Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies.     

Molecular simulation study of dynamical properties of room temperature ionic liquids with carbon pieces

Room temperature ionic liquids (RTILs) with dispersed carbon pieces exhibit distinctive physiochemical properties. To explore the molecular mechanism, RTILs/carbon pieces mixture was investigated by molecular dynamics (MD) simulation in this work. Rigid and flexible carbon pieces in the form of graphene with different thicknesses and carbon nanotubes in different sizes were dispersed in a representative RTIL 1-butyl-3-methyl-imidazolium dicyanamide ([Bmim][DCA]). This study demonstrated that the diffusion coefficients of RTILs in the presence of flexible carbons are similar to those of bulk RTILs at varying temperatures, which is in contrast to the decreased diffusion of RTILs in the presence of rigid carbons. In addition, interfacial ion number density at rigid carbon surfaces was higher than that at flexible ones, which is correlated with the accessible external surface area of carbon pieces. The life time of cation-anion pair in the presence of carbon pieces also exhibited a dependence on carbon flexibility. RTILs with dispersed rigid carbon pieces showed longer ion pair life time than those with flexible ones, in consistence with the observation in diffusion coefficients. This work highlights the necessity of including the carbon flexibility when performing MD simulation of RTILs in the presence of dispersed carbon pieces in order to obtain the reliable dynamical and interfacial structural properties.     

Laser-induced thermal-acoustic velocimetry with heterodyne detection

Laser-induced thermal acoustics (LITA) was used with heterodyne detection to measure simultaneously and in a single laser pulse the sound speed and flow velocity of NO>(2) -seeded air in a low-speed wind tunnel up to Mach number M =0.1 . The uncertainties of the velocity and the sound speed measurements were ~0.2 m/s and 0.5%, respectively. Measurements were obtained through a nonlinear least-squares fit to a general, analytic closed-form solution for heterodyne-detected LITA signals from thermal gratings. Agreement between theory and experiment is exceptionally good.     

Performance impact of dynamic surface coatings on polymeric insulator-based dielectrophoretic particle separators

Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulator-based dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant coatings provide an affordable engineering strategy for selective particle enrichment and sorting. Figure Model generated image (COMSOL) depicting the electric field gradient divided by the electric field that occurs within an array of insulating posts     

Collisional deactivation of Ba 5d7p (3)D1 by noble gases

Collisional deactivation of the 5d7p (3)D1 state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency-doubled dye laser at 273.9 nm excites the 5d7p (3)D1 level from the ground state, and fluorescence at 364.1 and 366.6 nm from the 5d7p (3)D1 --> 6s5d (3)D1 and 5d7p (3)D1 --> 6s5d (3)D2 transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) s(-1); Ar, (4.53 +/- 0.15) x 10(-10) cm(3) s(-1); Kr, (4.64 +/- 0.13) x 10(-10) cm(3) s(-1); Xe, (5.59 +/- 0.22) x 10(-10) cm(3) s(-1). From time-resolved 5d7p (3)D1 emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d (3)D3, 28 +/- 3 ns; 5d7p (3)P1, 46 +/- 2 ns; 5d6d (3)G3, 21.5 +/- 0.8 ns; 5d7p (3)F3, 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p (3)D1 state to eleven near-resonant fine structure states.     

Phase coexistence in polydisperse athermal polymer-colloidal mixture

A theoretical scheme developed earlier [Y. V. Kalyuzhnyi et al., Chem. Phys. Lett. 443, 243 (2007)] is used to calculate the full phase diagram of polydisperse athermal polymer-colloidal mixture with polydispersity in both colloidal and polymeric components. In the limiting case of bidisperse polymer-colloidal mixture, theoretical results are compared against computer simulation results. We present the cloud and shadow curves, critical binodals, and distribution functions of the coexisting phases and discuss the effects of polydispersity on their behavior. According to our analysis polydispersity extends the region of the phase instability, shifting the critical point to the lower values of the pressure and density. For the high values of the pressure polydispersity causes strong fractionation effects, with the large size colloidal particles preferring the low-density shadow phase and long chain length polymeric particles preferring the high-density shadow phase.     

Measurement of the eta'-meson mass using J/psi-->gammaeta'

We measure the mass of the eta;{'} meson using psi(2S)-->pi;{+}pi;{-}J/psi, J/psi-->gammaeta;{'} events acquired with the CLEO-c detector operating at the CESR e;{+}e;{-} collider. Using three decay modes, eta;{'}-->rho;{0}gamma, eta;{'}-->pi;{+}pi;{-}eta with eta-->gammagamma, and eta;{'}-->pi;{+}pi;{-}eta with eta-->pi;{+}pi;{-}pi;{0}, we find M_{eta;{'}}=957.793+/-0.054+/-0.036 MeV, in which the uncertainties are statistical and systematic, respectively. This result is consistent with but substantially more precise than the current world average.     

The attenuation of lined plenum chambers in ducts,II: Measurements and comparison with theory

Experimental measurements of the acoustic performance of single and three-pass lined plenum chambers are compared to calculations based on theoretical models described in a companion paper [1]. Generally, quite good agreement is obtained, subject to the limitations of the theories. For the sake of completeness, comparison is made between the performance of a single plenum chamber and that of an equivalent splitter silencer. The two are seen to differ somewhat in their attenuation characteristics. The aerodynamic pressure losses of all three silencers are compared, and observations are made concerning the relative mass, construction time, et cetera, of the single chamber and the splitter. A tentative design procedure for plena is suggested.     

Synthesis of α-SnWO4 thin-film electrodes by hydrothermal conversion from crystalline WO3

Thin film electrodes of the orthorhombic form of tin tungstate (α-SnWO4) were prepared using a hydrothermal method to convert thin films of WO3 in aqueous SnCl2. The pH dependence of the growth mechanism was identified by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD patterns show complete conversion of WO3(s) to SnWO4(s) at pH 1, 4, and 7. SEM images reveal a morphology change from sponge-like platelets to sharp nanowires as the pH increases from 1 to 7. The α-SnWO4 thin films were reddish brown in color, and display an indirect band gap of 1.9 eV by diffuse reflectance UV-vis spectroscopy. α-SnWO4 is therefore solar-responsive, and a chopped light linear sweep voltammogram recorded under 100 mW/cm2 AM1.5 simulated solar illumination in a pH 5 0.1 mol/L KPi buffer show a visible light response for photoelectrochemical water oxidation, producing 32 mA/cm2 at 1.23 V vs. RHE.