Molecular origin of unusual physical and mechanical properties in novel phenolic materials based on benzoxazine chemistry

The effect of temperature on hydrogen bonding was investigated by measuring the integrated infrared absorbance of various hydrogen-bonding modes as a function of temperature. It was found that conformationally preferred hydrogen- bonding modes maintain constant intensities over the wide temperature ranges studied for both polybenzoxazines and a novolac-type phenolic resin. In particular, the O— — —H— — —N hydrogen bond shows strong bonding that does not change over the temperature range. On the other hand, statistically distributed hydrogen bonding is more sensitive to the temperature change and its infrared intensities start decreasing around the β-transition of polybenzoxazines. The unusual physical and mechanical properties of polybenzoxazines, including volumetric expansion upon polymerization, high moduli, and high glass transition temperatures, are explained based on the complex hydrogen bonding. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1299–1306, 1998     

Facile preparation of polybenzoxazine-based carbon microspheres with nitrogen functionalities: effects of mixed solvents on pore structure and supercapacitive performance

In this study, polybenzoxazine (PBZ)-based carbon microspheres were prepared via a facile method using a mixture of formaldehyde (F) and dimethylformamide (DMF) as the solvent. The PBZ microspheres were successfully obtained at the F/DMF weight ratios of 0.4 and 0.6. These microspheres exhibited high nitrogen contents after carbonization. The microstructures of all the samples showed an amorphous phase and a partial graphitic phase. The porous carbon with the F/DMF ratio of 0.4 showed significantly higher specific capacitance (275.1 F∙g^‒1) than the reference carbon (198.9 F∙g^‒1) at 0.05 A∙g^‒1. This can be attributed to the synergistic electrical double-layer capacitor and pseudo-capacitor behaviors of the porous carbon with the F/DMF ratio of 0.4. The presence of nitrogen/oxygen functionalities induced pseudo-capacitance in the microspheres, and hence increased their total specific capacitance. After activation with CO₂, the specific surface area of the carbon microspheres with the F/DMF ratio of 0.4 increased from 349 to 859 m²∙g^‒1 and the specific capacitance increased to 424.7 F∙g^‒1. This value is approximately two times higher than that of the reference carbon. The results indicated that the F/DMF ratio of 0.4 was suitable for preparing carbon microspheres with good supercapacitive performance. The nitrogen/oxygen functionalities and high specific surface area of the microspheres were responsible for their high capacitance.     

Enhancement of the Skin Permeation of Clindamycin Phosphate by Aerosol OT/1-Butanol Microemulsions

Microemulsions of water/isopropyl palmitate (IPP)/Aerosol OT (AOT)/1-butanol were developed as alternative formulations for topical delivery of clindamycin phosphate. Effect of AOT:1-butanol ratios on microemulsion region existence in the pseudoternary phase diagrams was investigated. The 2:1 AOT:1-butanol provided the largest microemulsion region. Five microemulsions of 1% w/w clindamycin phosphate were prepared and characterized. The permeation through human epidermis of the microemulsions was evaluated and compared with the 70% isopropanol solution using modified Franz diffusion cells. The drug permeation from all microemulsions was found to be significantly greater than that from the solution, indicating the enhancement of the skin permeation by the microemulsions. Within the same microemulsion type, the drug permeation increased with increasing the amount of AOT:1-butanol. The drug permeation from oil-in-water (o/w) microemulsions was relatively higher than that from water-in-oil (w/o) microemulsions. In addition, all microemulsions were stable for at least three months at 30 ± 1°C.     

Structural Aspects of SBA-1 Cubic Mesoporous Silica Synthesized via a Sol–Gel Process Using a Silatrane Precursor

Silatrane prepared from fumed silica and triethanolamine was used as a precursor for SBA-1 synthesis at room temperature using cationic surfactants, derived from alkyltrimethylammonium bromides, C _n TMAB ( n =14, 16, and 18), as templates in dilute solutions. The influence of acidity, alkyl chain length of the surfactant, and synthesis temperature was studied. The shape of the SBA-1 crystals was dependent on the alkyl chain length of the surfactant. At a high surfactant concentration and an elevated reaction temperature (50°C), three-dimensionally ordered mesopores were invariably produced. Both X-ray diffraction and transmission electron microscopic results showed characteristics of the three-dimensional cubic structure. Scanning electron microscopic images of SBA-1 indicated the crystalline-like appearance of an octadecahedron (18-hedron) consistent with six square {100} and 12 hexagonal {110} planes with a cubic symmetry. The surface area of the product was as high as 1000–1500 m²/g with an adsorption volume of 0.6–1.0 cm³/g.     

