Multiscale characterization of antimicrobial poly(vinyl butyral)/titania nanofibrous composites

Titania nanofillers were used to reinforce nanofibers in composite mats produced by electrospinning of poly(vinyl butyral) with two different concentrations of polymers. The titania nanoparticles and titania nanotubes were added into an acetic acid/ethanol solution in different contents of 3 and 1 wt%, respectively. The effect of the processing system on the morphology of the produced fibers was analyzed. The antimicrobial poly(vinyl butyral) composite fibers with titanium dioxide nanoparticles and titanium dioxide nanotubes were produced by single and multineedle electrospinning systems. This study reports fabrication of composite nanofibrous mats with significant mechanical and antimicrobial properties at a high production speed, which is promising for commercial applications (health care, photocatalysis, protective clothing, etc.). The reported result revealed an outstanding correlation between values of elastic modulus derived from nanoindentation and dynamic mechanical techniques. Copyright © 2017 John Wiley & Sons, Ltd.     

Rates of convergence in certain limit theorem for extreme values

Let be independent random variables with the common negative binomial distribution with parameters r>0 and 1/n, where r is not necessarily an integer. We determine the limiting distribution of the random variable as n→∞, corresponding normalizing constants and the rate of convergence. For an integer r the connection with certain waiting time problems is indicated.     

Theoretical Considerations about Near-Wall Turbulence and Resulting Flow Control Schemes

Based on analytical considerations about how near-wall turbulence needs to be modified in order to reduce the momentum loss towards solid walls and to yield lower energy losses, a mechanism of turbulent drag reduction is proposed. This mechanism suggests that drag reducing flow control at high Reynolds numbers should be designed to minimize the turbulent dissipation rate. A previously published approach on how a reduction of the turbulent dissipation in the near-wall region can be achieved is analyzed further. The obtained results provide some new insight on the parameters that need to be considered when designing flow control schemes for skin friction drag reduction. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impedance spectroscopy of reactive polymers. 1

Dielectric measurements were utilized to follow the advancement of cure in an epoxy/amine formulation. In contrast to earlier studies, complex impedance was measured during cure and used to calculate ionic resistivity. By using complex impedance were able to separate according to their frequency dependence the contributions to overall polarization from electrode blocking layers, migrating charges, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial-and-error frequency search and is conducive to the development of phenomenological models based on equivalent circuits. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. © 1994 John Wiley & Sons, Inc.     

Study of molecular deformation mechanisms in the glassy state. I. Temperature effect on stress-birefringence and strain-birefringence responses of poly(methyl methacrylate)

In order to gain better understanding of the molecular deformation processes occurring in poly-(methyl methacrylate), a series of studies was carried out in uniaxial tension on the simultaneous stress and birefringence response in both constant-strain-rate and stress relaxation experiments. The former covered the temperature range ?120 to 75°C and the latter 0 to 90°C. Three deformation mechanisms, i.e., (i) change in intermolecular distance, (ii) distortion of the conformation of the COOCH₃ group from its thermal equilibrium state, and (iii) orientation of main-chain segments, are invoked to interpret the experimental results. It is concluded that, in the temperature range from ?120 to 75°C and possibly at higher temperatures as well, the polymer chains deform in the small-strain region by an orientation of those chain segments having lower potential-energy barriers to conformational changes and straining those chain segments having higher potential-energy barriers. Subsequent chain orientation of the already strained segments occur in the higher strain regions. Changes in intermolecular distances occur over the entire temperature range from ?120 to 90°C, but their magnitude decreases gradually as the temperature increases from ?40 to 40°C and then decreases sharply for temperatures above 40°C. Strain-induced distortion of the conformation of the COOCH₃ group may involve only rotation of the OCH₃ group around the C? O bond rather than rotation of the entire ester group itself.     

Thermodynamic and kinetic properties of phonons in cylindrical quantum dots

The Green's function technique, suitable for analyses of spatially deformed structures, is developed in this paper and applied to phonon system. The thermodynamic and kinetic phonon properties of cylindrical quantum dots are analysed using a developed method. As a consequence of the applied new method the configurational dependence of diffusion coefficient and dot's density were included into calculations. Maximum of diffusion and minimum of density is located in central part of the cylindrical quantum dot. All thermodynamic and kinetic characteristics of quantum dot are exponentially small at low temperatures. The low phonons specific heat as well as the low thermal conductivity lead to conclusion that in cylindrical quantum dots exist more convenient conditions for appearance of electron superconductivity.     

The Reduction of Some 1, 2-Epoxides with Lithium Aluminium Hydride. Preliminary Communication

The factors influencing the ease of the lithium aluminium hydride reduction of various 1,2-epoxycycloalkanes and 1,2-epoxyalkanes are described and discussed.     

