scholarly journals Fractal Structure and Fractal Time in Silica Sol-Gels

1990 ◽  
Vol 180 ◽  
Author(s):  
James E. Martin ◽  
Jess Wilcoxon
Keyword(s):  
Light Scattering ◽  
Sol Gel ◽  
Silica Sol ◽  
Density Fluctuations ◽  
Gel Point ◽  
Decay Times ◽  
Fractal Time ◽  
Sol Gel Transition ◽  
Point Light ◽  
Gel Transition

ABSTRACTNear the gel point, light scattering studies of silica sol-gels reveal fractal clusters whose size diverges as a power law, in accord with the predictions of percolation theory. More surprising is the appearance of a fractal time description of the dynamics of these clusters. This novel dynamics has recently been revealed by quasielastic light scattering from the density fluctuations that occur at the sol-gel transition. Since the relaxation of fluctuations in these branched polymer systems is self-similar, decay processes occur on all time scales (fractal time), and average decay times diverge. An interpretation of this observation will be presented that relies on a length-scale-dependent viscosity and the geometrical self-similarity of the sol-gel transition. The scattering theory is extended to the calculation of time- and frequency-dependent viscoelastic properties, as well as mechanical properties such as the shear modulus, steady state creep compliance, and viscosity. The viscoelastic predictions are found to be in good agreement with experimental data.

The Pre-Gelation Phase Of Fibrin Aggregation

1981 ◽  
Author(s):  
P Wiltzius ◽  
G Dietler ◽  
W Känzig ◽  
A Haeberli ◽  
V Hofmann ◽  
...  
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Sol Gel ◽  
Polymerization Process ◽  
Gel Point ◽  
Chain Model ◽  
Fibrinopeptide A ◽  
Model Calculations ◽  
Sol Gel Transition ◽  
Gel Transition

So far, fibrin aggregation in solution has been studied by either static or dynamic light scattering and the data analyzed using a linear chain model. In the present study we have combined static and dynamic light scattering and compared the data with a model predicting a sol-gel transition. Fibrinogen solutions (cone. 2 mg/ml, Tris-NaCl buffer 0.15 M, pH 7.4) were incubated at 20°C with small amounts of Reptilase or thrombin, extending the polymerization process to 4-6 hours. The scattered intensity and correlation function were recorded for scattering angles 30° ≤ θ ≤ 150°. The measured data were compared with model calculations based on the Flory-Stockmayer distribution which predicts a sol-gel phase transition. This distribution is determined by a parameter λ indicating the extent of aggregation, λ = 0 corresponding to the monomeric solution and λ = 1 indicating sol-gel transition. Good agreement could be found for 75 nm long monomeric units aggregating: a) end-to-end for the beginning of the aggregation (0 0.3) and b) in a staggered overlap pattern as proposed by Ferry for the progressing polymerization (0.3 ≤ λ < 1). Prior to the gel point (λ = 1) no systematic difference was observed between the data obtained after activation with thrombin which splits both peptides A and B from fibrinogen and Reptilase which exclusively liberates fibrinopeptide A. This confirms that the release of fibrinopeptide A is the essential prerequisite for the aggregation process.

Time-Resolved Small Angle X-Ray Scattering and Dynamic Light Scattering Studies of Sol-Gel Transition in Gelatin

1988 ◽  
Vol 143 ◽  
Author(s):  
Dan Q. Wu ◽  
Benjamin Chu
Keyword(s):  
Light Scattering ◽  
Cross Section ◽  
Sol Gel ◽  
Slow Mode ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Saxs Intensity ◽  
Sol Gel Transition ◽  
Gel Transition

AbstractStructural and dynamical properties of an aqueous gelatin solution (5 wt%, 0.1M NaCi, pH=7) in a sol-gel transition were studied by time-resolved small angle x-ray scattering (SAXS) and dynamic light scattering (DLS) after quenching the gelatin sol at ∼45”C to 11°C. SAXS intensity measurements suggested the presence of gel fibrils which grew initially in cross-section. The average cross-section of the gel fibrils reached a constant value after an initial growth period of ∼800 sec. Further increase in SAXS intensity could be attributed to the increase in the length of the gel fibrils. Photon correlation, on the other hand, clearly showed two relaxation modes in both the sol and the gel (∼1 hr after the quenching process) states: a fast cooperative diffusion mode which remained constant from the sol to the gel state after correction for the temperature dependence of solvent viscosity; and a slow mode that could be attributed to the self-diffusion of the “free” gelatin chains and aggregates. The slow mode contribution to the time correlation function was reduced from ∼40% in sol to ∼20% in gel signaling a decrease but not the elimination of “free” particles in the gel network. The decrease in the intensity contribution by the slow mode is, however, accompanied by a large increase in the characteristic line-width distribution.

Dynamic light scattering study of the sol-gel transition

1991 ◽  
Vol 24 (26) ◽  
pp. 6839-6842 ◽  
Author(s):  
Liqi Fang ◽  
Wyn Brown ◽  
Cestmir Konak
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Sol Gel ◽  
Scattering Study ◽  
Sol Gel Transition ◽  
Gel Transition

Scaling Behaviour of the Viscoelastic Properties of a Biopolymer System Near the Gel Point

1989 ◽  
Vol 177 ◽  
Author(s):  
M. A. V. Axelos ◽  
M. Kolb
Keyword(s):  
Steady State ◽  
Percolation Theory ◽  
Viscoelastic Properties ◽  
Sol Gel ◽  
Oscillatory Shear ◽  
Gel Point ◽  
Rheological Measurements ◽  
Scaling Behaviour ◽  
Sol Gel Transition ◽  
Gel Transition

ABSTRACTRheological measurements have been performed on pectin-calcium systems close to the sol-gel transition. Two different experimental setups - steady state and oscillatory shear measurements - show scaling of the viscoelastic properties. The results of both types of measurements are consistent with each other and with scalar percolation theory.

Sol-Gel Transition Kinetics of Konjac Glucomannan Dilute Solution by Fluorescence Technique

2011 ◽  
Vol 399-401 ◽  
pp. 1326-1329
Author(s):  
Dong Ying Xu ◽  
Zheng Fu Liao ◽  
Hui Wang
Keyword(s):  
Chemical Engineering ◽  
Drug Carrier ◽  
Sol Gel ◽  
Konjac Glucomannan ◽  
Gel Point ◽  
Pharmaceutical Chemical ◽  
Dilute Solution ◽  
Sol Gel Transition ◽  
Kinetics Of ◽  
Gel Transition

Konjac glucomannan (KGM) has been widely used in pharmaceutical, chemical engineering, food industry, drug carrier delivery, etc. The sol-gel transition kinetics of KGM dilute solution was studied by steady fluorescence spectroscopy in this article. The results showed that the gel point of KGM solutions depend on the concentration of KGM, pH value and temperature. The sol-gel phase transition activation energy, ΔE, was calculated to be 83.1 kJ/mol based on first reaction kinetic model.

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