Composition-Structure Relations in Organically Modified Silica Gels

1999 ◽  
Vol 576 ◽  
Author(s):  
Nicola Hüsing ◽  
Ulrich Schubert
Keyword(s):  
Silica Aerogel ◽  
Structural Parameters ◽  
Sol Gel ◽  
Silica Gels ◽  
Two Stage ◽  
Hydrolysis And Condensation ◽  
Unmodified Silica ◽  
Stage Process ◽  
Experimental Findings ◽  
Gel Network

ABSTRACTMonolithic silica aerogels modified by functional organic groups were prepared by basecatalyzed sol-gel processing of Si(OR)4 / R'Si(OMe)3 mixtures (R' = organofunctional group), followed by drying of the wet gels with supercritical CO2. When the functional organic group has only weakly or no basic properties, the microstructure of the obtained aerogels is similar to that of an unmodified silica aerogel prepared under the same conditions and quite independent of the kind of functional group. The experimental findings are explained by a two-stage process in which the R'Si≡ units condense to a pre-formed gel network obtained by hydrolysis and condensation of Si(OR)4. An increasing portion of R'Si(OMe)3 has the same effects on the hydrolysis and condensation reactions as decreasing the bulk density of an unmodified silica aerogel and the same structural consequences as increasing the water / silane ratio and the catalyst concentration acting on Si(OR)4. This leads to larger primary particles and, associated with that, smaller specific surface areas. The two-stage process is not observed when R' contains a strongly basic substituent such as NH2 or NHCH2CH2NH2. The structural parameters indicate that in these cases both R'Si(OMe)3 and Si(OR)4 are involved in the built-up of the gel network. This can be explained by extensive hydrogen bonding between the amino groups and silanol groups.

Sol-Gel Polymerization of Tetraalkoxygermanium and Organotrialkoxygermanium Monomers

1996 ◽  
Vol 431 ◽  
Author(s):  
Brigitta M. Baugher ◽  
Douglas A. Loy
Keyword(s):  
Chemical Modification ◽  
Sol Gel ◽  
Silica Gels ◽  
Germanium Oxide ◽  
Oxide Materials ◽  
Siloxane Bond ◽  
Mild Conditions ◽  
Condensation Reactions ◽  
Hydrolysis And Condensation ◽  
Opening Up

AbstractWhile the sol-gel polymerizations of tetraalkoxy- and organotrialkoxysilanes have been extensively studied, there have been few reports of similar investigations with the analogous tetraalkoxygermanium and organotrialkoxygermanium compounds. Germanium alkoxides have received less attention due, in part to their higher cost, but also their greater reactivity towards hydrolysis and condensation reactions. Germanium oxide materials are potentially interesting because the Ge-O-Ge linkage is labile (compared with the siloxane bond in silica gels and polysilsesquioxanes) opening up the possibility of further chemical modification of the polymeric architecture. This may permit hydrolytic reorganization of germanium oxide networks under relatively mild conditions. In this paper, we will present the results of our investigations of the solgel polymerizations of tetraethoxygermanium 1, tetraisopropoxygermanium 2, and methyltriethoxy-germanium 3 to afford network materials as both xerogels and aerogels.

Preparation of Silica Aerogels Monoliths from Hydrophobic Silica Gels and Pluronic10R5 via Sol–Gel Process

2020 ◽  
Vol 12 (2) ◽  
pp. 206-211
Author(s):  
Supattra Eangpayung ◽  
Supan Yodyingyong ◽  
Darapond Triampo
Keyword(s):  
Mass Loss ◽  
Propylene Oxide ◽  
Silica Aerogel ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Silica Gels ◽  
High Porosity ◽  
Hydrophobic Silica ◽  
Sol Gel Process ◽  
Poly Propylene

Silica aerogel, the most common type of aerogels, comprised of 95% air in its structure which made the aerogel has a high surface area, high porosity, low density, and low thermal conductivity. Because of its structure and high porosity, one of its major weakness compared to other materials is being very brittle. This study aims at strengthening the connection points between silica nanoparticles using Pluronic10R5 (poly(propylene oxide)8–poly(ethylene oxide)22–poly(propylene oxide)8) where the Pluronic10R5 was used to reduce phase separation during the silica condensation reaction in the sol–gel process. Silica aerogel monoliths were prepared via a sol–gel process from hydrophobic silica gels and Pluronic10R5 with an ambient pressure drying (APD) process. Results from the compression test showed that the Pluronic10R5/silica aerogels have improved mechanical property by ten times that of unmodified silica aerogels. A thermogravimetric analysis (TGA) showed a mass loss at 300–400 °C that is attributed to the surface methyl group, while a mass loss at 200 °C refers to the loss of Pluronic10R5 which confirms the incorporation of Pluronic10R5 into the monolith. Moreover, infrared (IR) images revealed that the top surface temperature of Pluronic10R5/silica aerogels monolith is about 80 °C differs from the bottom heat source temperature of 160 °C.

Velar softening

2020 ◽  
pp. 13-21
Author(s):  
Daniel Recasens
Keyword(s):  
Sound Change ◽  
Two Stage ◽  
Stage Process ◽  
Change Mechanisms ◽  
Equivalence Model ◽  
Experimental Findings

In so far as velar softening is a two-stage process involving velar palatalization and velar assibilation, it is claimed that these two sound-change mechanisms ought to be analysed separately. A distinction is made between front velar stop productions, and the (alveolo)palatal stop outcome of gestural blending between velar stops and front vocalic realizations. The chapter also presents and evaluates two general models of velar softening, i.e., the articulation-based model proposed by the Neogrammarians and the acoustic equivalence model proposed by Ohala and colleagues. Several arguments in support of the former model are presented, which are based on articulatory evidence and on experimental findings reported in earlier acoustico-perceptual studies.

