Self assembled composites of luminescent Ru(II) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4-

The interaction of two luminescent metallopolymers; [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP)co-poly(7)](+), where bpy is 2,2'-bipyridyl, PVP is polyvinylpyridine, and (CAIP)co-poly(7) is poly(styrene(6)-co-p-(aminomethyl)styrene) amide linked to 2-(4-carboxyphenyl)imidazo[4,5-f] [1,10]phenanthroline, with the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-) is described. Both metallopolymers undergo electrostatic association with the polyoxometalate. From both electronic and luminescence spectroscopy the thermodynamic products were determined to be {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) and {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+), i.e. in both instances, the number of ruthenium centres in the cluster exceeds the number required for charge neutralization of the molybdate centre. Association quenches the luminescence of the metallopolymer although, consistent with the excess of Ru(ii) present in the associated composites, emission is not completely extinguished even when a large excess of [Mo(18)O(54)(SO(4))(2)](4-) is present. The observed emission lifetime was not affected by [Mo(18)O(54)(SO(4))(2)](4-) therefore quenching was deemed static. The luminescent intensity data was found to fit best to a (sphere of action) Perrin model from which the radii of the quenching were calculated as 4.6 ? and 5.8 ? for [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP co-poly)(7)](+) respectively. Both UV/Vis and resonance Raman data indicate the presence of a new optical transition centered around 490 nm for the composite, {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). This indicates strong electronic interaction between the metal centres in the former composite, which despite good thermodynamic analogy, is not observed for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). These results are consistent with photoelectrochemical studies of layer by layer assemblies of these films which indicate that the ruthenium centre sensitizes polyoxometalate photo-oxidation of benzyl alcohol in {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not in {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+).     

Adsorption of sterically stabilized latex particles at liquid surfaces: effects of steric stabilizer surface coverage, particle size, and chain length on particle wettability

A series of five near-monodisperse sterically stabilized polystyrene (PS) latexes were synthesized using three well-defined poly(glycerol monomethacrylate) (PGMA) macromonomers with mean degrees of polymerization (DP) of 30, 50, or 70. The surface coverage and grafting density of the PGMA chains on the particle surface were determined using XPS and (1)H NMR spectroscopy, respectively. The wettability of individual latex particles adsorbed at the air-water and n-dodecane-water interfaces was studied using both the gel trapping technique and the film calliper method. The particle equilibrium contact angle at both interfaces is relatively insensitive to the mean DP of the PGMA stabilizer chains. For a fixed stabilizer DP of 30, particle contact angles were only weakly dependent on the particle size. The results are consistent with a model of compact hydrated layers of PGMA stabilizer chains at the particle surface over a wide range of grafting densities. Our approach could be utilized for studying the adsorption behavior of a broader range of sterically stabilized inorganic and polymeric particles of practical importance.     

Formation of N719 dye multilayers on dye sensitized solar cell photoelectrode surfaces investigated by direct determination of element concentration depth profiles

The structure of the dye layer adsorbed on the titania substrate in a dye-sensitized solar cell is of fundamental importance for the function of the cell, since it strongly influences the injection of photoelectrons from the excited dye molecules into the titania substrate. The adsorption isotherms of the N719 ruthenium-based dye were determined both with a direct method using the depth profiling technique neutral impact collision ion scattering spectroscopy (NICISS) and with the standard indirect solution depletion method. It is found that the dye layer adsorbed on the titania surface is laterally inhomogeneous in thickness and there is a growth mechanism already from low coverage levels involving a combination of monolayers and multilayers. It is also found that the amount of N719 adsorbed on the substrate depends on the titania structure. The present results show that dye molecules in dye-sensitized solar cells are not necessarily, as presumed, adsorbed as a self-assembled monolayer on the substrate.     

