microstructures were achieved to demonstrate the fidelity of this method.

Comparison of Polyimide Composites with Non-covalent Modified and Acid Modified Multi-wall Carbon Nanotube

In this study, it was attempted to increase the electrical conductivity of polyimide (PI) by adding multi-wall carbon nanotubes (MWNT), mainly because the high aspect ratio carbon nanotubes can reduce resistance and enhance antistatic ability to meet electrostatic charge (ESC) criteria of polymer hybrid films. MWNT were modified successfully with a sodium salt of 6-aminohexanoic acid (Na-AHA), which has been verified by FTIR and TEM observations. During the blending process, the PI/MWNT composites thus produced were compared with unmodified MWNT to study the miscibility and interaction among the components. The homogeneous dispersion of the non-covalently modified MWNT (Na-AHA-CNT) promoted the thermal and electrical conductivity properties of PI composite films. The results are compared with those of PI composites with acid-modified and unmodified MWNT.

ADHESION OF PET/PSMA INTERFACES REINFORCED WITH PLASMA TREATMENT

The interface between biaxially oriented poly (ethylene terephthalate) (PET) films and poly (styrene-co-maleic anhydride) (PSMA) was reinforced by nitrogen plasma treatment of PET film and subsequent annealing treatment of the PET/PSMA bi-material. The fracture toughness, Gc, of the interface was quantitatively measured using an asymmetric double cantilever beam test (ADCB). X-ray photoelectron spectrometry (XPS) was used to measure the change in the surface composition of PET films upon plasma treatment and correlate the fracture toughness of the interface. The fracture energy of PET/PSMA interface is significantly enhanced by annealing the plasma treated PET with PSMA at a temperature greater than the glass transition temperature of PSMA (~ 120°C). At an annealing temperature of 150°C, Gc increases with increasing plasma treatment time and reaches a plateau value of ~ 100–120 J/m2, a two order of magnitude increase in Gc compared with that of samples annealed at 130°C. The enhancement of the adhesion is resulted from the in-situ formation of copolymers due to reaction between amine functional groups from the plasma treatment and anhydride groups from PSMA. For plasma treatment time

Preparation and Characterization of Porous Hydrogen Silsesquioxane by Sol-Gel Process

This paper presents study on porous Hydrogen Silsesquioxane (HSQ) of dielectric constant near 2. Porous HSQ solution was spin-on coated and then treated by wet ammonia. During the treatment, HSQ film went through a sol-gel process. Pores were uniformly formed in HSQ film after a baking process to remove solvent. A solid network structure of porous HSQ was then formed after a high-temperature curing process. In this work, we compared the properties of porous HSQ with varying process time of wet ammonia treatment and curing temperature. Change of chemical structure was analyzed by Fourier transform infrared (FTIR) spectrometry. We found that the cage structure of porous HSQ was reduced but the network structure was enhanced as treatment time of wet ammonia increased. Hardness and Young’s modulus were measured by nano-indentation technique. The adhesion strength of porous HSQ with silicon carbide was measured. Surface properties and electrical characterization of porous HSQ with varying process conditions have also been examined.