Synthesis and properties of oxetane‐based polysiloxanes used for cationic UV curing coatings

The polysiloxanes end‐capped with oxetane group (PSiO‐H and PSiO‐L) were synthesized via hydrosilylation reaction based on α,ω‐dihydrogen‐terminated polydimethylsiloxanes with a higher (0.23%, PDSi‐H) and lower (0.12%, PDSi‐L) hydrogen amount. The molecular structures were characterized by FT‐IR and ¹H NMR spectroscopy. The polysiloxanes were added into a commercial oxetane‐based resin, 3,3′‐(oxydi(methylene)) bis(3‐ethyloxetane) (DOX), as an additive to prepare a series of cationic UV curable formulations. The photo‐DSC results showed that the maximum photopolymerization rate decreased while the oxetane conversion increased with the polysiloxane content increasing. The surface hydrophobic property of cured films was improved having the water contact angles of 97° and 99° compared with 82° of the cured DOX film with only 1 wt% PSiOs, respectively. The dynamic mechanical thermal analysis results showed that both the storage modulus on the rubbery plateau region and the glass transition temperature decreased with increasing PSiO‐H loading. Moreover, the decrease became more obvious as PSiO‐L was added instead of PSiO‐H due to its lower concentration of oxetane group. The thermal stability of cured films was enhanced by the addition of PSiOs from the thermogravimetric analysis. And the DOX/PSiO‐H film possessed higher thermal degradation temperatures than DOX/PSiO‐L film. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative Analysis of Polymer Additives with MALDI-TOF MS Using an Internal Standard Approach

MALDI-TOF MS is used for the qualitative analysis of seven different polymer additives directly from the polymer without tedious sample pretreatment. Additionally, by using a solid sample preparation technique, which avoids the concentration gradient problems known to occur with dried droplets and by adding tetraphenylporphyrine as an internal standard to the matrix, it is possible to perform quantitative analysis of additives directly from the polymer sample. Calibration curves for Tinuvin 770, Tinuvin 622, Irganox 1024, Irganox 1010, Irgafos 168, and Chimassorb 944 are presented, showing coefficients of determination between 0.911 and 0.990.     

Decaborane thiols as building blocks for self-assembled monolayers on metal surfaces

Three nido-decaborane thiol cluster compounds, [1-(HS)-nido-B(10)H(13)] 1, [2-(HS)-nido-B(10)H(13)] 2, and [1,2-(HS)(2)-nido-B(10)H(12)] 3 have been characterized using NMR spectroscopy, single-crystal X-ray diffraction analysis, and quantum-chemical calculations. In the solid state, 1, 2, and 3 feature weak intermolecular hydrogen bonding between the sulfur atom and the relatively positive bridging hydrogen atoms on the open face of an adjacent cluster. Density functional theory (DFT) calculations show that the value of the interaction energy is approximately proportional to the number of hydrogen atoms involved in the interaction and that these values are consistent with a related bridging-hydrogen atom interaction calculated for a B(18)H(22)·C(6)H(6) solvate. Self-assembled monolayers (SAMs) of 1, 2, and 3 on gold and silver surfaces have been prepared and characterized using X-ray photoelectron spectroscopy. The variations in the measured sulfur binding energies, as thiolates on the surface, correlate with the (CC2) calculated atomic charge for the relevant boron vertices and for the associated sulfur substituents for the parent B(10)H(13)(SH) compounds. The calculated charges also correlate with the measured and DFT-calculated thiol (1)H chemical shifts. Wetting-angle measurements indicate that the hydrophilic open face of the cluster is directed upward from the substrate surface, allowing the bridging hydrogen atoms to exhibit a similar reactivity to that of the bulk compound. Thus, [PtMe(2)(PMe(2)Ph)(2)] reacts with the exposed and acidic B-H-B bridging hydrogen atoms of a SAM of 1 on a gold substrate, affording the addition of the metal moiety to the cluster. The XPS-derived stoichiometry is very similar to that for a SAM produced directly from the adsorption of [1-(HS)-7,7-(PMe(2)Ph)(2)-nido-7-PtB(10)H(11)] 4. The use of reactive boron hydride SAMs as templates on which further chemistry may be carried out is unprecedented, and the principle may be extended to other binary boron hydride clusters.     

Coumarin 314 free radical cation: formation, properties, and reactivity toward phenolic antioxidants

