Chemical and rheological investigations of the sol-gel transition in organically-modified siloxanes

Lacan, P.; Guizard, C.; Cot, L.

doi:10.1007/bf00491681

Cited by 13 publications

(21 citation statements)

References 15 publications

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“…The spectra were obtained from the Fourier transform of the free induction decays (FID), following a single p/2 excitation pulse and a dead time of 5 s. Proton decoupling was always used during acquisition of 7 Li spectra. Chemical shifts were determined using a LiCl 1 M aqueous solution as reference.…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…4,5 In spite of the fascinating electrochemical, biological, electrical, and optical properties of organic-inorganic hybrid materials resulting from the interpenetration of the two phases at the nanometric scale, 6 only few works concerning the rheological aspects of the sol-gel transformation of hybrids and nanocomposites have been reported. 7,8 Over the last decade, [9][10][11][12] we have investigated the structure and electrical properties of siloxane-poly(oxypropylene) nanocomposites, in which the organic and inorganic phases are bonded by urea bridges. These transparent and flexible materials belong to the family of ureasils which also includes siloxane-poly(oxyethylene) hybrids (originally synthesized to be used as protonic conductors 13 and in photochromic devices).…”

Section: Introductionmentioning

confidence: 99%

“…This illustrates the greater chemical affinity of lithium ions with carbonyl oxygen of urea groups compared with the ether-type oxygen of PPO. Furthermore, at this low doping level the amount of ion pairs (detected by FTIR) should be extremely low, since 7 Li NMR has not detected it.…”

mentioning

confidence: 98%

“…Quantitative information about the partition of different cation species present in the siloxane-PPO hybrid sols and gels was obtained from 7 Li NMR. 130 and PPO 4000 hybrid sols.…”

mentioning

confidence: 99%

“…All spectra show a broad band with several shoulders, corresponding to convolution of the resonance of different lithium species in the gelling system. In order to determine the nature of these species 7 Li NMR measurements were performed in reference samples (commercial PPO, water, ethanol and commercial urea) containing lithium perchlorate. The comparison between the spectra of the reference samples (not shown) and of the siloxane-PPO hybrids (Fig.…”

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confidence: 99%

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Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane–poly(oxypropylene) nanocomposites

et al. 2005

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The influence of lithium doping on the evolution of viscoelastic properties and structure during the gelation of siloxane-poly(oxypropylene) (PPO) nanocomposites has been studied. For several [O]/[Li] ratios (O being the oxygen of the ether-type), dynamic rheological measurements allowed us to follow the evolution of storage and loss moduli, complex viscosity and phase angle during gelation of Li + -doped hybrid sols. All samples exhibit a Newtonian viscous character in the initial step of the process and are progressively transformed into viscoelastic gels. The evolution of the rheological properties of these systems allowed us to determine the aggregation mechanisms of silicon species present in hybrid sols, which lead to sol-gel transformation: mass fractal growth and nearly linear growth at the beginning of gelation, and percolation at the final stage of the process. The influence of doping on the aggregation mechanisms depends on the polymer molecular weight: while for hybrids containing long polymer chains (M w = 4000 g mol 21 ) gelation occurs in the initial stages through diffusion-limited monomer-cluster aggregation (DLMCA) for all doping levels, this mechanism is only observed for hybrids containing short chains Li NMR and infrared spectroscopy, affect the aggregation mechanisms during gelation and the condensation degree of the siloxane phase in the final dried materials.

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Section: Experimental Techniquesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 98%

“…Quantitative information about the partition of different cation species present in the siloxane-PPO hybrid sols and gels was obtained from 7 Li NMR. 130 and PPO 4000 hybrid sols.…”

mentioning

confidence: 99%

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confidence: 99%

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Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane–poly(oxypropylene) nanocomposites

et al. 2005

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Nuclear Magnetic Resonance of Geological Materials and Glasses

Moran

Howe

2000

Encyclopedia of Analytical Chemistry

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This article concerns the application of nuclear magnetic resonance (NMR) spectroscopic techniques to the analysis of geological materials and glasses. It includes inorganic minerals and glasses, but does not cover soils and clay minerals to any extent. The first part presents an overview of solid‐state NMR experiments applicable to inorganic solids. The range of nuclei accessible by NMR and the particular requirements for obtaining good spectra of more difficult nuclei, including quadrupolar nuclei, are discussed. The experimental conditions under which solid‐state NMR can provide quantitative analytical measurements are also considered. NMR spectroscopy provides element‐specific speciation and structural information including coordination environment and bond distances. It is particularly valuable for the analysis of amorphous and partially crystalline materials not amenable to structure determination by X‐ray diffraction. NMR can detect and quantify materials containing multiple phases and can be used for in situ monitoring of phase transitions. It provides qualitative and quantitative speciation information for framework nuclei in glasses and is also capable of characterizing the dynamic behavior of mobile ions and solvent through relaxation, diffusion and chemical exchange experiments. Thus it has become an important technique for the study of hydrous minerals and gels and for ion‐conducting glasses. The sensitivity of NMR varies considerably, depending on the nucleus observed, its abundance and its chemical environment. NMR sensitivities and detection limits cannot compete with elemental analytical techniques such as X‐ray fluorescence. In addition, quantitation in solids requires careful control of experimental parameters and careful calibration to avoid artifacts. However, the selectivity of NMR as an analytical technique is unsurpassed and the development of specialist pulse sequences to measure specific local interactions in solids makes it particularly well suited to the analysis of geological materials and glasses. NMR imaging enables structural information to be resolved in three dimensions, although resolution in solid‐state imaging is limited to tens of micrometers at best owing to the broader line widths and lower signal‐to‐noise ratios compared with liquids. However, capabilities in this field are being extended all the time and the application of NMR imaging techniques in materials analysis is expanding steadily. An alternative to conventional imaging is NMR force microscopy, which shows potential for surface mapping at higher resolutions. The applications section is organized on the basis of the materials being analyzed. Within each section, NMR techniques are classified according to the observed nuclei. The emphasis is on more recent applications and on developments leading to enhanced resolution and sensitivity. Silicates and aluminosilicates represent the largest class of applications, followed by phosphate, borate and other oxide glasses. Sol–gel materials and the reactions leading to gel formation are also discussed, as are hydrous materials more generally. The other important areas of application reviewed are minerals, ceramics, high‐temperature melts and ion‐conducting glasses. Finally, the applications of NMR imaging in this field, although sparse at present, are potentially very great. This is illustrated by two major areas of application to date, namely the imaging of bone minerals and cement and concrete.

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Electrical Percolation During Gelation of Lithium Doped Siloxane-Poly(oxyethylene) Hybrids

Sacco

Dahmouche

Santilli

et al. 2004

J Sol-Gel Sci Technol

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Chemical and rheological investigations of the sol-gel transition in organically-modified siloxanes

Cited by 13 publications

References 15 publications

Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane–poly(oxypropylene) nanocomposites

Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane–poly(oxypropylene) nanocomposites

Nuclear Magnetic Resonance of Geological Materials and Glasses

Electrical Percolation During Gelation of Lithium Doped Siloxane-Poly(oxyethylene) Hybrids

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