Kuo-Huang Hsieh

Cesium carbonate as a functional interlayer for polymer photovoltaic devices

The device characteristics of polymer solar cells with cesium carbonate (Cs2CO3) as an electron-injection interlayer have been investigated. It is found that the insertion of Cs2CO3 at the cathode interface improves the device power conversion efficiency from 2.3% to 3.1%. In order to further understand the mechanism, the interfacial interaction between the active organic layer and the cathode was studied by x-ray photoemission spectroscopy (XPS). The results of XPS measurement indicate the fact that a portion of electrons transfer from the interlayer into the organic layer, resulting in n-type doping. The n-doping effect enhances the efficiency of electron injection and collection. Further, the maximum open-circuit voltage (Voc) was determined from its temperature dependence. For the device with Cs2CO3, the maximum Voc is extremely close to the corresponding value of the energy difference between the highest occupied molecular orbital of the electron donor and the lowest unoccupied molecular orbital of t...

Antibacterial activity and biocompatibility of a chitosan–γ-poly(glutamic acid) polyelectrolyte complex hydrogel

In this study, we prepared a polyelectrolyte complex (PEC) hydrogel comprising chitosan as the cationic polyelectrolyte and gamma-poly(glutamic acid) (gamma-PGA) as the anionic polyelectrolyte. Fourier transform infrared spectroscopy revealed that ionic complex interactions existed in the chitosan-gamma-PGA PEC hydrogels. The compressive modulus increased upon increasing the degree of complex formation in the chitosan-gamma-PGA PEC hydrogel; the water uptake decreased upon increasing the degree of complex formation. At the same degree of complex formation, the compressive modulus was larger for the chitosan-dominated PEC hydrogels; the water uptake was larger for the gamma-PGA-dominated ones. Scanning electron microscopy images revealed the existence of interconnected porous structures (pore size: 30-100mum) in all of the chitosan-gamma-PGA PEC hydrogels. The chitosan-gamma-PGA PEC hydrogels also exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. In addition, in vitro cell culturing of 3T3 fibroblasts revealed that all the chitosan-gamma-PGA PEC hydrogels were effective in promoting cell proliferation, especially the positively charged ones (chitosan-dominated). Therefore, the chitosan-gamma-PGA polyelectrolyte hydrogel appears to have potential as a new material for biomedical applications.

Damping properties of interpenetrating polymer networks of polyurethane-modified epoxy and polyurethanes

Interpenetrating polymer networks (IPNs) were prepared from polyurethane (PU)-modified epoxy with different molecular weight of polyol and polyurethanes based on the mixture of polydiol and polytriol by a one-shot method. Two types of PU-modified epoxy: PU-crosslinked epoxy and PU-dangled epoxy were synthesized, and the effects of the different molecular weights of polyol in the PU-modified epoxy/PU IPNs on the dynamic mechanical properties, morphology, and damping behavior were investigated. The results show that the damping ability is enhanced through the introduction of PU-modified epoxy into the PU matrix to form the IPN structure. As the molecular weight of polyol in PU-modified epoxy increases, the loss area (LA) of the two types of the IPNs increases. PU-dangled epoxy/PU IPNs exhibit much higher damping property than that of the PU-crosslinked epoxy/PU IPNs with 20 wt % of PU-crosslinked epoxy.

Graft interpenetrating polymer networks of urethane-modified bismaleimide and epoxy (I): mechanical behavior and morphology

Polyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)] polyols are employed as a graft agent to prepare interpenetrating polymer networks of urethane-modified bismaleimide (UBMI) and the diglycidyl ether of bisphenol A (Ep) (UBMI/Ep graft-IPNs). The UBMI is introduced and partially grafted to the epoxy by PU graft agents, and then simultaneous bulk polymerization technique is used to prepare the graft-IPNs. All the PU graft agents were characterized by infrared (IR). The tensile strength of both the UBMI/Ep graft-IPNs with PU(PBA) and PU(PPG) graft agent systems increased to a maximum value with increasing UBMI content in the system and then decreased with further increasing the UBMI content. For both kinds of PU with various molecular weight in the UBMI/Ep graft-IPNs, the Izod impact strength increased with the UBMI contents increasing. The better compatibility of PU(PBA)-based UBMI/Ep graft-IPNs led to higher impact strength. On the contrary, the fracture energy (GIC value) of the resultant UBMI/Ep graft-IPN showed that the UBMI/Ep graft-IPN with PU(PPG) graft agent had much higher GIC value than that with PU(PBA) graft agent. The morphology of this IPN with PU(PBA) graft agent exhibited a homogeneous one-phase system, while the UBMI/Ep graft-IPN with PU(PPG) graft agent showed a two-phase morphology with the UBMI particles dispersed in the epoxy matrix.

Interpenetrating polymer networks of polyaniline and maleimide-terminated polyurethanes

Abstract A series of novel conducting interpenetrating polymer networks (IPNs) was prepared by sequential polymerization of maleimide-terminated Polyurethane (UBMI) and polyaniline (PANI) which was doped with dodecylbenzenesulfonic acid (PANIDB). From the differential scanning calorimetry (DSC) analysis of the IPNs, the compatibility of the polyether-type UBMI with PANIDB was better than that of the polyester-type UBMI with PANIDB. The IPNs exhibited higher conductivity and better mechanical properties when the polyether-type UBMIs were used in the composition. The scanning electron microscopy (SEM) of the IPNs illustrated heterogeneous structure of the cured resins when the polyester-type UBMI was incorporated in the UBMI/PANIDB IPNs. Scanning tunneling microscopy (STM) images of the compatible polyether-type PANIDB /UBMI IPNs indicated that the conducting region of the PANIDB was distributed as continuous conducting networks in the matrix, which resulted in higher conductivity and very low threshold concentration of the PANIDB for the conducting IPNs.

