The Role of Supercritical CO2 in the Drying of Porous Silicon (2008)
M. Bouchaour, N. Diaf, A. Ould-Abbas, M. Benosman, L. Merad and N-E. Chabane-Sari
Laboratoire de Matériaux & Energies Renouvelables (LMER), Faculté des Sciences, Université Abou Bekr Belkaïd, B. P 119, Tlemcen,13000, Algérie
The study of light emission from porous silicon has attracted great interest since the first observation of its photoluminescence at room temperature. Recently, particular interest is devoted to supercritical fluid CO2 applications on the drying of this semiconductor. This fluid is inotoxic, non-flammable, unreactive under most conditions, leaves no liquid waste. It has a potential to ameliorate environmental safety and health impact and it enables innovative processing technologies and material protection. This talk reviews the mechanism of supercritical drying of porous silicon and the role of this fluid in this process.
Key Words: Porous silicon � Supercritical drying � Supercritical fluid CO2
Impact of depressurizing rate on the porosity of aerogels (2011)
G. Amaral-Labat
a, A. Szczurek
a, V. Fierro
a, E. Masson
b, A. Pizzi
c, A. Celzard
a,d
a Institut Jean Lamour - UMR CNRS 7198, CNRS - Nancy-Université - UPV-Metz, Département Chimie et Physique des Solides et des Surfaces, ENSTIB, 27 rue Philippe Séguin, BP 1041, 88051 Epinal Cedex 9, France
b CRITT Bois, 27 rue Philippe Séguin, BP 91067, 88051 Epinal Cedex 9, France
c LERMAB - ENSTIB, 27 rue Philippe Séguin, BP 91067, 88051 Epinal Cedex 9, France
d Member of the Institut Universitaire de France, France
The effects of supercritical drying of diluted resorcinol-formaldehyde (RF) gels in CO2 and in acetone are compared. We show that, for both processes, depressurizing rate of the autoclave after drying has a significant influence on the resultant shrinkage, and hence on resultant bulk density, surface area and pore volumes. At depressurizing rates below 2 MPa/min, acetone leads to much lower shrinkage than does CO2, and is 1000 times cheaper. However, supercritical drying with CO2 remains interesting because it is faster, easier to control, less sensitive to the experimental conditions and cleaner. We indeed show that acetone is degraded and leads to various compounds that might partly remain in the porosity of the dried RF gels. Supercritical CO2 also clearly leads to the highest surface areas and micropore volumes, whereas supercritical acetone is in favour of higher mesopore volumes, especially at high depressurizing rates.
Key Words: Aerogel Supercritical drying Shrinkage
Pore volume Surface area
Poly(ethylene glycol) cryogels as potential cell scaffolds: effect of polymerization conditions on cryogel microstructure and properties (2009)
Yongsung Hwangab, Chao Zhangb, and Shyni Vargheseb
aMaterials Science and Engineering Program, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0418, USA
bDepartment of Bioengineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0412, USA
We report the synthesis and characterization of interconnected macroporous network structures of poly(ethylene glycol) (PEG) using cryogelation techniques. Novel monolithic networks containing a gradient of pore size in a layered fashion were created from a single precursor by manipulating their polymerization kinetics. Maintaining conditions that promote the rate of gelation compared to that of the nucleation of ice crystals leads to formation of either conventional hydrogel-like network structures or continuous heterogeneous networks containing layers of hydrogel-like and cryogel-like microstructures. In contrast, conditions promoting a faster rate of the nucleation of ice crystals compared to rate of gelation result in cryogels with a nearly homogeneous interconnected macroporous network. The rates of polymerization and nucleation of ice crystals were altered using a number of different parameters such as concentration of initiator, freezing temperature, and degree of supercooling. Compared to conventional hydrogels, the cryogels exhibit higher stress and strain at break; their mechanical and equilibrium swelling properties show a strong correlation with the network microstructure. Cell viability studies suggest no detrimental effect of these scaffolds on cell attachment and their distribution. Furthermore, a time dependent increase in chondrocyte proliferation was observed in cryogels over a long period of culture.
