A simple supramolecular crosslinked gel is reported with a photosensitive ruthenium bipyridine complex functioning as a crosslinker and poly(4-vinylpyridine) (P4VP) as a macromolecular ligand. Irradiation of the organogels in H2O/MeOH with visible and NIR light (in a multiphoton process) leads to cleavage of pyridine moieties from the ruthenium complex breaking the cross-links and causing degelation and hence solubilization of the P4VP chains. Real-time (RT) photorheology experiments of thin films showed a rapid degelation in several seconds, whereas larger bulk samples could also be photocleaved. Furthermore, the gels could be reformed or healed by simple heating of the system and restoration of the metal–ligand crosslinks. The relatively simple dynamic system with a high sensitivity towards light in the visible and NIR region make them interesting positive photoresists for nano/micropatterning applications, as was demonstrated by writing, erasing, and rewriting of the gels by single- and multiphoton lithography. 相似文献
We have investigated the free-radical copolymerization dynamics of styrene and divinylbenzene in the presence of micro- and macro-porogenic diluents in 100 μm I.D. sized molds under conditions of slow thermal initiation leading to (macro)porous poly(styrene-co-divinylbenzene) monolithic scaffolds. These specifically designed experiments allowed the quantitative determination of monomer specific conversion against polymerization time to derive the porous polymer scaffold composition at each desirable copolymerization stage after phase separation. This was carried out over a time scale of 3h up to 48 h polymerization time, enabling the efficient and repeatable termination of the polymerization reactions. In parallel, the porous and hydrodynamic properties of the derived monolithic columns were thoroughly studied in isocratic nano-LC mode for the reversed-phase separation of a homologous series of small retained molecules. At the optimized initiator concentration, polymerization temperature and time, the macroporous poly(styrene-co-divinylbenzene) monoliths show a permanent mesoporous pore space, which was readily observable by electron microscopy and indicated by nitrogen adsorption experiments. Under these conditions, we consistently find a polymer scaffold composition which suggests a high degree of cross-linking and thus minimum amount of gel porosity. These columns reveal a retention-insensitive plate height in the separation of small retained molecules which only slightly decreases at increased linear mobile phase velocity. As the polymerization progresses, a build-up of less-densely cross-linked material occurs, which is directly reflected in the observed consistent increase in retention and plate heights. This leads to a significant deterioration in overall isocratic separation performance. The decrease in performance is ascribed in particular to the increased mass transfer resistance governing the monoliths' performance over the whole linear chromatographic flow velocity range at polymerization times significantly higher than that of phase separation. The performance of the optimized monoliths only becomes limited by fluid dispersion due to the poorly structured macroporous pore space. 相似文献
Glass transition temperatures are reported for copolymers of acenaphthylene with the following comonomers: methyl meth-acrylate, styrene, maleic anhydride, diethyl maleate, N-vinyl-pyrrolidone, a-methylstyrene, and trans-stilbene. The data are discussed in terms of previously published treatments of the dependence of glass transition temperature on copolymer composition. The drop in glass transition temperature consequent upon incorporation of small quantities of comonomer is not related to the glass transition temperature of the corresponding homopolymer. 相似文献
The pharmacologically active [Ru(CO)(3)Cl(glycinate)] is shown to be in equilibrium with [Ru(CO)(2)(CO(2)H)Cl(glycinate)](-) (isomers) at around pH 3.1 which then at physiological pH reacts with more base to give [Ru(CO)(2)(CO(2))Cl(glycinate)](2-) (isomers) or [Ru(CO)(2)(CO(2)H)(OH)(glycinate)](-) (isomers). The ease with which [Ru(CO)(3)Cl(glycinate)] reacts with hydroxide results in it producing a solution in water with a pH of around 2 to 2.5 depending on concentration and making its solutions more acidic than those of acetic acid at comparable concentrations. Acidification of [Ru(CO)(3)Cl(glycinate)] with HCl gives [Ru(CO)(3)Cl(2)(NH(2)CH(2)CO(2)H)]. The crystal structures of [Ru(CO)(3)Cl(glycinate)] and [Ru(CO)(3)Cl(2)(NH(2)CH(2)CO(2)Me)] are reported. 相似文献
Scoliosis is the most common type of spinal deformity. In North American children, adolescent idiopathic scoliosis (AIS) makes
up about 90% of all cases of scoliosis. While its prevalence is about 2% to 3% in children aged between 10 to 16 years, girls
are more at risk than boys for severe progression with a ratio of 3.6 to 1. The aim of the present study was to test the hypothesis
that idiopathic scoliosis interferes with the mechanisms responsible for sensory-reweighting during balance control. 相似文献
A high-performance gel-permeation chromatography (HPGPC) column (7.5 mm I.D.), packed with a divinylbenzene cross-linked polystyrene gel (10 μm particles and 5 nm pore size) was used to produce a simple, one-stage clean-up procedure for determination of the insecticide hexaflumuron in three typical agricultural soils.
Conventionally, hexaflumuron extracts are purified by a series of time-consuming liquid-liquid partitions and solid-phase purification prior to high-performance liquid chromatography. HPGPC allows isolation of hexaflumuron from soil matrices with improved sensitivity in a shorter analysis time.
The use of HPGPC methodology has been validated over the range 0.01–1.0 mg/kg with recoveries in the range 73–119% (mean 98%). HPGPC gave excellent separation of hexaflumuron from other extracted materials with significant reduction in clean-up time and solvent consumption. This methodology has been successfully applied to samples derived from field trials. 相似文献
We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time. 相似文献