title: Exploration and exploitation of water in colloidal crystals.
abstract: Water on solid surfaces is ubiquitously found in nature, in most cases due to mere adsorption from ambient moisture. Because porous structures have large surfaces, water may significantly affect their characteristics. This is particularly obvious in systems formed by separate particles, whose interactions are strongly influenced by small amounts of liquid. Water/solid phenomena, like adsorption, condensation, capillary forces, or interparticle cohesion, have typically been studied at relatively large scales down to the microscale, like in wet granular media. However, much less is known about how water is confined and acts at the nanoscale, for example, in the interstices of divided systems, something of utmost importance in many areas of materials science nowadays. With novel approaches, in-depth investigations as to where and how water is placed in the nanometer-sized pores of self-assembled colloidal crystals have been made, which are employed as a well-defined, versatile model system with useful optical properties. In this Progress Report, knowledge gained in the last few years about water distribution in such nanoconfinements is gathered, along with how it can be controlled and the consequences it brings about to extract new or enhance existing material functionalities. New methods developed and new capabilities of standard techniques are described, and the water interplay with the optical, chemical, and mechanical properties of the ensemble are discussed. Some lines for applicability are also highlighted and aspects to be addressed in the near future are critically summarized.
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, c/Sor Juana Inés de la Cruz 3, 28049, Madrid, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Gallego-Gómez
authors.forename: Alvaro
authors.initials: A
authors.lastname: Blanco
authors.forename: Cefe
authors.initials: C
authors.lastname: López
keywords: capillarity; colloidal crystals; nanoscale interfacial phenomena; self-assembled materials; water in porous materials; wet granular materials