Structural characterisation of binary SiO2-TiO2 nanoparticle aerogels by X-ray scattering
(2009)
Emil Indrea1, Anca Peter2, Danut T Silipas1, Simina Dreve1, Ramona-Crina Suciu1, Marcela Corina Rosu1, Virginia Danciu2 and Veronica Cosoveanu2
1National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath, 400293 Cluj-Napoca, Romania
2Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, 11 Arany Janos, 400028 Cluj-Napoca, Romania
The effect of SiO2 to TiO2 aerogels content on their local structure is evidenced from X-ray scattering measurements. TiO2-SiO2 aerogels were prepared by sol-gel method followed by supercritical drying with liquid CO2 and heat treatment. The local structure of TiO2-SiO2 system was investigated by analysing the atomic pair distribution function PDF , G(r) , obtained from X ray scattering data The modified coordination radius values obtained for the first coordination spheres by addition of SiO2 denotes a diminution of the atom packing in this system. The PDF of the 3000C heat treated TiO2 aerogel sample shows well-defined features allowing an unambiguous structure search and refinement. In particular, the first peak in the PDF of the precursor phase is quite narrow and centered at about 1.9 Å, which is the Ti-O distance in Ti-O6 octahedra. This observation shows that well-defined Ti-O6 octahedra are already formed during the homogeneous precipitation stage of the chemical process. Inspecting the data from the analysis of the atomic pair distribution function G(r) one remarks the occurrence of Si-O pair as a first coordination formation at a distance of 1.49 Å and the interatomic distances at 2.18 Å for the first Si---Si and 3.58 Å for the second Si---Si bond.
Systematic studies of tannin-formaldehyde aerogels: preparation and properties (2013)
Gisele Amaral-Labat1,2, Andrzej Szczurek1,2, Vanessa Fierro1,2, Antonio Pizzi1,3 and Alain Celzard1,2
1 Université de Lorraine, ENSTIB, 27 rue Philippe Séguin, BP 1041, F-88051 Épinal Cedex 9, France
2 Institut Jean Lamour-UMR CNRS 7198, ENSTIB, 27 rue Philippe Séguin, BP 1041, F-88051 Épinal Cedex 9, France
3 LERMAB-EA 4370, ENSTIB, 27 rue Philippe Séguin, BP 1041, F-88051 Épinal Cedex 9, France
Gelation of tannin-formaldehyde (TF) solutions was systematically investigated by changing pH and concentration of TF resin in water. In this way we constructed the TF phase diagram, from which chemical hydrogels could be described, and also synthesized thermoreversible tannin-based hydrogels. Conditions of non-gelation were also determined. Hydrogels were dried in supercritical CO2 , leading to a broad range of TF aerogels. The latter were investigated for volume shrinkage, total porosity, micro-, meso- and macropore volumes, Brunauer-Emmett-Teller (BET) surface area, microscopic texture, mechanical and thermal properties. All these properties are discussed in relation to each other, leading to an accurate and self-consistent description of these bioresource-based highly porous materials. The conditions for obtaining the highest BET surface area or mesopore volume were determined and explained in relation to the preparation conditions. The highest BET surface area, 880 m2g-1 , is remarkably high for organic aerogels derived from a natural resource.
Key Words: aerogel, tannin, porosity, surface area, mechanical strength, thermal conductivity
Development of barley and yeast β-glucan aerogels for drug delivery by
supercritical fluids (2017)
Marta Salgadoa, Filipa Santosb,c, Soraya Rodríguez-Rojoa,*, Rui L. Reisb,c, Ana Rita C. Duarteb,c, María José Coceroa
a High Pressure Processes Group, Department of Chemical Engineering and Environmental Technology, EII Sede Mergelina, University of Valladolid, 47011 Valladolid, Spain
b 3B's Research Group- Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, 4805-017 Barco, Guimarães, Portugal
c ICVS/3B's - PT Government Associate Laboratory, Braga, Guimarães, Portugal
Polysaccharide aerogels are a good alternative as carriers for drug delivery, since they allow high loading of the
active compounds in matrices that are non-toxic, biocompatible and from a renewable feedstock. In this work,
barley and yeast β-glucans aerogels were produced by gelation in aqueous solution, followed by solvent exchange
and drying with supercritical CO2. First, viscoelastic properties and melting profile of the hydrogels were
determined. Then, the obtained aerogels were analyzed regarding morphology, mechanical properties and behavior
in physiological fluid. Both in the hydrogels and in the aerogels, big differences were observed between
barley and yeast ?-glucans due to their different chain structure and gelation behavior. Finally, impregnation of
acetylsalicylic acid was performed at the same time as the drying of the alcogels with supercritical CO2. The
release profile of the drug in PBS was analyzed in order to determine the mechanism governing the release from
the β-glucan matrix.
Key Words: β-glucan, Acetylsalicylic acid
Aerogel, Rheology, Supercritical drying,Supercritical impregnation
Tailored Network Formation in Graphene Oxide Gels (2018)Dorsa Parviza, Smit A. Shaha, Morgan G.B. Odomb, Wanmei Suna, Jodie L. Lutkenhausa,b, and Micah J. Greena,b
a Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, United States
a Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843, United States.
Harnessing Heat Beyond 200°C from Unconcentrated Sunlight with Nonevacuated Transparent Aerogels (June, 2019)Lin ZhaoLin Zhao, Bikram Bhatia, Sungwoo Yang, Elise Strobach, Lee A. Weinstein, Thomas A. Cooper, Gang Chen, and Evelyn N. Wang
Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States