A molecular-level understanding of the strain response of elastomers is a key to connect microscopic dynamics to macroscopic properties. In this study we investigate the local strain response of vulcanized, natural rubber systems and the effect of nanometer-sized filler particles, which are known to lead to highly improved mechanical properties. A multiplequantum NMR approach enables the separation of relatively low fractions of network defects and allows to quantitatively and selectively study the local deformation distribution in the strained networks matrix on the microscopic (molecular) scale. We find that the presence of nondeformable filler particles induces an enhanced local deformation of the matrix (commonly referred to as overstrain), a slightly increased local stress/strain heterogeneity, and a reduced anisotropy. Furthermore, a careful analysis of the small nonelastic defect fraction provides new evidence that previous NMR and scattering results of strained defect-rich elastomers cannot be interpreted without explicitly taking the nonelastic defect fraction into account.

The photoionization of the tris-2,2′-bipyridyl ruthenium(II) ion [Ru(bpy) 3 ] 2+ in water was investigated by laser-flash photolysis at 308, 355, and 532 nm up to very high excitation intensities I exc (500. . .900 mJ/cm 2 ). By single-pulse absorption and two-pulse luminescence measurements, it was established that the mechanism is cyclic and comprises three steps: excitation of [Ru(bpy) 3 ] 2+ to the metal-to-ligand charge-transfer (MLCT) excited state *[Ru(bpy) 3 ] 2+ , ionization of *[Ru(bpy) 3 ] 2+ by a second photon to give a hydrated electron e aq •and the oxidized complex [Ru(bpy) 3 ] 3+ , and photoreduction of [Ru(bpy) 3 ] 3+ by water. No other species is involved in the reaction. Experiments on chemically generated [Ru(bpy) 3 ] 3+ yield direct evidence for the photoreduction step and show that it is completed in less than 30 ns. The concentrations of [Ru(bpy) 3 ] 2+ , *[Ru(bpy) 3 ] 2+ , [Ru(bpy) 3 ] 3+ , and e aq•at the end of the laser pulse were measured as functions of I exc . Closedform expressions for these dependences were derived by a kinetic treatment. Very good simultaneous fits to the concentrations of all species were obtained with three global kinetic parameters only. A decision as to whether the photoreduction leads back to [Ru(bpy) 3 ] 2+ or to *[Ru(bpy) 3 ] 2+ is kinetically impossible in that system, but evidence pointing to a delayed generation of *[Ru(bpy) 3 ] 2+ by this reaction step is presented, which would also explain short-time anomalies of the luminescence reported in the literature. The quantum yield φ 2 of the photoionization step is the same at 308 and 355 nm, is independent of pH, and is an order of magnitude higher (0.016 ( 0.001) than previously thought. The quantum yield φ 3 of the photoreduction is comparable to φ 2 at pH 7 but lower by a factor of 14 at pH 0.

In spite of its model character, the mechanism of the photoionization described here has received very little attention. It is demonstrated that the electronically excited species *[Ru(bpy)3]2+ acts as a catalyst, and is regenerated in its excited state by a photoreaction of the ionized ruthenium complex [Ru(bpy)3]3+ with water (see catalytic cycle; bpy=2,2′‐bipyridine).

An instrument is described that allows the use of Fourier transform infrared (FTIR) spectroscopy as a detection system for kinetic processes after a pressure jump of up to 100 bars. The pressure is generated using a high performance liquid chromatography (HPLC) pump and water as a pressure transducing medium. A flexible membrane separates the liquid sample in the IR cell from the pressure transducing medium. Two electromagnetic switching valves in the setup enable pressure jumps with a decay time of 4 ms. The FTIR spectrometer is configured to measure time resolved spectra in the millisecond time regime using the rapid scan mode. All components are computer controlled. For a demonstration of the capability of the method first results on the kinetics of a phase transition between two lamellar phases of an aqueous phospholipid dispersion are presented. This combination of FTIR spectroscopy with the pressure jump relaxation technique can also be used for other systems which display cooperative transitions with concomitant volume changes.

We describe the design and performance of a pressure-jump instrument for time-resolved NMR experiments. Initial pressure of up to 250 bars can be produced by means of a HPLC pump and distilled water as a pressure-transmitting liquid. Fast pressure release at a time resolution of 3 ms is achieved using a fast acting valve driven by a piezostack close to the sample chamber. The pressure-jump cell is placed together with two valves in an especially designed NMR probe, which can be used in standard spectrometers with wide-bore magnets. All functions of the instrument are personal computer controlled. The equipment is designed for investigations on systems of biological interest, especially lipid-water dispersions. A theoretical consideration implies that probably the limited speed of valve opening determines the lower boundary of the jump time. The performance is illustrated by time-resolved NMR spectra across the phase transition of a phospholipid-water dispersion after a pressure jump from 100 bars to atmospheric pressure.