Surface structure of In2O3(111) (1 × 1) determined by density functional theory calculations and low energy electron diffraction

The surface structure of In₂O₃(111) has been investigated by dynamical analysis of low energy electron diffraction data, in conjunction with first principles calculations using density functional theory. The experimental data set consisted of eight independent beams whose intensities were measured for incident energies in the range between 25 eV and 250 eV. In fitting the experimental data it was essential to treat the radii of In and O spheres as variable parameters: following this procedure a final Pendry R factor of 0.31 was obtained. The LEED results are compatible with the calculations and both analyses suggest that the surface structure involves only small vertical relaxations in the outermost of the {[O^2?]₁₂^24?[In³⁺]₁₆⁴⁸⁺[O^2?]₁₂^24?} quadrupolar units that define the (111) surface. The ab initio slab calculations also confirm that lateral relaxations not considered in fitting the experimental data are of very minor importance.     

Enhanced photocurrent production from thin films of Ru(II) metallopolymer/Dawson polyoxotungstate adducts under visible irradiation

Thin films of polyoxometalates that are sensitized with a Ru(II) metallopolymer generate significant photocurrents in the presence of benzyl alcohol and visible light. Significantly, the photocurrent generated by the tungstate based adduct, α-[P(2)W(18)O(62)](6-), is approximately seven fold larger than that found for the Dawson polyoxomolybdate α-[S(2)Mo(18)O(62)](4-).     

Pressure drop in two phase slug/bubble flows in mini scale capillaries

A segmented two phase slug/bubble flow occurs where a liquid and a gas are pumped into the same tube over a range of Reynolds numbers. This segmented two phase flow regime is accompanied by an increase in pressure drop relative to the single phase flow where only one fluid is flowing in a capillary. This work experimentally and theoretically examines the pressure drop encountered by the slug/bubble flow with varying slug lengths in mini channels. In the experimental work the dimensionless parameters of Reynolds number and Capillary number span over three orders of magnitude, and dimensionless slug length ranges over two orders of magnitude to represent flows typical of mini- and micro-scale systems. It is found, in agreement with previous work, that these dimensionless groups provide the correct scaling to represent the pressure drop in two phase slug/bubble flow, although the additional pressure drop caused by the interface regions was found to be ∼40% less than previously reported.     

Photolysis of (Me2Si)6 in argon matrices doped with high concentrations (ca. 20%) of N2O or C2H4O: formation of (Me2SiO)6

Irradiation using a low pressure mercury lamp (λ=ca. 250 nm) of argon matrices containing ca. 1% (Me₂Si)₆ and ca. 20% ethylene oxide (C₂H₄O) or nitrous oxide (N₂O) for a period of ca. 20 h leads to the formation of the cyclic compound (Me₂SiO)₆. This has a 12-membered ring with alternating Si and O atoms. It is identified by comparison of its infrared spectrum with a spectrum of an authentic sample. The reaction appears to proceed by stepwise insertion of O atoms into Si---Si bonds.     

Squeeze-film flow of an Oldroyd-B fluid: Similarity solution and limiting Weissenberg number

Summary In this paper we consider the motion of an Oldroyd-B fluid being squeezed between two parallel disks of infinite extent. We show that a similarity solution exists provided that the fluid inertia is neglected and that the squeezing velocity varies exponentially with time. We prove that there is a critical Weissenberg number above which at least one component of the stresses grows unboundedly with time. This critical Weissenberg number is of the order of 0.67. This latter conclusion is also valid in the continuous squeeze-film mode.

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Zusammenfassung In diesem Artikel betrachten wir die Bewegung einer Oldroyd-B Flüssigkeit welche zwischen zwei parallele Scheiben von unendlicher Dimension gequetscht wird. Es wird gezeigt, daß eine Similaritätslösung existiert, vorausgesetzt, daß die Flüssigkeitsträgheit vernachlässigt wird und die Quetschgeschwindigkeit sich exponentiell mit der Zeit verändert. Der Beweis wird erbracht, daß eine kritische Weissenbergzahl existiert, oberhalb welcher wenigstens eine Komponente der Spannungen mit der Zeit anwächst. Diese kritische Weissenbergzahl ist in der Größenordnung von 0.67. Dasselbe Resultat gilt für den kontinuierlichen Quetsch-Film.