Automation of Two-Stage Factor VIII Assay

1978 ◽  
Vol 39 (02) ◽  
pp. 455-465 ◽  
Author(s):  
Yvonne Stirling ◽  
D J Howarth ◽  
Marguerite Vickers ◽  
W R S North ◽  
T W Meade
Keyword(s):  
Factor Viii ◽  
Optical Density ◽  
Electric Circuit ◽  
Clotting Time ◽  
Two Stage ◽  
Laboratory Error ◽  
Premature Closure ◽  
Factor Viii Concentrates ◽  
Experimental Findings ◽  
Automated Methods

SummaryTwo automated methods for two-stage factor VIII assays have been compared with one another, and evaluated in practice. The Depex method records the clotting time when an electric circuit is completed by the formation of a fibrin thread across a hook-type electrode; the Electra method is based on an optical density technique of clot detection. The two methods gave comparable results for measured levels of factor VIII when haemophilic or “normal” plasmas were assayed. Results from the two methods in practice also suggest that both are valid at low and “normal” factor VIII levels. The Electra method is also probably suitable for assays of concentrates; however, the Depex method appears to give falsely high values in these circumstances, and experimental findings suggest that the reason may be that increased viscosity due to the high fibrinogen levels in factor VIII concentrates causes premature closure of the circuit between the two ends of the Depex electrode. The main advantage of the Depex method is that, provided 3 or 4 machines are available, a given number of assays can be completed more quickly than on Electra. The main advantages of Electra are that it is probably subject to less laboratory error than Depex, and that it is suitable for assaying concentrates as well as haemophilic and “normal” plasmas.

Hybrid Micro-Optical Sensors via Sol-Gel Soft Lithography

2000 ◽  
Vol 628 ◽  
Author(s):  
Mark A. Clarner ◽  
Michael J. Lochhead
Keyword(s):  
Optical Sensors ◽  
Soft Lithography ◽  
Sol Gel ◽  
Silica Gels ◽  
Ph Sensing ◽  
Ambient Conditions ◽  
Sensor Applications ◽  
Patterned Structures ◽  
Biological Functionality ◽  
Indicator Dyes

ABSTRACTOrganically modified silica gels and dye-doped silica gels have been patterned into micrometer-scale structures on a substrate using micro molding in capillaries (MIMIC). This approach is from a class of elastomeric stamping and molding techniques collectively known as soft lithography. Soft lithography and sol-gel processing share attractive features in that they are relatively benign processes performed at ambient conditions, which makes both techniques compatible with a wide variety of organic molecules, molecular assemblies, and biomolecules. The combination of sol-gel and soft lithography, therefore, holds enormous promise as a tool for microfabrication of materials with optical, chemical, or biological functionality that are not readily patterned with conventional methods. This paper describes our investigation of micro-patterned organic-inorganic hybrid materials containing indicator dyes for microfluidic sensor applications. Reversible colorimetric pH sensing via entrapped reagents is demonstrated in a prototype microfluidic sensor element. Patterned structures range from one to tens of micrometers in cross-section and are up to centimeters in length. Fundamental chemical processing issues associated with mold filling, cracking and sensor stability are discussed.

scholarly journals Two-Stage Biodiesel Synthesis from Used Cooking Oil with a High Acid Value via an Ultrasound-Assisted Method

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3703
Author(s):  
Ming-Chien Hsiao ◽  
Wei-Ting Lin ◽  
Wei-Cheng Chiu ◽  
Shuhn-Shyurng Hou
Keyword(s):  
Acid Value ◽  
Molar Ratio ◽  
Optimal Conditions ◽  
Two Stage ◽  
Cooking Oil ◽  
High Acid ◽  
Used Cooking Oil ◽  
Biodiesel Synthesis ◽  
Stage Process ◽  
Ultrasound Assisted

In this study, ultrasound was used to accelerate two-stage (esterification–transesterification) catalytic synthesis of biodiesel from used cooking oil, which originally had a high acid value (4.35 mg KOH/g). In the first stage, acid-catalyzed esterification reaction conditions were developed with a 9:1 methanol/oil molar ratio, sulfuric acid dosage at 2 wt %, and a reaction temperature of 60 °C. Under ultrasound irradiation for 40 min, the acid value was effectively decreased from 4.35 to 1.67 mg KOH/g, which was decreased to a sufficient level (<2 mg KOH/g) to avoid the saponification problem for the subsequent transesterification reaction. In the following stage, base-catalyzed transesterification reactions were carried out with a 12:1 methanol/oil molar ratio, a sodium hydroxide dosage of 1 wt %, and a reaction temperature of 65 °C. Under ultrasound-assisted transesterification for 40 min, the conversion rate of biodiesel reached 97.05%, which met the requirement of EN 14214 standard, i.e., 96.5% minimum. In order to evaluate and explore the improvement of the ultrasound-assisted two-stage (esterification–transesterification) process in shortening the reaction time, additional two-stage biodiesel synthesis experiments using the traditional mechanical stirring method under the optimal conditions were further carried out in this study. It was found that, under the same optimal conditions, using the ultrasound-assisted two-stage process, the total reaction time was significantly reduced to only 80 min, which was much shorter than the total time required by the conventional method of 140 min. It is worth noting that compared with the traditional method without ultrasound, the intensification of the ultrasound-assisted two-stage process significantly shortened the total time from 140 min to 80 min, which is a reduction of 42.9%. It was concluded that the ultrasound-assisted two-stage (esterification–transesterification) catalytic process is an effective and time-saving method for synthesizing biodiesel from used cooking oil with a high acid value.

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