Polyurethane-based conducting polymer blends: I. Effect of chain extender

Polyurethane (PU) with (m-phenylene 4-diaminosulfonic acid: PDSA) as chain extender can deeply influence the properties of its blending with n-dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PADB) The sulfonic chain extender (PDSA) provides an additional probability of creating H-bonding with PADB molecules which can be characterized by IR-spectra. In the presence of intermolecular H-bonding, the conductivity and tensile strength of the PADB/PU blends can be changed, especially when the conducting PADB forms a continuous phase in the matrix at high PADB composition. Thermal analysis also reveals variation of glass transition points of the blends at various composition due to the interaction and different degree of miscibility. Scanning electronic microscopy (SEM) pictures of the blends demonstrate a more deformed type of morphology when PDBA is used as a chain extender in the preparation of PU.

Interpenetrating polymer networks of bismaleimide and polyurethane-crosslinked epoxy

This study prepared an interpenetrating polymer network of bismaleimide and polybutylene adipate-based polyurethane-crosslinked epoxy (BMI/PU-EP IPN) using the simultaneous bulk polymerization technique. Infrared spectra analysis was also performed to identify the polyurethane-crosslinked epoxy (PU-EP). Also investigated herein were the mechanical properties including tensile strength, fracture energy, and Izod impact strength of various bismaleimide content in PU-EP matrix. In addition, differential scanning calorimetry and thermogravimetric analyses of the BMI/PU-EP IPN were conducted as well. Analyses results demonstrate that the bismaleimide was dissolved primarily in the polyurethane domains of the epoxy matrix to form a compatible system, thereby increasing the mechanical strength of the BMI/PU-EP IPNs.

Interpenetrating polymer networks of 2-hydroxyethyl methacrylate terminated polyurethanes and polyurethanes

Interpenetrating polymer networks (IPNs) of 2-hydroxyethyl methacrylate terminated polyurethanes (HPU) and polyurethanes (PU) with different ether-type polyols were prepared by simultaneous solution polymerization. Differential scanning calorimetry showed that the compatibility of polymers in IPN formation depends on the molecular weight of the prepolymers. Compatible IPN systems resulted in greater-than-average density values and reduced swelling behaviour. Water absorption of the IPNs was found to be mainly determined by the hard-to-soft segment ratio of the materials. The maximum tensile modulus occurred at a 25 wt% HPU content for the compatible systems and a 12.5 wt% HPU content for those that were incompatible. The maximum tensile strength occurred at a 25 wt% HPU content for all the IPN systems. Morphological observations using a scanning electron microscope revealed different fracture surfaces between the compatible and incompatible systems.

Kinetic study of acid depolymerization of chitosan and effects of low molecular weight chitosan on erythrocyte rouleaux formation.

In this study, the depolymerization of chitosan was carried out in an acetic acid aqueous solution and was followed by viscometry for molecular weight determination. It was found that the depolymerization rate increased with elevated temperatures and with high acid concentrations. Based on FTIR analysis, the chitosan was depolymerized randomly along the backbone; no other structural change was observed during the acid depolymerization process. Revealed in the TGA study, the degradation temperature and char yield of LMWCs (low molecular weight chitosan) were molecular weight dependent. The blood compatibility of LMWCs was also investigated: rouleaux formation was observed when erythrocyte contacted with LMWCs, which showed that LMWCs are able to interfere with the negatively charged cell membrane through its polycationic properties. Furthermore, as regards a kinetics investigation, the values of M(n) (number-average molecular weight) were obtained from an experimentally determined relationship. The kinetics study showed that the complex salt, formed by amine on chitosan and acetic acid, acted as catalyst. Finally, the activation energy for the hydrolysis of the glycosidic linkage on chitosan was calculated to be 40kJ/mol; the mechanism of acid depolymerization is proposed. In summary, LMWCs could be easily and numerously generated with acid depolymerization for further biological applications.

Fast fabrication of integrated surface-relief and particle-diffusing plastic diffuser by use of a hybrid extrusion roller embossing process.

Most plastic diffusers are either of surface-relief or particle-diffusing types, based on different principles and fabrication methods. This paper reports an innovative extrusion roller embossing process, which enables the fabrication of diffusers with both surface-relief and particle-diffusing functions. An extruder with die is employed to fabricate the thin film of PC/bead composite; the roller micro-embossing process is used to replicate the microstructure onto the surface of PC composite film. A metallic roller mold with microstructures is fabricated using turning process. During the extrusion rolling embossing process, the extruded film of PC with diffusion beads is immediately pressed against the surface of the roller mold. Under the proper processing parameters, the plastic diffusers integrating surface-relief and particle-diffusing functions have been successfully fabricated. The shape, uniformity, and optical properties of fabricated diffuser have been verified. This method shows the great potential for continuous fabrication of high-performance plastic diffusers integrating surface-relief and particle-diffusing functions with high throughput.