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Superporous Hydrogel Composites: A New Generation of Hydrogels with Fast Swelling Kinetics, High Swelling Ratio and High Mechanical Strength
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Kinam Park, Jun Chen, Haesun Park
Hydrogels can be prepared in the presence of gas bubbles. In this technique the monomers are polymerized or water-soluble polymer chains are crosslinked around gas bubbles generated by a blowing agent. The gas-blowing technology has been widely used in the preparation of plastic foams from materials such as polyurethanes, rubber, and poly(vinyl chloride). The key ingredient in the foaming process is a blowing agent (or foaming agent), which is defined as any substance or combination of substances capable of producing cellular structure within a polymer matrix. Foaming agents are classified as; (a) physical foaming agents that expand when pressure is released (e.g., nitrogen and carbon dioxide) and (b) chemical foaming agents that decompose or react to form a gas (e.g., sodium bicarbonate in the presence of acid).
The primary responses to the initial risks: a “city machine” and its essential characteristics
Published in Vittorio Guglielmetti, Piergiorgio Grasso, Ashraf Mahtab, Shulin Xu, Mechanized Tunnelling in Urban Areas, 2008
Vittorio Guglielmetti, Piergiorgio Grasso, Ashraf Mahtab, Shulin Xu
Foam represents the physical state of a special liquid containing a surfactant (the foaming agent) in which air is dispersed so that it expands to enclose the air with a film (or membrane), thus forming bubbles of this liquid. The foam bubbles have an internal pressure higher than the atmospheric pressure; and the bubble pressure is related to the size of the bubble and the strength of the bubble membrane. Bubbles in a dry foam, in which the thickness of the layer has a relatively limited dimension, are not spherical, but are joined together in a polyhedral shape that is almost like a dodecahedron, with nearly planar membranes between the bubbles (Milligan, 2001, Fig. 4.9). The bubble’s properties are governed by the Foam Expansion Ratio, FER, the relationship between the foam’s and the original liquid’s volumes, and also by the nature and concentration of the foaming agent in the liquid. Another important parameter controlling the effectiveness of the conditioning is the Foam Injection Rate, FIR, the ratio between the volume of the injected foam and the volume of the treated soil.
Contemporary Machining Processes for New Materials
Published in E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan, Remanufacturing and Advanced Machining Processes for New Materials and Components, 2022
E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan
Selection of a chemical foaming agent is mainly determined by a processed polymer type. Some agents may be applied quite universally, like ADCA, while others are more specialized and dedicated to particular groups of plastics.
Rheology and printability of Portland cement based materials: a review
Published in Journal of Sustainable Cement-Based Materials, 2023
Uday Boddepalli, Biranchi Panda, Indu Siva Ranjani Gandhi
Surfactants or foaming agents are used commonly for the production of cellular structure in foam concrete and other CLSM. The cellular structure can be generated either based on pre-foaming method or mix foaming method. These foaming agents are basically powerful air entraining admixtures which aids in reduction of surface tension of water and facilitates air incorporation and stabilization. The characteristics of these surfactants (viscosity, adsorption, solubility and critical micelle concentration), are reported to effect the quality of foam generated to a greater extent [161–163]. The stability of the foam could also be improved by employing the foam stabilizers such as xanthan gum, carboxymethyl cellulose etc. [164–166]. Limited studies available on 3D printable foam concrete in this regard have proved that increase of surfactant dosage and the foam volume in foamed concrete leads to decrease in the yield stress and viscosity [69]. Despite above mentioned reduction, the thixotropy of foamed concrete was reported to increase with increase of foam volume [138].
Mechanistic study of nanoparticles–surfactant foam flow in etched glass micro-models
Published in Journal of Dispersion Science and Technology, 2018
Nurudeen Yekeen, Muhammad A. Manan, Ahmad Kamal Idris, Ali Mohamed Samin, Abdul Rahim Risal
Foam is a dispersion of gas in liquid, which is produced when a foaming agent containing liquid comes into contact with gases and enough mechanical energy is supplied, which causes the liquid to foam.[1,2] Foam has useful applications in numerous processes such as food industry, mineral floatation, firefighting, textiles processing, and personal-care products and enhanced oil recovery (EOR).[3456] However, the effective application of foams for all these processes is limited by the instability of the thin liquid films at the gas–liquid interface of foam. Foam is usually generated with surfactants, which serve as both the foaming and stabilizing agent. Foam stability is ensured by the adsorption of surfactant molecules at the foam lamellae.[7] However, surfactant-stabilized foam has a high tendency to coalesce due to the low energy of attachment of the surfactant molecules to the air–water interface of foam. Besides, surfactant-stabilized foam also suffers from the loss of surfactant molecules to the surface of the reservoir rocks and clay minerals, which reduces the available surfactant molecules that can adsorb at the air–water interface of the foam to stabilize the foam lamellae.[8]
Preparation of thermal insulation materials based on granite waste using a high-temperature micro-foaming method
Published in Journal of Asian Ceramic Societies, 2022
Mengbo Pan, Xiang Li, Xiaopeng Wu, Fei Zhao, Chengliang Ma
In general, inorganic lightweight thermal insulation materials are made from raw materials such as silica, alumina, fire clay [7], calcium silicate, kaolin, perlite, diatomaceous earth, expanded vermiculite, and aggregates [8]; moreover, they are prepared using the pore former method [9], organic foam dipping method [10], sol–gel method [11], freeze-drying method [12], and in situ decomposition methods [13,14]. Recently, the foaming method [15] has been extensively used for preparing porous materials and thermal insulation materials; a foaming agent is used to produce gas under high-temperature conditions, and these gases cannot be volatilized and wrapped in the material. Note that these pores are formed as the temperature drops [16]. Compared to the other methods, the sample prepared via the foaming method has smaller pores, and the ideal pore size can be obtained by changing the additional amount of foaming agent. The commonly used foaming agents include carbon-containing substances [17], aluminum nitride [18], silicon carbide [19], carbonate [20,21], and sulfate [22]. Yio et al. [23] used coal-fired power station furnace bottom ash and soda–lime–silica glass as raw materials and calcium carbonate as a foaming agent to prepare foam ceramics that can be used for thermal insulation and biological filters for water and wastewater treatment. Fuji et al. [24] thoroughly mixed cordierite ceramic powder and organic foaming agent and then used mechanical stirring in a nitrogen-protected atmosphere to fully foam the ceramic slurry. After drying and firing, the cordierite porous ceramics can be used for treating automobile exhaust gas. Li et al. [25] used calcium carbonate as the foaming agent to prepare closed-cell foam ceramics at 700–800°C, and the ceramic exhibited a high total porosity of 82%, high closed porosity of 78%, low density of 0.48 g/cm3, and compressive strength of 2 MPa. A lightweight ceramic tile with a porosity of 35% and an apparent density reduction of 26% was prepared by García-Ten et al. [26]; they used kaolin, quartz, and albite as raw materials with SiC as the foaming agent. Jiang et al. [27] prepared porous ceramics using granite as a raw material and SiC as a foaming agent; the porosity of the ceramic material was as high as 83.31%; however, the compressive strength of the material is relatively small (~0.85 MPa). Although the abovementioned research yielded good results, the prepared ceramic materials cannot be used as closed-cell refractory aggregates because of their high open porosity, low sintering temperature, or low strength, thus resulting in low refractoriness and poor high-temperature performance.