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The physical properties of rubber compounds are mainly determined by the filler dispersion within the rubber matrix, filler–rubber interaction, and chemical crosslink structure caused by sulfur. Carbon black or silica is typically used as a reinforcing filler in tire tread compounds; however, binary filler systems comprising the two types of filler are also currently being used to complement each other. This study used binary filler systems to manufacture vulcanizates and classified the vulcanizate structures as chemical crosslinks caused by sulfur, physical crosslinks caused by carbon black (carbon black–bound rubber), and silica–silane–rubber networks caused by silica and silane. The effect of each vulcanizate structure on the physical properties was also calculated. In the proposed binary filler system, silica chemically bonds with rubber molecules, unlike carbon black. Therefore, the crosslink density per unit of silica content was 19% higher than that of carbon black, in which rubber molecules were physically adsorbed on the surface. Tensile properties affected by 1 unit of crosslinking density for each filler were calculated, and silica was found to contribute more in the low-elongation range, whereas carbon black contributed more in the high-elongation range. Regarding tan δ at 60 °C and abrasion resistance per unit crosslink density of filler, carbon black made a greater contribution than silica, whereas silica had a greater contribution to wet traction and snow traction.

Low molecular O-carboxymethyl chitosan, a derivative of chitosan, was conjugated with a hydrophilic carboxymethyl group, following which the conjugate was modified with a furfuryl group. The chitosan derivative was cross-linked to encapsulate a model protein, bovine serum albumin (BSA), in the presence of Rose Bengal under visible light irradiation. The encapsulated BSA was slowly released from the matrix over 2 weeks. The modified chitosan exhibited antimicrobial activity and was non-cytotoxic to NIH3T3 fibroblasts. The wound healing effect of the cross-linked chitosan derivative was examined in Sprague-Dawley rats at 3, 7, and 14 days post-wounding. Cross-linked and murine epidermal growth factor (mEGF)-encapsulated chitosan derivatives healed wounds more rapidly in rats than non-encapsulated mEGF or chitosan derivative alone. Thus, visible light-curable chitosan has good potential for application as wound-healing matrix.

To photo-immobilize bone morphogenetic protein-2 (BMP-2), UV light-reactive gelatin (azidophenyl gelatin, Az-gel), which is introduced with an N-(4-azidobenzoyloxy) succinimide-containing an azide group, was prepared as a carrier of BMP-2. Characterization of the photo-reactivity of Az-gel was evaluated by the curing ratio and it was micropatterned using a photomask. The cross-linking ratio and an enzyme-linked immunosorbent assay, enzymelinked immunospecific assay (ELISA)-based BMP-2-release test were used to determine the optimal density of Azgel (1, 3, and 5%) and UV treatment time (10, 30, 60 s) of the BMP-2 carrier in collagen matrix. The results showed that 5% Az-gel with 60 s of UV treatment was the most efficient condition for cross-linking. Cytotoxicity assays using the C2C12 mouse myoblast cell line showed that there were no cytotoxic effects of Az-gel. Alkaline phosphatase activity and calcium ion detection assays to evaluate the osteoinductive activities were conducted in assumed optimal condition of Az-gel (5% and 60 s UV treatment) 14 days post-treatment. In our study, the osteoinductive activities were the highest in cells treated with BMP-2 and the photo-reactive Az-gel carrier compared to BMP-2 alone or untreated control cells in collagen matrix at all time points (3, 7, and 14 days).

A photoreactive azidophenyl hyaluronic acid (Az-HA) derivative for tissue augmentation was prepared by direct amide bond formation between the carboxyl groups of HA and the amine groups of 4-azidoaniline. 4-Azidoaniline was introduced to the carboxyl group of hyaluronic acid that was activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). The prepared Az-HA derivative was characterized by 1H NMR to measure the degree of modification. The Az-HA derivative was photo-cross-linked with varying UV irradiation times. Az-HA-20 hydrogels were formulated into injectable gels for soft tissue augmentation. The morphology, equilibrium swelling, rheological property, and in vitro degradation of hydrogels were examined. The cell cytotoxicity test of the Az-HA derivative was also examined. Az-HA-20 formed stronger hydrogels with higher storage modulus (Pa’) as UV irradiation time increased. Also, the in vitro degradation rate was lower as UV irradiation time increased. This study demonstrates that Az-HA-20 hydrogels have potential for use as injectable, biodegradable, and biocompatible hydrogels for tissue augmentation.

