Structural Features and Properties of Bacterial Cellulose Produced in Agitated Culture

The structure and some properties of bacterial cellulose produced in agitated culture were studied. Scanning electron microscopy revealed that there was almost no difference between reticulated structures of bacterial cellulose fibrils produced in agitated culture and in static culture. Nevertheless, bacterial cellulose produced in agitated culture exhibited microstuctural changes, namely, a low degree of polymerization and a low crystallinity index. A CP/MAS ¹³C NMR analysis revealed that the cellulose I content of the cellulose produced in agitated culture was lower than that of the cellulose produced in static culture. The bacterial cellulose produced in agitated culture had a lower Young's modulus of sheet, a higher water holding capacity and a higher suspension viscosity in the disintegrated form than that produced in static culture.     

An on-membrane quantitative analysis system for glycyrrhizin in licorice roots and traditional Chinese medicines

An on-membrane quantitative analysis system has been developed for determining glycyrrhizin (GC) in licorice roots and traditional Chinese medicines. A GC standard and the extracts of licorice roots and traditional Chinese medicines were applied to a polyethersulfone (PES) membrane and were developed by acetonitrile/water/formic acid (45:55:2, by volume), then treated with a NaIO₄ solution followed by bovine serum albumin (BSA), resulting in a GC-BSA conjugate on a PES membrane. Anti-GC monoclonal antibody was bound and then a second antibody labeled with peroxidase directed against the first antibody. Finally a substrate reacted with the enzyme and gave staining. The stained membrane was scanned and coloring spots were analyzed quantitatively using graphic analysis by NIH Image software, indicating at least 0.5 μg of GC was clearly detectable. GC can be analyzed quantitatively between 1.0 and 8.0 μg.     

Molecular weight distribution and stereoregularity of polypropylenes produced with VCl4–AlEt2Cl catalyst

Dependences of the molecular weight distribution and stereochemical regulation of the polypropylenes produced with VCl₄–AlEt₂Cl catalyst on the polymerization temperature were examined. The molecular weight distributions of the polymers obtained at temperatures below ?40°C were unimodal and narrow (M _w/M _n ≤ 2). The molecular weight distributions obtained at higher temperatures (above ?21°C) were bimodal with one narrow distribution and one wide one (M _w/M _n > 2), and the polymer fraction of the wide distribution increased with the polymerization temperature. The fractional amount of ? (CH₂)₂? groups in the polymers, which corresponds to tail-to-tail linkage of two propylene units, increased to a maximum at ?21°C followed by a gradual decrease with the polymerization temperature. The production of isotactic polymers was confirmed at temperatures above ?21°C. From these data, it is concluded that only the homogeneous form of the catalyst system is responsible for the polymerization at temperatures below about ?21°C while the heterogeneous form appears and catalyzes the polymerization together with the homogeneous one at temperatures above ?21°C.     

Electrospun Cu-Deposited Flexible Fibers as an Efficient Oxygen Evolution Reaction Electrocatalyst

Developing oxygen evolution reaction (OER) catalysts with high activity, long-term durability, and at low cost remains a great challenge. Herein, we report the high activity of fibrous Cu-based catalysts. The synthesis process is simple and scalable. Electrospinning method was selected to synthesize fibrous polymer substrates (Poly(vinylidene fluoride-co-hexafluoropropylene, PVdF-HFP), which are then covered by Cu via electroless deposition. Cu-deposited PVdF-HFP with different microstructures having smooth and roughened surfaces were also synthesized by drop-casting and impregnation method, respectively, to emphasize the importance of the microstructures on OER activity. The OER activity and durability were studied by linear sweep voltammetry, chronoamperometry, and Tafel slope analysis. The Cu/PVdF-HFP fibrous catalysts exhibit significantly improved OER activity and durability compared with Cu plate as well as Cu-deposited PVdF-HFP with different microstructures. The unique fibrous structure provides better mass transport, diffusion, and large active surface area. In addition to the advantages of the fibrous structure, attenuated total reflection infrared (ATR-IR) and ex situ X-ray photoelectron spectroscopy revealed that the improved specific activity for Cu/PVdF-HFP fiber can be attributed to the synergistic effect between Cu and Cu/PVdF-HFP (electron transfer from Cu to PVdF-HFP) at the Cu|PVdF-HFP interface, which results in optimized reaction energetics for the OER.     

