title: Three regimes of water adsorption in annealed silica opals and optical assessment.
abstract: Physisorbed and structurally bound (surface and internal) water in silica opals are distinguished and quantified by thermogravimetry. By controlled dehydroxylation with thermal annealing, we correlate these forms of water with the silica chemistry. In particular, we find that the silica capability to physically adsorb water from ambient moisture exhibits three regimes, associated with the distinct condensation behavior of bonded and unbonded surface silanols. Features in both opal IR absorbance and photonic band gap reproduce the physisorbed water regimes. This allows direct assessment of the water content and its evolution just by routine optical spectroscopy, being a useful tool for local and nondestructive analysis of colloidal silica. Besides, this provides a simple recipe for accurate tuning of the opal photonic band gap (about 10% in position and width) by just selecting the annealing temperature.
authors: Instituto de Ciencia de Materiales de Madrid, C/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain. francisco.gallego@icmm.csic.es
authors: Francisco
authors: F
authors: Gallego-Gómez
authors: Alvaro
authors: A
authors: Blanco
authors: Dolores
authors: D
authors: Golmayo
authors: Cefe
authors: C
authors: López
mesh_terms: D000327:Adsorption; D055620:Optical Phenomena; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D012822:Silicon Dioxide