Titanium and its alloys have been used for a wide range of dental implant materials because of their biocompatible properties. Due to the osseointegration between the bone and implant surface that is required after implantation surgery, surface modification of titanium has been investigated. Even though bone morphogenetic protein-2 (BMP-2) and other growth factors have been applied to increase the efficiency of osseointegration, their short half-life has been a disadvantage. In this study, BMP-2 was photo-immobilized on a titanium surface using azidophenyl hyaluronic acid (Az-HA) as a matrix, and C2C12 cell lines were cultured on the modified surface. The photoreactive azidophenyl hyaluronic acid was prepared and characterized in a previous report. To demonstrate the osteoinductive effect of the photo-immobilized BMPs, alkaline phosphatase (ALP) activity assay, calcium detection assay, and alizarin red staining were conducted. Open image in new window

Carboxymethyl starch was modified by the incorporation of an azidophenyl group to prepare photoreactive starch, and characterized by Fourier transform infrared reflectance (FT-IR), proton nuclear magnetic resonance (1H-NMR), and ultraviolet (UV) spectroscopy. Photo-irradiation immobilized the Az-starch on a polystyrene plate and it was stably retained on the surface. The protein containing immobilized Az-starch was also immobilized on a stripe micropatterned plate. UV irradiation time and Az-starch concentration were used to alter the physical properties of Az-starch and consequently control the rate of epidermal growth factor (EGF) release. The Az-starch that released growth factor was not cytotoxic to 3T3-L1 fibroblast cells, and the immobilized EGF maintained its activity and induced cellular proliferation in vitro. These results suggest that Az-starch could be useful as a clinical synthetic material for medical applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Titanium (Ti) is widely used as an implant material. There are various kinds of Ti surface modification methods to facilitate effective osseointegration. In this study, UV-curable azido-LMC (azidophenyl low molecular weight chitosan) was used to modify the Ti surface. Here we suggest a novel Ti coating material that confers complex, diverse improvements to the Ti surface through a simple process. First, a cytotoxicity test of azido-LMC against osteoblast MG-63 was performed. The curing ratio dependent on UV irradiation time and concentration was determined by a comparison of weight. A 5% azido-LMC solution, which showed a wide curing ratio range, was used to investigate the surface properties. The contact angle value was measured to compare hydrophilicity, and osteoblast MG-63 cells were cultured on the coating surface. The Bradford assay was used to assess the protein immobilization capability. Hydroxyapatite, which has a beneficial influence on osseointegration, was included on the coating surface and observed by scanning electron microscopy. Surface roughness was measured by atomic force microscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Adhesions occurring on a variety tissues and operation sites are a serious side effect of surgery and may require additional surgery for removal. Therefore, Furfuryl-fish gelatin (F-f.gel) was synthesized by introducing a furan ring to fish gelatin for application as an anti-adhesion agent. F-f.gel was cured by visible-light irradiation, which changed the material from a solution to a film. The prepared F-f.gel was characterized by proton nuclear mag- netic resonance spectroscopy ( 1 H NMR), substitution ratio, gel permeation chromatography (GPC), methyl thiazolyl tetrazolium (MTT) assay, and tests for measuring photo immobilization, water contact angle (WCA), and cell attach- ment. The results showed that F-f.gel was effective as an anti-adhesion agent.

The retention behavior of star-shaped polystyrene (PS) at the liquid chromatographic critical condition of linear PS was investigated. The star-shaped PS samples were prepared by anionic polymerization of styrene and subsequent linking of the polystyryl anions with divinylbenzene. The linking reaction yields a series of star-shaped PS with different number of branches of equal length. Three star-shaped PS samples with different arm molecular weight (MW) were prepared. To investigate the MW (hence the branch number) dependence of the LCCC (liquid chromatography at the critical condition) retention, the two-dimensional liquid chromatography method was used—first separating the polymers with respect to the molecular weight and subsequently separating the effluent by LCCC. Two different pore size columns were used for the LCCC separation to investigate the pore size dependence. The LCCC retention shows a very complex behavior. The retention time of the star-shaped PS shows a strong variation with MW (branch n...

