Fractal Growth During Gelation

1992 ◽  
Vol 271 ◽  
Author(s):  
Edward J. A. Pope
Keyword(s):  
New Technology ◽  
Sol Gel ◽  
Silica Gels ◽  
Solution Viscosity ◽  
Fractal Growth ◽  
Index Changes ◽  
Sol Gel Transition ◽  
And Control ◽  
Gel Processing ◽  
Multi Component System

ABSTRACTSol-gel processing has emerged as an important new technology for the fabrication of a wide variety of glass, ceramic, and composite materials. In order to better understand and control the gelation process, a theoretical model has been developed which quantitatively links features of fractal growth with measurable properties of a solution during the sol-gel transition. The result of that effort is the fractal growth model of gelation (FGMG) which expresses the solution viscosity, light scattering, and refractive index changes as a funtion of time and the fractal dimension. In this paper, the application of FGMG to silica gels and multi-component system, such as titanium aluminosilicates, is presented.

scholarly journals Physical Interactions Strengthen Chemical Gelatin Methacryloyl Gels

Gels ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 4 ◽  
Author(s):  
Lisa Rebers ◽  
Tobias Granse ◽  
Günter Tovar ◽  
Alexander Southan ◽  
Kirsten Borchers
Keyword(s):  
Network Formation ◽  
Sol Gel ◽  
Solution Viscosity ◽  
Cross Linking ◽  
Physical Network ◽  
Helix Formation ◽  
Triple Helix Formation ◽  
Sol Gel Transition ◽  
And Control ◽  
Chemical Cross Linking

Chemically cross-linkable gelatin methacryloyl (GM) derivatives are getting increasing attention regarding biomedical applications. Thus, thorough investigations are needed to achieve full understanding and control of the physico-chemical behavior of these promising biomaterials. We previously introduced gelatin methacryloyl acetyl (GMA) derivatives, which can be used to control physical network formation (solution viscosity, sol-gel transition) independently from chemical cross-linking by variation of the methacryloyl-to-acetyl ratio. It is known that temperature dependent physical network formation significantly influences the mechanical properties of chemically cross-linked GM hydrogels. We investigated the temperature sensitivity of GM derivatives with different degrees of modification (GM2, GM10), or similar degrees of modification but different methacryloyl contents (GM10, GM2A8). Rheological analysis showed that the low modified GM2 forms strong physical gels upon cooling while GM10 and GM2A8 form soft or no gels. Yet, compression testing revealed that all photo cross-linked GM(A) hydrogels were stronger if cooling was applied during hydrogel preparation. We suggest that the hydrophobic methacryloyl and acetyl residues disturb triple helix formation with increasing degree of modification, but additionally form hydrophobic structures, which facilitate chemical cross-linking.

Effects Of Trioxane On Silica Gel

1990 ◽  
Vol 180 ◽  
Author(s):  
Xiaoming Li ◽  
P.F. Johnson
Keyword(s):  
Elevated Temperature ◽  
Surface Density ◽  
Sol Gel ◽  
Gelation Time ◽  
Silica Gels ◽  
Glass Transitions ◽  
Structure And Properties ◽  
Thermal Reactions ◽  
Sol Gel Transition ◽  
Gel Transition

ABSTRACTHydrolysis, condensation and thermal reactions of silica gels derived from TEOS with and without 1,3,5-trioxane (C3H6O3) were studied. Effects of trioxane on viscosity and gelation time of solutions were determined. Specific surface, density, porosity and microhardness of gels were measured. The behavior of gels at elevated temperature was clarified using DTA, TGA, and dilatometry. The properties and structure of trioxane containing sol/gels may be explained by the role trioxane played in the sol-gel transition. The results of this investigation concerning sol-gel/gel-glass transitions, structure and properties of gels are presented.

