Macroporous aerogels

F. Placin, M. Feder, and F. Leal-Calderon Viscous Sintering Phenomena in Liquid-Liquid Dispersions Application to the Preparation of Sdicone Macroporous Aerogels. J. Phys. Chem. B 107, 9179 (2003). 

The pore size of aerogels varies. The International Union of Pure and Applied Chemistry classifies materials with pore sizes of less than 2 nm as micropores, 2-50 nm are called mesopores, and those greater than 50 nm in diameter are called macropores. While aerogels have some pores that fall within the micropore region, the majority of pores are in the mesopore region. 

Aerogels A special form of xerogel, from which the liquid has been removed in such a way as to prevent any collapse or change in the structure as liquid is removed (Iler). A gel with water-collapsible macropores as judged by direct porosimetry (Barby). 

Carbon (C)-aerogels have been investigated for one decade as a promising material for electrochemical applications in supercapacitors, fuel cells and waste water treatment [1,2], C-aerogels are nanoporous, electrically conducting and monolithic materials that provide the unique possibility to tailor the carbon properties on a molecular scale. The surface area and the degree of microporosity can be adjusted almost independently of the overall porosity for which mainly meso- and macropores are responsible. Whereas the mesostructure is determined by the stoichiometry of the reactants in the precursor solution, the pyrolysis conditions control the micropore structure of the material [3,4]. High pyrolysis temperatures will increase the electrical conduchvity [5], an important property for many electrochemical applications. 

The amorphous (nonordered) mesoporous materials such as ordinary SiC>2 aerogel and porous glass possess mesopores, but the channels or pores are irregular and the pore sizes distribute over a wide range. Most macroporous materials such as ceramics and cement have the same characteristics irregular pores and wide pore-size distribution. 

Aerojet has made organic aerogels with densities of 0.1-0.2 g/mL3 for use in insulators and capacitors.252 Transparent macroporous monoliths have also been made by polymerization of trimethylolpropanetrimethacrylate using toluene, ethyl formate, and other liquids as poro-gens.253 Poly(alkyl methacrylates) have good resistance to outdoor weathering and can be used in windows. 

Aerogels and Structure-Directed Mesoporous and Macroporous SoUds, 525... 

The alcogel featured in Figure 44.3 had a BET area of 641 m /g and a pore volume of 0.93 cm (liquid)/g. An even larger pore volume can be obtained if the fluid phase is removed under supercritical conditions to give an aerogel, that is, a product having a very low particle coordination number. Such materials are macroporous and have a high surface area (Table 44.1), but they are... 

Mulik S, Sotiriou-Ireventis C, Ireventis N (2(X)8) Macroporous Electrically Conducting Carbon Networks by I yrolysis of Isocyanate-Cross-Linked Resorcinol-Formaldehyde Aerogels Chem Mater 20 6985-6997... 

RF aerogels essentially display two types of pores voids between the polymer particles corresponding to meso- and macropores and voids inside the particles corresponding to micropores. The mesopore size strongly depends on the pH as pH... 

Mulik S, Sotiriou-Leventis C, Leventis N (2008) Macroporous Electrically Conducting Carbon Networks by Pyrolysis of Isocyanate-Cross-Linked Resorcinol-Formaldehyde Aerogels. Chem Mater 20 6985-6997. Tanaka S, Katayama Y, Tate M, Hillhouse H, Miyake Y (2007) Fabrication of continuous mesoporous carbon films with face-centered orthorhombic symmetry through a soft templating pathway. J Mater Chem 17 3639-3645. 

Baumann T, Satcher J (2004) Template-directed synthesis of periodic macroporous organic and carixm aerogels. J Non-Cryst Solids 350 120-125. 

---