Christian Jäger

Short and intermediate range order in glass : nuclear magnetic resonance probes of site connectivities and distances

Abstract We present results on the spatial distribution and connectivity of phosphate in silver iodidesilver phosphate glasses, as a function of silver iodide and silver oxide content. These results were obtained using several different nuclear magnetic resonance experiments which give selective signals for phosphorous atoms which are in spatial proximity to one another. Our data show that the silver iodide in these glasses acts to spread the phosphate chains apart, and that, in highly modified phosphates, a distribution of chain lengths exists, with chain lengths as short as two phosphate units.

Structure and ionic conductivity of sodium titanophosphate glasses

Abstract 50Na 2 O– x TiO 2 –(50− x )P 2 O 5 (with x =0, 5, 10, 15) glasses have been characterized by infrared spectroscopy, 31 P magic angle spinning nuclear magnetic resonance (MAS–NMR) and 31 P double-quantum (DQ) MAS–NMR. MAS–NMR spectra show that phosphate network depolymerization occurs when x increases. Infrared spectra indicate that titanium is incorporated as TiO 6/2 units. DQ MAS–NMR enables us to characterize the Q n , ij phosphate units. Their chemical shifts, measured on DQ MAS–NMR spectra, were used as constraints for the deconvolution of one-dimensional MAS–NMR spectra. It indicates the formation of diphosphate units bonded to sodium and titanium Q 1,1 (Na,Ti) , even at the lowest x value. A structural unit formed by the sequence –Q 2,22 (Na) –Q 2,21 (Na) –Q 1,2 (Na,Ti) –TiO 6/2 –Q 1,1 (Na,Ti) –Q 1,1 (Na,Ti) –TiO 6/2 can be proposed. The increase of conductivity and glass transition temperature with x is discussed from this structural model.

Two-dimensional nuclear magnetic resonance evidence for structural order in extruded phosphate glasses

Two-dimensional (2D) rotorsynchronized nuclear magnetic resonance spectra have been acquired for extruded metaphosphate-type glass. It is shown that a partial alignment of the tetrahedral chains along the extrusion direction (structural order) exists.

High-speed satellite transition 27Al MAS NMR spectroscopy

High-speed MAS gives a three-fold gain in resolution of the m↔m−1 (m=32 and −12) satellite transitions of I = 52 nuclei in polycrystalline samples compared with the conventional “central transition” spectroscopy. This is demonstrated using a standard high-field NMR spectrometer and samples of tieilite and mullite. Signals from four- and six-coordinated Al are separated completely, and rotational sidebands do not overlap. Different six- and four-coordinated Al species can be distinguished.

Fabrication of carbon/silica hybrid materials using cationic polymerization and the sol‐gel process

Silica particles with different morphology have been functionalized with carbon shells by different synthetic procedures. In the key step, the bare silica particles are functionalized by a specific cationic surface polymerization with furfuryl alcohol (FA). The polyfurfuryl alcohol (PFA)/silica hybrid particles have been also post-functionalized with maleic anhydride (MSA) by a Diels Alder reaction. Simultaneously occuring cationic polymerization of FA and sol-gel process with TEOS has been used for producing interpenetrating carbon-silica hybrid materials. The thermal transformation of the PFA component on silica into the carbon phase has been carried out under argon atmosphere in a temperature range from 700 °C to 900 °C. The influence of the former morphology of the silica on the homogenity of the resulting carbon layer is shown by zetapotential measurements and electron microscopic investigations.

Cationic polymerization of cyclohexyl vinyl ether within MCM-41 channels

Cationic polymerization of cyclohexyl vinyl ether (CHVE) within mesoporous, siliceous molecular sieves (MCM-41) yields novel MCM-41-polyCHVE host-guest hybrid materials. Initiation within the channel can be achieved by triphenylmethylium or bis(4-methoxyphenyl)methylium silanolate ion pairs, as well as by mobile acidic silanols to a certain extent. Generation of the carbenium ions on MCM-41 is investigated by a special UV/VIS technique. The structure of poly(vinyl ether) generated within the channels of MCM-41 depends on the mechanism of initiation as shown by means of solid state 13C{1H} and 29Si{1H} CP MAS NMR spectroscopy.

Fabrication of Chromophoric Xerogels by Synergistic Combination of Nucleophilic Aromatic Substitution and the Sol-Gel Process

The nucleophilic substitution of fluorine of aromatic compounds with n-aminoalkyl trialkoxysilanes and consecutive sol-gel process have been used for the fabrication of various chromophoric sol-gel materials. The displacement of the fluoro substituent of an activated aromatic molecule occurs by a primary or secondary amino group of (CH3O)3Si-(CH2)3-NHR [R- = H-; CH3-, (CH3O)3Si-(CH2)3-] in tetraalkoxysilane or alcohol as solvent and the sol-gel process can be carried in the same vessel. The HF formed is trapped by a tertiary amine and simultaneously serves as the catalyst for the sol-gel process. Various aromatic compounds have been checked for this purpose: 1-(4-fluorophenyl)-2-nitroethylene, 1-(4-fluorophenyl)-2,2-dicyanoethylene, 4-fluorobenzonitrile, 4-fluoronitrobenzene, 4,4′-difluorobenzophenone, 4,4′-difluorobenzil, 7,7′-difluorodibenzylideneacetone, tetrafluoro-p-benzoquinone, and 1,5-difluoro-2,4-dinitrobenzene. Mono and disubstitution has been studied by UV/Vis- and solid state NMR spectroscopy of the xerogels.

Structural analysis of the thermal conversion of metal chlorides into phosphate glasses

Abstract The conversion reaction of metal chlorides (NaCl, KCl, PbCl 2 , CdCl 2 ) into phosphate glasses is studied via a structural approach. The glass compositions are: Na: 8.5–15.4%; K: 7.4–13.2% ; Pb: 1.6–2.6%; Cd: 0.4–0.7%; Cl: 0.2–20.1%; P: 11.6–20.4%; O: 36.5–60.8% (at. mol%). 31 P magic-angle-spinning nuclear magnetic resonance and 31 P double quantum analyses are employed for determining the structural evolution of the phosphate network as function of the batch composition and the melting temperatures (700°C and 900°C). The Q 1 /Q 2 ratios, measured by 31 P spectrum deconvolution, are in accordance with the elemental analyses of the samples prepared at 700°C and 900°C. 23 Na magic-angle-spinning nuclear magnetic resonance shows the presence of sodium in the amorphous phases and in NaCl crystals in devitrified samples. Transfer of populations in double-resonance experiments (TRAPDOR) are also consistent with the hypothesis that there is no specific bonding of sodium to a particular Q n unit in the phosphate network.

Functionalization of silica particles towards cationic polyelectrolytes using vinylformamide and 1,3-divinylimidazolidin-2-one as monomers

The use of vinylformamide and 1,3-divinylimidazolidin-2-one, bisvinylethylene-urea (BVU). as well as of the poly(vinylformamide-vinylamine) copolymer (PVFA-co-PVAm) for silica surface functionalization has been investigated Various procedures such as grafting from, crosslinking surface polymerization, and post-functionalization of adsorbed PVAm chains have been experimentally applied The advantage of the different synthetic methods is discussed with regard to the resulting surface structure of the organic/inorganic hybrid materials.