The Optical Behavior of Organic and Organometallic Molecules in Sol-Gel Matrices

1988 ◽  
Vol 121 ◽  
Author(s):  
B. Dunn ◽  
E. Knobbe ◽  
J. M. McKiernan ◽  
J. C. Pouxviel ◽  
J. I. Zink
Keyword(s):  
Rhodamine 6G ◽  
Sol Gel ◽  
Optical Gain ◽  
Luminescence Spectroscopy ◽  
Subsequent Aging ◽  
Organometallic Molecules ◽  
Sol Gel Transition ◽  
Optical Behavior ◽  
Gel Processing ◽  
Gel Transition

ABSTRACTThe low temperatures involved in sol-gel processing have enabled organic and organometallic molecules to be incorporated in gel matrices. These molecules serve as optical probes to characterize gel chemistry and structure. The present paper describes the use of luminescence spectroscopy to detail matrix rigidity effects and protonation/deprotonation reactions during the sol-gel transition and subsequent aging processes. In separate experiments, the addition of a laser dye, rhodamine 6G, has enabled us to demonstrate lasing and optical gain in a silica gel.

Hydrolysis of aluminium metal, synthesis of nano alumina and sol-gel processing of monoliths

2004 ◽  
Vol 848 ◽  
Author(s):  
M. Thiruchitrambalam ◽  
V.R. Palkar
Keyword(s):  
High Purity ◽  
Sol Gel ◽  
Purity Aluminium ◽  
Nano Alumina ◽  
High Purity Aluminium ◽  
Sol Gel Transition ◽  
Lower Temperature ◽  
Gel Processing ◽  
Hydrolysis Of ◽  
Aluminium Metal

ABSTRACTHigh purity alumina is usually prepared using various intermediate aluminium compounds such as aluminium nitrate, aluminium alkoxides etc., as precursors. In fact the above mentioned intermediate aluminium compounds themselves are produced from aluminium metal. The present investigation is concerned with examining the feasibility of using aluminium hydroxides prepared by hydrolyzing aluminium metal, for sol gel processing. The study assumes added significance in view of the claims of Alcoa that it is possible to produce high purity aluminium metal in large quantities economically.During the present investigation sols were prepared by using various hydroxides, ie., bayerite, gibbsite and boehmite. Sol gel transition was observed only in the case of boehmite sol and this was gelated by either forced gelation method to prepare powder or controlled gelation method to prepare monoliths.Transparent Xerogels (boehmite) could be prepared by controlled gelation method but the presence of a thin layer of bayerite often resulted in translucency. Crack free monoliths could be prepared by heating the xerogels at a low heating rate(< 1 °C/min). It was found that sol gel processed boehmite transformed to alpha alumina at a relatively lower temperature (∼ 1080 °C ) than the as prepared boehmite which transformed at about 1200 °C.

Contact Angle Measurement and Its Application To Sol-Gel Processing

1994 ◽  
Vol 346 ◽  
Author(s):  
D. J. Stein ◽  
A. Maskara ◽  
S. Hæreid ◽  
J. Anderson ◽  
D. M. Smith
Keyword(s):  
Contact Angle ◽  
Sol Gel ◽  
Dynamic Contact ◽  
Dip Coating ◽  
Contact Angles ◽  
Angle Measurement ◽  
Silica Gels ◽  
Solid Matrix ◽  
Surface Tensions ◽  
Gel Processing

ABSTRACTCapillary stresses during drying that result from the contact angle of a liquid solvent to a gel, surface tension, and pore size have an immense effect on the dried gel. The extent to which the gel shrinks is a balance between the capillary stress and the solid matrix strength. The dynamic contact angles and surface tensions of various solvents commonly employed in sol-gel processing on silica gels of various surface chemistries have been evaluated. A thin, dense coating of silica gel was formed by dip coating a standard glass slide in an acid catalyzed silica sol and drying. Some of the sample surfaces were organically modified. Dynamic contact angles were determined using a modified Wilhelmy plate technique. Solvent surface tensions were determined using the De Nouy ring technique. The bulk modulus of wet gels were determined with a three point bend experiment. We have found that contrary to previous investigators, who attributed different bulk densities obtained after drying from various alcohols to contact angles variations, gel shrinkage during drying is actually due to slightly different surface tensions and degrees of depolymerization of the gel network.