Preparation of zirconia powders by sol-gel route of sodium glycozirconate complex

Zirconia powders were prepared by a sol-gel method, using sodium glycozirconate complex as precursor synthesized via the Oxide One Pot Synthesis (OOPS) process. Gelation of this precursor was achieved through the variation of the hydrolysis ratio without the use of the dopants. The gel samples were also calcined at different temperatures. The resulting zirconia was characterized using X-ray diffraction (XRD), SEM and nitrogen adsorption/desorption. The solid materials obtained after heat treatment at 500 °C by varying the hydrolysis ratio have large surface areas of 154-220 m² g⁻¹ and a narrow pore size distribution in the mesopore region. By variation of the heat treatment, the zirconia xerogels existed in either an amorphous, tetragonal, or monoclinic form at room temperature. Based on XRD data the first identifiable crystalline structure developed from the amorphous phase was the tetragonal polymorph, which was formed between 500 and 800 °C. When the temperature was raised to 1000 °C, zirconia powder with a monoclinic structure was obtained. Surface areas about 280 m² g⁻¹ was obtained after calcination at 400 °C, which drop to ca. 70 m² g⁻¹ following treatment at 1000 °C.     

Highly dispersed Mo-MCM-41 produced from silatrane and molybdenum glycolate precursors and its peroxidation activity

High surface area and high dispersion Mo/MCM-41 catalysts were successfully prepared using high-purity silatrane and molybdenum glycolate precursors. The precursors were synthesized using the Oxide One Pot Synthesis (OOPS) process. Mo was loaded onto MCM-41 by impregnation before and after heat treatment. After heat treatment, the catalysts were characterized using DRUV, XRD, FTIR, Laser Raman and BET. The %Mo dispersion was as high as 10 mol% or 0.265 g MoO₃/g SiO₂ while the structure of MCM-41 was still retained. Bulk MoO₃ was observed in the case of Mo-loaded onto the calcined support of MCM-41(c). The Mo-loaded uncalcined silicate MCM-41 support showed better catalytic activity during the peroxidative reaction.     

Electrorheological properties of novel piezoelectric lead zirconate titanate Pb(Zr0.5,Ti0.5)O3-acrylic rubber composites

Perovskite lead zirconate titanate, comprised of PbTi_1 ? xO₃ and PbZr_xO₃, was synthesized at a temperature below the Curie temperature, T_C. The tetragonal form obtained is a noncentrosymmetric structure capable of spontaneous polarization. FTIR spectra and XRD patterns confirm the successful synthesis of the lead zirconate titanate (PZT). PZT particles were mixed with an arcrylic rubber solution and cast as a thin sheet. SEM micrographs indicate that PZT particles are moderately dispersed in the acrylic rubber (AR71) matrix. Without electric field, the particles merely act as a reinforcing filler which can absorb and store additional stress. Under electric field, particle-induced dipole moments are generated, leading to interparticle interactions, and a substantial increase in the storage modulus. At a lead zirconate titanate volume fraction of 0.038600, the storage modulus response attains its maximum value with the corresponding storage modulus sensitivity value of 0.58 as the electric field strength is varied from 0 to 2 kV/mm.     

Local Structure Investigation in Multiferroic BiFeO3–BaTiO3 Ceramics by XAS Technique and Their Relevant Properties

The (1?x)BiFeO₃‐xBaTiO₃ (with x = 0.1, 0.2, 0.3, and 0.4) ceramics were fabricated successfully by solid‐state reaction method. Single‐phase perovskite was obtained in all ceramics, as confirmed by XRD technique. It was observed that 0.7BiFeO₃–0.3BaTiO₃ was the morphotropic phase boundary (MPB) between rhombohedral and cubic phases, as also revealed from ferroelectric and magnetic properties. The simulated and experimental X‐Ray Absorption Spectroscopy (XAS) study revealed that BT in 0.75BF‐0.25BT is possibly taken a rhombohedral structure. Furthermore, the rounded ferroelectric hysteresis loops observed for 0.9BiFeO₃–0.1BaTiO₃ and 0.8BiFeO₃–0.2BaTiO₃ compositions could be attributed to their microstructure and surface charge effects and electron transfer between Fe³⁺ and Fe²⁺ ions. It was also found that high dielectric constant of 0.9BiFeO₃–0.1BaTiO₃ composition was a result of grain and grain‐boundary effects, as observed in SEM micrographs. In addition, a strong signature of dielectric relaxation behavior was observed in this ceramic system with the activation energy 0.467 eV obtained from the Arrhenius' law. Finally, the local structure investigation with XAS technique provided additional information to better understand the electric and magnetic properties in the BF‐BT ceramic system.