Synthesis of multi-functional epoxides derived from limonene oxide and its application to the network polymers

Bio-based multi-functional epoxides (1) such as bis-, tri-, and tetra-epoxides were synthesized by ene-thiol reactions between limonene oxide and polyhydric thiols. A cross-linking reaction of 1 with branched polyethyleneimine (BPEI) afforded the corresponding network polymers 2 with relatively high thermal resistance in high yields.     

Some thoughts on composition operators on subspaces of the Hardy space

Archiv der Mathematik - We discuss composition operators on certain subspaces of the Hardy space. The family of subspaces that we deal with are called $$H^2_{alpha , beta }$$ which have garnered...     

Density, viscosity and surface tension of 50RO-50P2O5 (R: Mg, Ca, Sr, Ba, and Zn) glass melts

The density, surface tension and viscosity of the 50RO-50P₂O₅ (R: Mg, Ca, Sr, Ba and Zn) glass melts have been measured over the range, 1073-1623 K. The effects of R cations on these properties have been investigated. The density of the melt was found to increase in the order, R: Mg<Ca<Zn<Sr<Ba, with increasing molar weight of cation. The surface tension in the temperature range of 1373-1473 K increased approximately with cation in the order, R: Zn<Ba<Mg<Ca<Sr. The viscosity and the negative, temperature coefficient of surface tension increased in the order, R: Ba<Sr<Ca<Zn<Mg. All melts exhibited negative temperature coefficients of surface tension. The effect of Mg and Zn cations on the properties were different to that for Ba, Sr, and Ca cations and this is discussed using bulk glass data published in a previous report. The features of Mg and Zn metaphosphate glass melts, that is high values of viscosity, and temperature coefficient of surface tension, are related to the small Oxygen Coordination Number of the cations (=4) when compared with those of Ca, Sr, Ba metaphosphate glass melts.     

On the dynamic model and motion planning for a spherical rolling robot actuated by orthogonal internal rotors

The paper deals with the dynamics of a spherical rolling robot actuated by internal rotors that are placed on orthogonal axes. The driving principle for such a robot exploits nonholonomic constraints to propel the rolling carrier. A full mathematical model as well as its reduced version are derived, and the inverse dynamics are addressed. It is shown that if the rotors are mounted on three orthogonal axes, any feasible kinematic trajectory of the rolling robot is dynamically realizable. For the case of only two rotors the conditions of controllability and dynamic realizability are established. It is shown that in moving the robot by tracing straight lines and circles in the contact plane the dynamically realizable trajectories are not represented by the circles on the sphere, which is a feature of the kinematic model of pure rolling. The implication of this fact to motion planning is explored under a case study. It is shown there that in maneuvering the robot by tracing circles on the sphere the dynamically realizable trajectories are essentially different from those resulted from kinematic models. The dynamic motion planning problem is then formulated in the optimal control settings, and properties of the optimal trajectories are illustrated under simulation.     

Synthesis of an amphiphilic polymer having hydrophobic acetal and hydrophilic pyrrolidone moieties and its application to persisting release of aldehyde as a pro‐fragrance

A polymer having acetal moiety in the side chain was synthesized by a reaction of 1,3‐diol structure of poly(vinyl alcohol‐co‐N‐vinylpyrrolidone) and octanal. The hydrophobicity of the resulting acetal moiety and the hydrophilicity of the pyrrolidone moiety allowed the polymer to exhibit amphiphilicity. The polymer released octanal by hydrolysis of the acetal side chains under acidic conditions. The release of octanal was enhanced by the increased hydrophilicity of the polymer because of the presence of pyrrolidone moiety. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3816–3822, 2010