Base-Catalyzed Silica Gels: Structure and Chemistry

1990 ◽  
Vol 180 ◽  
Author(s):  
Garry J. Garvey ◽  
Bruce E. Smith
Keyword(s):  
Physical Properties ◽  
Mass Spectroscopy ◽  
Ammonium Carbonate ◽  
Sol Gel ◽  
Ammonium Hydroxide ◽  
Silica Gels ◽  
Pyrolysis Behavior ◽  
Enhanced Oxidation ◽  
Sol Gel Transition ◽  
Gel Transition

ABSTRACTThe chemical and physical properties of two base-catalyzed silica gels systems were characterized. The sol-gel transition was studied by titration, rheometry, and NMR. Pyrolysis behavior was monitored by TGA and mass spectroscopy. Many characteristics were strikingly similar for the two base-catalyzed systems. However ammonium hydroxide additions resulted in heterogeneities at lower concentrations than ammonium carbonate. Ammonium carbonate enhanced oxidation on pyrolysis.

Phase Separation in Alkoxy-Derived Silica System Containing Polyacrylamide

2007 ◽  
Vol 1007 ◽  
Author(s):  
Kousuke Kawamoto ◽  
Kazuki Nakanishi ◽  
Teiichi Hanada
Keyword(s):  
Phase Separation ◽  
Sol Gel ◽  
Secondary Phase ◽  
Nitrogen Adsorption ◽  
Silica Gels ◽  
Solvent Exchange ◽  
Scanning Calorimetry ◽  
Heat Treated ◽  
Sol Gel Transition

ABSTRACTBy inducing phase separation parallel to the sol-gel transition of alkoxy-derived silica systems, gels having both macroporous and mesoporous structures can be obtained. Using poly(acrylamide) (PAAm) as a phase-separation inducer, macro/mesoporous silica gels were synthesized. After solvent exchange by water, the size distribution of mesopores of wet gels was evaluated by thermoporometry using a differential scanning calorimetry (DSC). Alternatively, gels were evaporation-dried after solvent exchange by ethanol or water/ethanol, followed by heat-treatment to completely remove volatile and organic components. Characterization of the dried or heat-treated samples was carried out using a scanning electron microscope (SEM) and by nitrogen adsorption measurements. Experimental results showed that the interaction between PAAm and silica is not so strong as the case of polymers having poly(oxyethylene) chains. The contribution of the secondary phase separation within the crosslinking silica-rich phase was suggested to be responsible for the mesopore formation in the PAAm-silica system.

Engineering of Porosity in Amorphous Materials. Plasma Oxidation of Hydrocarbon Templates in Polysilsesquioxanes*

1994 ◽  
Vol 346 ◽  
Author(s):  
Douglas A. Loy ◽  
Richard J. Buss ◽  
Roger A. Assink ◽  
Kenneth J. Shea ◽  
Henry Oviatt
Keyword(s):  
Amorphous Materials ◽  
Oxygen Plasma ◽  
Sol Gel ◽  
Silica Gels ◽  
Oxygen Plasma Treatment ◽  
Plasma Oxidation ◽  
Inductively Coupled ◽  
Surface Areas ◽  
Bridging Groups ◽  
Gel Processing

ABSTRACTArylene- and alkylene-bridged polysilsesquioxanes were prepared by sol-gel processing of bis(triethoxysilyl)-arylene monomers 1-4, and alkylene monomers 5-9. The arylene polysilsesquioxanes were porous materials with surface areas as high as 830 m2/g (BET). Treatment with an inductively coupled oxygen plasma resulted in the near quantitative removal of the arylene bridging groups and a coarsening of the pore structure. Solid state 29Si NMR was used to confirm the conversion of the sesquioxane silicons (T) to silica (Q). The alkylene-bridged polysilsesquioxanes were non-porous. Oxygen plasma treatment afforded silica gels with mesoporosity. The porosity in the silica gels appears to arise entirely from the oxidation of the alkylene spacers.

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