China
Africa
Explore chapters and articles related to this topic
Electrochemical Sensors/Biosensors Based on Carbon Aerogels/Xerogels
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Liana Maria Muresan, Aglaia Raluca Deac
The sol-gel method was first used to prepare inorganic materials such as ceramics or glasses but it was rapidly extended to other materials such as oxides, organic compounds, etc. It consists in progressive hydrolysis and condensation reactions of molecular precursors in a liquid medium in the presence of a catalyst (Brinker and Scherer 1990). Precursors used in sol-gel processing are metallic salts, alkoxides, organic precursors (formaldehyde, resorcinol, melamine, polyacrilonitrile, etc.) which can be solved in water or in different organic liquids. Gelation implies the transformation of a sol to a gel and can be strictly controlled by the factors affecting the process (precursor/catalyst molar ratios, solvent nature, working temperature, etc.). Gels are often aged in the mother liquor, then they are washed and dried to obtain xerogels (by simple evaporation), aerogels (by supercritical drying) or cryogels (by freeze drier) (Job et al. 2005, Pajonk 1995).
Sol−Gel Processing
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
For single-component gels, colloidal particles are dispersed in water and peptized (dispersed) with acid or base to form a stable sol. The gelation can be achieved by (1) removal of water from the sol by evaporation to reduce its volume, or (2) changing the pH to reduce the stability of the sol in a controlled manner. High-silica glasses have been prepared by this route from fine SiO2 particles made by flame oxidation [13,14]. Aluminum alkoxides such as aluminum sec-butoxide and aluminum isopropoxide are readily hydrolyzed by water to form hydroxides. Which hydroxide is formed depends on the conditions used in the hydrolysis [15]. The initial hydrolysis reaction of aluminum alkoxides can be written as Al(OR)3+H2O→Al(OR)2(OH)+ROH
Biomaterials and Manufacturing Methods for Scaffolds in regenerative Medicine: Update 2015
Published in Gilson Khang, Handbook of Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine, 2017
Alginate originated from seaweed is composed of two repeating monosaccharides, L-guluronic acid and D-mannuronic acid. Repeating strands of these monomeric can be formed linear, water-soluble polysaccharides. Gelation occurs by interaction of divalent cations (e.g., Ca2+, Mg2+) with blocks of guluronic acid from different polysaccharide chains, as shown in Fig. 1.6. From this good gelation property, the encapsulation of calcium alginate beads impregnated with various pharmaceutics, cytokines, or cultured cells has been extensively investigated. Varying the preparation condition of gelation can control the structure and physicochemical properties. Calcium alginate scaffolds did not degrade by hydrolytic reaction, whereas they can be degraded by a chelating agent such as ethyleneamine tetraacetic acid (EDTA) or by enzyme. Also, the diffusion of calcium ions from an alginate gel can cause dissociation between alginate chains, resulting in a decrease of mechanical strength over time. One of the disadvantages of an alginate matrix is a potential immune response and the lack of complete degradation since alginate is not native to the human body.
Effects of high-concentration salt solutions and pH on swelling behavior of physically and chemically cross-linked hybrid hydrophobic association hydrogels with good mechanical strength
Published in Soft Materials, 2018
Shuling Gao, Guoqing Jiang, Bo Li, Peihui Han
In the petroleum industry, unwanted water production is a serious issue in oil- and gas-producing wells. One method of treating this problem is to chemically reduce unwanted water. There are chemical methods to deal with excessive water production, such as silicate (1), resins (2), and hydrogels (3). Among the chemical methods of plugging water with chemical materials, hydrogel treatment is a cost-effective method to improve sweep efficiency in reservoirs and to reduce excess water production during oil and gas production (4). From the point of view of the gelation mechanism, hydrogel treatment can be divided into in-situ gels and preformed particle gels. In-situ gel treatment is achieved by injecting an aqueous solution of polymer, crosslinker, and other additives into the reservoir, forming a hydrogel, hindering water production with time and temperature (5). Disadvantages of in-situ gel treament are the effect of formation water and adsorption on the cross-linking reaction and possible damages on the low permeability un-swept oil zone (6). Preformed particle gel treatment involves hydrogels being formed at surface facilities before injection and no gelation occurs in reservoirs, which overcomes some of the above-mentioned drawbacks of in-situ gels. Over the years, preformed particle gels have been applied economically to reduce water production in mature oilfields, and have achieved a good application effect (7). However, with the recent exploitation of deeper and hotter oil-bearing formations, the need has arisen for preformed particle gels that possess a good mechanical strength and can tolerate higher temperatures as well as higher salinity and hardness brines.
A review on multifunctional nanotechnological aspects in modern textile
Published in The Journal of The Textile Institute, 2022
Prashant D. Sarvalkar, Shubham D. Barawkar, Omkar S. Karvekar, Pandurang D. Patil, Saurabh R. Prasad, Kiran Kumar Sharma, Neeraj R. Prasad, Rajiv S. Vhatkar
Gelation: Gelation is the process of converting a free-flowing sol into a three-dimensional solid network that encloses the solvent medium. A gel is a liquid-rich semisolid. It's worth noting that liquid prevents the solid network from collapsing and the solid network from leaking. Gelation is most easily caused in the synthesis of nanomaterials by changing the pH of the reaction fluid. The number of cross-links in the network has a significant impact on the mechanical state of the gel. It is self-evident that the more cross-linking there is, the stiffer the structure becomes (Chantarachindawong et al., 2012; Venkateswara Rao et al., 2017).
Environmentally friendly starch/alginate aerogels for copper adsorption from aqueous media. A microstructural and kinetic study
Published in Journal of Environmental Science and Health, Part A, 2023
María S. Lencina, Cristian M. Piqueras, Daniel A. Vega, Marcelo A. Villar, María C. del Barrio
Hydrogel formation was carried out by two different methods known as internal and external gelation.[8,15] On the one hand, internal gelation is based on the pH change occurring in a CO2 atmosphere.[20,21] In this sense, a pregel solution containing both biopolymers and the crosslinking agent was placed in cylindrical molds (6 mm diameter, 12 mm length) located inside a high-pressure cell. When CO2 achieves the saturation pressure, pH decreases because of the carbonic acid production and the gelation process starts. The resultant acid media is responsible for the release of Ca2+ ions from the carbonate salt. Internal gelation is a kinetically controlled process where no diffusive effects are present. The resultant hydrogel presents a homogeneous structure. Calcium carbonate was used as alginate crosslinking agent (3.64 mmol per gram of alginate).[21] Pregel mixtures were treated with 50 ± 1 bar gaseous CO2 at room temperature for 48 h, in a high-pressure cell. Two depressurized rates were studied, 10 bar/min and 50 bar/min. On the other hand, external gelation consists in dripping the pregel in the crosslinking solution where Ca2+ is freely available, and thus hydrogel beads are instantly formed.[26,27] This process is completely diffusive; hence, the external surface rapidly gels, but inside the beads, the gelation follows a radial time-dependent process. Calcium chloride was used as alginate crosslinking (3.64 mmol per gram of alginate) and the beads obtained were kept submerged with magnetic stirring for 48 h to ensure complete gelation. Later, hydrogel beads (5 mm in diameter) were carefully washed with distilled water.