We have explored the photogeneration of the coumarin 314 radical cation by using nanosecond laser excitation at wavelengths longer than 400 nm in benzene, acetonitrile, dichloromethane, and aqueous media. In addition, time-resolved absorption spectroscopy measurements allowed detection of the triplet excited state of coumarin 314 (C(314)) with a maximum absorption at 550 nm in benzene. The triplet excited state has a lifetime of 90 μs in benzene. It is readily quenched by oxygen (k(q) = 5.0 × 10(9) M(-1) s(-1)). From triplet-triplet energy transfer quenching experiments, it is shown that the energy of this triplet excited state is higher than 35 kcal/mol, in accord with the relatively large singlet oxygen quantum yield (Φ(Δ) = 0.25). However, in aqueous media, the coumarin triplet was no longer observed, and instead of that, a long-lived (160 μs in air-equilibrated solutions) free radical cation with a maximum absorbance at 370 nm was detected. The free radical cation generation, which has a quantum yield of 0.2, occurs by electron photoejection. Moreover, density functional theory (DFT) calculations indicate that at least 40% of the electronic density is placed on the nitrogen atom in aqueous media, which explains its lack of reactivity toward oxygen. On the other hand, rate constant values close to the diffusion rate limit in water (>10(9) M(-1) s(-1)) were found for the quenching of the C(314) free radical cation by phenolic antioxidants. The results have been interpreted by an electron-transfer reaction between the phenolic antioxidant and the radical cation where ion pair formation could be involved.     

The Reduced Basis Method for Time-Harmonic Maxwell's Equations

The Reduced Basis Method (RBM) generates low-order models of parametrized PDEs to allow for efficient evaluation of the input-output behaviour in many-query and real-time contexts. The RBM approach is decomposed into a time-consuming offline-phase, which generates a surrogate model and an online phase, which performs fast parameter evaluations. Rigorous and sharp a posteriori error estimators play a crucial role in the greedy process to generate the surrogate model and give bounds to the output quantities in the online phase. We show the theoretical framework in which the Reduced Basis Method is applied to Maxwell's equations arising from semiconductor interconnect structures and present first numerical results for model reduction in frequency domain. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An Approach to Shape Optimization with State Constraints

We introduce a new approach to solve shape optimization problems with state constraints. The problem is reformulated on a fixed reference domain using conformal pull-back. The shape dependence is then hidden in the conformal parameter. The problem is discretized using FEM and solved as an NLP. Finally the optimal shape can be reconstructed from the optimal conformal parameter. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The degenerate C. Neumann system I: symmetry reduction and convexity

The C. Neumann system describes a particle on the sphere S ⁿ under the influence of a potential that is a quadratic form. We study the case that the quadratic form has ℓ +1 distinct eigenvalues with multiplicity. Each group of m _σ equal eigenvalues gives rise to an O(m _σ )-symmetry in configuration space. The combined symmetry group G is a direct product of ℓ + 1 such factors, and its cotangent lift has an Ad*-equivariant momentum mapping. Regular reduction leads to the Rosochatius system on S ^ℓ , which has the same form as the Neumann system albeit for an additional effective potential.     

Measurement accuracy of a mono-fiber optical probe in a bubbly flow

The measurement accuracy of a mono-fiber optical probe is studied experimentally using isolated bubbles rising freely in a still liquid. The dwell time of the probe tip within the gas phase, which is obtained from both the optical probe signal and high-speed visualization, is compared with the value expected for a non-perturbed bubble. The difference originates mainly from the intrusive nature of the optical probe, which modifies the bubble behavior when it comes into contact with the probe tip. This interaction increases the dwell time if the bubble is pierced by the probe near its pole, and shortens it for piercing near the equator. The mean dwell time, obtained by averaging for various piercing locations, is shortened and the local void fraction indicated by the probe is thus underestimated. It is shown that the void fraction error can be correlated with a modified Weber number, and this correlation is helpful for sensor selection and for uncertainty estimate. In addition, the distribution of gas dwell time usually differs from the response expected for an ideal probe. This deviation results from the dependence of the dwell time error on the piercing location. The dwell time distribution can be used to infer the dependence of the dwell time on the piercing location. Finally, the deformation of long fibers during the bubble-probe interaction significantly increases the measurement error. Observed results are consistent with data of Andreotti (2009), which were measured in an airlift flow, suggesting that present results are applicable also to the case of moving liquid. Conclusions of this study could be applied also to conductivity probes or more generally to the interaction of a bubble with any kind of thin, intrusive sensor or fiber.     

Baryon form factors in chiral perturbation theory

We analyze the electromagnetic form factors of the ground state baryon octet to fourth order in relativistic baryon chiral perturbation theory. Predictions for the charge radius and the – transition moment are found to be in excellent agreement with the available experimental information. Furthermore, the convergence behavior of the hyperon charge radii is shown to be more than satisfactory. Received: 25 October 2000 / Published online: 23 January 2001     

Influence of the crystallite size on the phase transformation of yttria irradiated with swift heavy ions

The irradiation effects induced by swift heavy ions are now widely described in `bulk' materials. It is shown here that the behaviour of matter under irradiation depends on its crystalline state in the sense that a given material is all the more sensitive to swift heavy ion irradiations as the mean crystallite size L is small. The present paper relates the experimental results obtained in yttrium oxide from `in situ' X-ray diffraction measurements. Three kinds of sample have been irradiated: sintered samples (L = 1μm), non-ground powders (L = 45 nm) and ground powders (L = 28 nm). A cubic to monoclinic phase transformation appears if the electronic energy loss of the incident particle is higher than a threshold. The comparison between the different kinds of samples reveals that this phase transformation is all the easier as the mean crystallite size of the target is weak. Received 27 January 2000 and Received in final form 13 December 2000