The incremental addition of divinylbenzene was used to generate star polystyrenes in a nearly full conversion of a living polystyrenyl anion. The dramatic increase in the molecular weight of the star polystyrenes with a limited supply of the living polystyrene supported the formation of gradient-star polystyrenes through star-star coupling. The stoichiometric analysis of the star polymers revealed that their connection polymer had a shorter length than their branch polymer. The measured solution viscosity of the gradient-star polymers greatly deviated from a linear correlation with the molecular weight and was in parallel to a theoretical simulation based on a highly branched structure of the gradient-star polymer.

Star polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental-addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one-shot addition.

The effects of the indium flow rate on the properties of InGaN/GaN quantum wells have been investigated by using atomic force microscopy, photoluminescence (PL), transmission electron microscopy and high-resolution x-ray diffraction. The high-indium content InxGa1?x N/GaN (x > 0.3) quantum wells used in this study were grown on c-plane sapphire by using metal?organic chemical vapour deposition. The indium flow rate in the quantum well layers was varied while keeping other growth parameters fixed. With increasing indium flow rate, the indium solid composition in the well layers increases and the magnitudes of the indium spatial fluctuations increase. However, the defects increase and the quantum well structure degrades. As a result, the PL peak position was redshifted and the intensity was reduced. The transmission electron microscopy images show that the quantum-dot-like regions are clear for InxGa1?x N/GaN (x = 0.35). Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. In addition, the electroluminescence spectra of the light emitting diode shows that the dominant mechanism in InGaN/GaN quantum wells is a localized effect in the quantum-dot-like regions. The V-defects originate at threading dislocations and the inversion domain boundary due to higher misfit strain with increasing indium flow rate.

We have prepared high-quality In0.3Ga0.7N/GaN quantum wells (QWs) by metallorganic chemical vapour deposition and investigated their optical and structural properties using photoluminescence (PL), high-resolution x-ray diffraction (HRXRD) and cross-section and high-resolution transmission electron microscopy measurements. Growth parameters of the QWs were determined by adjusting the PL peak at around 2.7 eV (460 nm). PL peak intensity increases with the barrier thickness and then saturates and shows maxima when the number of wells is five or six in the In0.3Ga0.7N/GaN QWs. The results of transmission electron microscopy, PL and HRXRD show that the growth rate of the QW and barrier does not change with increasing number of wells in samples grown under optimum growth conditions, i.e. the period (well and barrier) thickness is constant. Based on the measurements of high-resolution transmission electron microscopy and temperature- and excitation-power-dependent PL, the dominant luminescent centre of In0.3Ga0.7N/GaN QWs is a quantum-dot-like localized state.

The photoelectric transient process of a 99 period Si0.823 Ge0.177 (17 A)/Si(24 A) superlattice (SL) was investigated by the photocurrent decay (PCD) method. Decay lifetimes of electrons and holes in SL and Si capping layers are extracted from the transient intensity and polarity of the PCD signal. The temperature and bias dependences of lifetime exhibit the thermal activation of heavy holes, the dissociation of free excitons and the thermal activations of shallow and deep levels. The heavy holes hop in and out of the well at low temperature and weak electric field, while they jump over the well region in a strong electric field or at high temperature. Lifetimes of electrons and holes are nearly the same in the Si capping layer, while the lifetime of holes is about one order of magnitude longer than that of electrons in the SL, mainly due to the quantum confinement of holes in the SL region.

Chlorofluorinated polyimides were prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 2,2′-dichloro-4,4′-diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near-IR region were also investigated. Rib-type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 107–112, 1999

We have investigated the doping characteristics of Mg doped GaN films grown by metalorganic chemical vapor deposition. We have found that Mg doped GaN layer shows high electrical conductivity and good surface morphology, simultaneously, when the [Mg]/[Ga] ratio in gas phase is 7.6×10−3. If [Mg]/[Ga] ratios exceed an optimum value of 7.6×10−3, surface morphologies and electrical conduction properties become poor and blue emissions, considered as deep donor-to-acceptor-pair transitions in photoluminescence spectra, are dominant. Moreover, the Mg–Si codoping characteristics was explained effectively taking advantage of the concept of competitive adsorption between Mg and Si during the growth. Based on the experimental results, we suggest the methods to get a p-GaN showing high conductivity using Mg-Si codoping.

