Mesoporous Hydrogels: Revealing Reversible Porosity by Cryoporometry,X-ray Scattering, and Gas Adsorption
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 12, 10158-10164 p.Article in journal (Refereed) Published
Mesoporous poly(2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) networks, with cross-linkercontents ranging from 100 to 5 mol %, were prepared using a hard-templating approach. The imbibition of the silicapellets with a monomer/cross-linker mixture resulted in mesoporous gels with a pore size of ~10 nm, which correspondswell with the average size of the fumed silica particles (10-11 nm). The highly cross-linked materials showed permanentsurface areas of up to 230m2 g-1 and porosities up to ~33 vol %. The porosity of the hydrogels was investigated in bothdry and water-saturated state by nitrogen sorption, cryoporometry, and small-angle X-ray scattering (SAXS). It is onlypolymeric materials that contain 50 mol % or more of the cross-linker that showed a significant porosity afterevaporative drying. Freeze-drying is able to preserve the porosity also for hydrogels of intermediate cross-linker content,but the pores of the materials of low cross-linker content collapses completely upon solvent removal. The observedcritical cross-linker ratio for pore stability compared favorably with a simple estimate of the critical cross-linker densityneeded to make the material sufficiently stiff to withstand the Laplace pressure during solvent removal. Analysis of thehydrogels in the water swollen state revealed that gels having cross-linker contents down to 5 mol % still possessedmesoporosity. The pores got less defined at very low cross-linker contents, while their size was rather constant atintermediate to high cross-linking densities. Closed pores could be reopened upon swelling, which suggests that theobserved pore collapse upon drying may be at least partly reversible.
Place, publisher, year, edition, pages
Washington, DC: American Chemical Society , 2010. Vol. 26, no 12, 10158-10164 p.
Mesoporous Hydrogels, Cryoporometry
Research subject Materials Chemistry
IdentifiersURN: urn:nbn:se:su:diva-46201DOI: 10.1021/la100290jOAI: oai:DiVA.org:su-46201DiVA: diva2:372047