Physico-chemical control of sol–gel transition of titanium alkoxide-based materials studied by rheology

Ponton, Alain; Barboux-Doeuff, S.; Sanchez, C.

doi:10.1016/j.jnoncrysol.2004.08.243

Cited by 15 publications

(12 citation statements)

References 48 publications

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“…For the samples heated at 25 and 35 °C difference between the moduli is minimum; the predominance of G' over G´´is related the formation of partially hydrolyzed, low molecular weight aggregates, forming an incipient gel. For reversible (physical) gels, G' > G" in the gel point [29,30], thus it is possible to consider the material as close to the gel transition point at this temperature, For the samples heated at or above 45 °C the differences between G' and G" are more evident by almost one order of magnitude, showing the molecular evolution of the system in concordance with the FTIR results. The nitrate bridges as well as the mono and bidentate chelates formed ca.…”

Section: Viscoelastic Behaviorsupporting

confidence: 69%

FTIR studies of the thermo-reversible sol–gel transition of a titanium butoxide solution modified by nitrate ions

Vidales-Hurtado

Caudana-Campos

Mauricio-Sánchez

et al. 2021

J Sol-Gel Sci Technol

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A thermo-reversible sol-gel transition in solutions made of titanium n-butoxide, ethanol, water, and nitric acid is studied by in situ temperature-dependent Fourier transform infrared spectroscopy. Infrared spectra show that at temperatures departing from 45 °C, the nitrate ion substitutes the partially hydrolyzed butoxide ligands, by forming bridges and mono-and bidentate chelates. The exposed oxygen atoms in the nitrate ion favor the assembly between oligomers of low molecular weight through hydrogen bonds where water molecules work as binding agents, leaving to the gel formation. When the material returns to room temperature, the nitrate ion comes back to its free state, regenerating the sol. The suspension evolves with aging time from transparent to white, indicating the formation of TiO 2 particles, although the thermo-reversible effect is still observed upon heating. Infrared results suggest that gel formation proceeds through the same mechanism, however, the chelates and bridges occur through exposed Ti-OH moieties onto the particle surfaces. Additionally, after an aging period, a gel is formed at room temperature, that recovers the fluid state upon mechanical perturbation. In this case, TiO 2 particles join directly by week interactions such as hydrogen bonds. The dynamic rheological studies of the temperature-dependent viscoelastic behavior indicate that the elastic component is the most important in the material's structure.

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Section: Viscoelastic Behaviorsupporting

confidence: 69%

FTIR studies of the thermo-reversible sol–gel transition of a titanium butoxide solution modified by nitrate ions

Vidales-Hurtado

Caudana-Campos

Mauricio-Sánchez

et al. 2021

J Sol-Gel Sci Technol

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“…At this point both G ‘ and G ‘ ‘ can be scaled as a power law of the frequency: G ‘ ≈ G ‘ ‘ ≈ ω n . The experimentally determined scaling exponent n can be further related to the mass fractal dimension d f . , Muthukumar proposed the most complete relation for polydisperse polymeric fractals with full screening of the excluded volume near the gel point: where d = 3 for a 3-dimensional space.…”

Section: Methodsmentioning

confidence: 99%

Transitions in Structure in Oil-in-Water Emulsions As Studied by Diffusing Wave Spectroscopy

et al. 2006

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Transitions in structure of sodium caseinate stabilized emulsions were studied using conventional rheometry as well as diffusing wave spectroscopy (DWS). Structural differences were induced by different amounts of stabilizer, and transitions in structure were induced by acidification. Special attention was given to the sol-gel transition. In this study the criterion of the sol-gel transition being frequency independent was verified for emulsions using DWS. It was shown that this sol-gel transition did not correspond to the so-called ergodic-nonergodic transition. Differences, as a function of the pH, were found for emulsions containing different amounts of stabilizer. The emulsion droplets in an emulsion without extra stabilizer formed a continuous network upon acidification, while the droplets in emulsions with an excess of stabilizer formed a network of oil droplets at neutral pH. Upon acidification of the latter one, the initial network of oil droplets fell apart, and eventually a network of sodium caseinate, in which the oil droplets were embedded, was formed. This caused the appearance of two sol-gel transitions. The breaking of the initial network as well as the network formation of sodium caseinate in time was observed by DWS.

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“…SAOS tests are ideal for examining the linear viscoelastic properties of sols during gelation and vitrification, ,, allowing determination of all relevant material functions, including the complex modulus, G *, and complex viscosity, η*, which are given by eqs and , respectively. italicG * = italicG ′ + I G ″ η * = η ′ − i η ″ The elastic or storage modulus, G ′, is the amplitude of the portion of the stress wave that is in phase with the strain wave divided by the amplitude of the strain wave. It is a measure of the deformation energy stored by the sample during the shearing process.…”

Section: Resultsmentioning

confidence: 99%

“…Rheological Properties of the Sols. SAOS tests are ideal for examining the linear viscoelastic properties of sols during gelation and vitrification, 7,10,16 allowing determination of all relevant material functions, including the complex modulus, G*, and complex viscosity, η*, which are given by eqs 3 and 4, respectively.…”

Section: Resultsmentioning

confidence: 99%

Carbon Xerogel Microspheres and Monoliths from Resorcinol–Formaldehyde Mixtures with Varying Dilution Ratios: Preparation, Surface Characteristics, and Electrochemical Double-Layer Capacitances

et al. 2013

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Carbon xerogels in the form of microspheres and monoliths were obtained from the sol-gel polymerization of resorcinol and formaldehyde in the presence of potassium carbonate as catalyst, using water as solvent and two different molar dilution ratios. The objectives of this study were as follows: to investigate the effect of the dilution ratio, polymerization reaction time, and temperature on the rheological properties of the sols used to prepare the carbon xerogel microspheres and monoliths; and to determine the influence of their preparation methods and shapes on their surface characteristics and electrochemical double-layer (EDL) capacitance. An increase in the molar dilution ratio produced a decrease in the apparent activation energy of the sol-gel transition. Carbon xerogel microspheres were steam-activated at different burnoff percentages. The morphology, surface area, porosity, and surface chemistry of samples were determined. The main difference between the carbon xerogel microspheres and monoliths was that the latter are largely mesoporous. Better electrochemical behavior was shown by carbon xerogels in monolith than in microsphere form, but higher gravimetric and volumetric capacitances were found in activated carbon xerogel microspheres than in carbon xerogel monoliths.

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Physico-chemical control of sol–gel transition of titanium alkoxide-based materials studied by rheology

Cited by 15 publications

References 48 publications

FTIR studies of the thermo-reversible sol–gel transition of a titanium butoxide solution modified by nitrate ions

FTIR studies of the thermo-reversible sol–gel transition of a titanium butoxide solution modified by nitrate ions

Transitions in Structure in Oil-in-Water Emulsions As Studied by Diffusing Wave Spectroscopy

Carbon Xerogel Microspheres and Monoliths from Resorcinol–Formaldehyde Mixtures with Varying Dilution Ratios: Preparation, Surface Characteristics, and Electrochemical Double-Layer Capacitances

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