Excited singlet states of covalently bound, cofacial dimers and trimers of perylene-3,4:9,10-bis(dicarboximide)s

Perylene-3,4:9,10-bis(dicarboximide) (PDI) and its derivatives are robust organic dyes that strongly absorb visible light and display a strong tendency to self-assemble into ordered aggregates, having significant interest as photoactive materials in a wide variety of organic electronics. To better understand the nature of the electronics states produced by photoexcitation of such aggregates, the photophysics of a series of covalent, cofacially oriented, pi-stacked dimers and trimers of PDI and 1,7-bis(3',5'-di-t-butylphenoxy)perylene-3,4:9,10-bis(dicarboximide) (PPDI) were characterized using both time-resolved absorption and fluorescence spectroscopy. The covalent linkage between the chromophores was accomplished using 9,9-dimethylxanthene spacers. Placing n-octyl groups on the imide nitrogen atoms at the end of the PDI chromophores not attached to the xanthene spacer results in PDI dimers having near optimal pi-stacking, leading to formation of a low-energy excimer-like state, while substituting the more sterically demanding 12-tricosanyl group on the imides causes deviations from the optimum that result in slower formation of an excimer-like excited state having somewhat higher energy. By comparison, PPDI dimers having terminal n-octyl imide groups have two isomers, whose photophysical properties depend on the ability of the phenoxy groups at the 1,7-positions to modify the pi stacking of the PPDI molecules. In general, disruption of optimal pi-stacking by steric interactions of the phenoxy side groups results in excimer-like states that are higher in energy. The corresponding lowest excited singlet states of the PDI and PPDI trimers are dimer-like in nature and suggest that structural distortions that accompany formation of the trimers are sufficient to confine the electronic interaction on two chromophores within these systems. This further suggests that it may be useful to build into oligomeric PDI and PPDI systems some degree of flexibility that allows the structural relaxations necessary to promote electronic interactions between multiple chromophores.     

Structural and Vibrational Characterization of the Chromophore Binding Site of Bacterial Phytochrome Agp1

Agp1 is a prototypical bacterial phytochrome from Agrobacterium fabrum harboring a biliverdin cofactor which reversibly photoconverts between a red‐light‐absorbing (Pr) and a far‐red‐light‐absorbing (Pfr) states. The reaction mechanism involves the isomerization of the bilin‐chromophore followed by large structural changes of the protein matrix that are coupled to protonation dynamics at the chromophore binding site. Histidines His250 and His280 participate in this process. Although the three‐dimensional structure of Agp1 has been solved at high resolution, the precise position of hydrogen atoms and protonation pattern in the chromophore binding pocket has not been investigated yet. Here, we present protonated structure models of Agp1 in the Pr state involving appropriately placed hydrogen atoms that were generated by hybrid quantum mechanics/molecular mechanics‐ and electrostatic calculations and validated against experimental structural‐ and spectroscopic data. Although the effect of histidine protonation on the vibrational spectra is weak, our results favor charge neutral H250 and H280 both protonated at Nε. However, a neutral H250 with a proton at Nε and a cationic H280 may also be possible. Furthermore, the present QM/MM calculations of IR and Raman spectra of Agp1 containing isotope‐labeled BV provide a detailed vibrational assignment of the biliverdin modes in the fingerprint region.     

Plasma electrochemistry: electroreduction in a flame

The manipulation of electron transfer reactions at surfaces forms the cornerstone of electrodeposition and processing of materials on substrates with precise control of stoichiometry and oxidation state. However, the utility of this technique, which is mainly carried out in liquid electrolytes, is ultimately limited by the electrolysis of the solvent which limits a potential window to at best 4.8 V in nonaqueous solutions (A. J. Bard and L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, Wiley, New York, NY, 2nd edn, 2001; ref. 1) and can be up to 6 V in ionic liquids (A. P. Abbott, K. J. McKenzie, Phys. Chem. Chem. Phys., 2006, 8, 4265-4279; ref. 2). A long-sought-after goal has been to develop a corresponding technique at the solid/gas interface in the absence of a solvent which will allow in principle a potential window in excess of 100 V (J. M. Goodings, J. Guo, A. N. Hayhurst and S. G. Taylor, Int. J. Mass Spectrom., 2001, 206, 137-151; ref. 3). This extended potential window will enable chemistry at the solid/gas interface that is not possible at the solid/liquid interface. Here we describe a new approach to gas-phase electrochemistry using a flame plasma as the electrolyte medium. We demonstrate the controlled electrochemical reduction of Cu(+) to Cu(0) at an electrode surface in a flame environment with resulting deposition of either Cu(2)O or Cu species on conducting diamond electrodes. This approach is novel in that it involves the application of an electrochemical potential difference to change the redox state of surface confined species, not the measurement of flame bore ions (as in flame ionisation detectors). This new technique will permit deposition of films and particles on surfaces with control over the oxidation state of the species. This will provide a valuable enhancement to the capabilities of materials preparation methods such as flame spray deposition.