The origin of the radiative recombination leading to yellow luminescence (YL) has been elucidated by the study of luminescence properties of GaN films grown with two different gas feeding methods. GaN films were grown on a (0001) sapphire substrate in a rapid thermal chemical vapor deposition (RTCVD) reactor. GaN films emitted two different luminescence energies, 2.2 and 3.47 eV, depending on the introducing position of hydrogen gas in the growth reactor. The distribution of the TMGa flow and gas phase reactions in the reactor were investigated to understand the effect of the gas feeding methods on the optical properties of GaN films. The results suggest that YL is related to Ga vacancies in the grown films.

The material qualities of GaN overlayers grown on (0001) sapphire substrates by metal-organic chemical vapour deposition were investigated as a function of nitridation time. The nitridation of sapphire surface notably affects on the properties of the GaN overlayers, such as surface morphology and structural, optical and electrical properties. The GaN overlayer with a short nitridation time of 30 s shows a good surface morphology, a relatively low background Hall carrier concentration and a high electron mobility, but the defect-related emission around 550 nm increased. Furthermore, for the GaN overlayer with nitridation for 180 s, even though it has a low (102) full width at half-maximum of the high-resolution x-ray diffraction rocking curve, other material properties were degraded owing to the long nitridation time. It was found that material properties have a trade-off relationship with the variation of nitridation time.

The effects of growth parameters have been examined for the epitaxial growth of a void-free SiC film on a Si substrate. Experiments were performed under various growth conditions by pyrolyzing tetramethylsilane (TMS) in a rapid thermal chemical vapor deposition reactor. Void-free single crystalline SiC films were grown when the Si substrate was heated after the flow of TMS. The increase of TMS flow rate produced void-free SiC films but the crystallinity of the films varied from single crystalline to polycrystalline. The growth of void-free single crystalline SiC films was observed at substrate temperatures below 1000°C. The outdiffusion of Si atoms from the Si substrate surface and the void formation in the silicon side of the SiC/Si interface were investigated using various experimental techniques. The mechanism of the void formation is briefly discussed in this work.

A model for the growth kinetics of a dielectric film obtained by oxidation of silicon in nitrous oxide environment is presented. The complete logarithmic form of oxidation kinetics is introduced for understanding the oxynitridation mechanism which includes information of the role of nitrogen in oxide film. The model fits experimental data excellently, both for short and long growth times. The chemical reaction energies of 1.81 and 1.1 eV are required for the oxynitridation for short and long growth times, respectively. This result suggests that the initial stage of the dielectric growth requires the higher reaction energy to form the SiO x N y layer and the lower energy is needed for the bulk oxide formation from the reaction with the interfacial layer of the SiO x N y . For the N 2 O oxidation, there are two barriers for the chemical reactions for NO and O 2 species dissociated from N 2 O molecules.

A theoretical description of the kinetic mechanism of thermal oxidation in silicon is proposed by complementing the Deal - Grove model. The relationship of the classical linear - parabolic growth law is generalized to the logarithmic growth law which provides a complete description for the whole regime of oxide films. In particular, the enhanced oxidation rate in the thin regime may be attributed to the diffusion length, which is characterized by the difference between the activation energies of the diffusion process and the reaction process. Our fitting of the logarithmic growth law to several experimental results shows excellent agreement and the fitting parameters also provide activation energies of 1.50 and 2.49 eV for the interfacial reaction and diffusion in oxide respectively.

The dependence of the forward operating voltage of In1−xGaxN/GaN light-emitting diodes (LEDs) on Mg flow rate during the growth of the p-GaN layer has been investigated. The hole concentration in the p-GaN layer increases with Mg flow rate up to a critical value and gradually decreases for higher flow rates. We find that the forward threshold voltage of the LEDs mainly depends on the Mg concentration in the p-GaN layer and is rather independent of hole concentration. A current flow mechanism involving the impurity acceptor band, instead of the usual valence band, is proposed to elucidate this anomalous behaviour of the I–V characteristics.