Phase Change Materials Based on Mesoporous Silica

Thermal energy can be stored as sensible or latent heat. Phase change materials (PCMs) use latent heat storage, offering great energy density over a limited temperature range. Organic materials, such as paraffins, fatty acids, polymers, sugar alcohols and their eutectic mixtures can be used as PCMs for applications near room temperature, due to their high liquid-solid enthalpy. Inorganic salts and salts hydrates can also function as PCMs, although most of them suffer from incongruent crystallization. Pure PCMs exhibit some disadvantages, such as leakage, decreased thermal transfer and storage capacity during use, arising from their large change in molar volume upon phase transition. These drawbacks can be alleviated by impregnation in high porosity matrices. A promising class of porous matrices is represented by Mesoporous Silica Nanomaterials (MSN). MSN offer high pore volume and surface area, often in excess of 1 cm3/g and 1000 m2/g, respectively, monodisperse pores, high chemical and thermal stability and ease of tailoring their textural, morphological and surface properties through chemical synthesis. To date, the studies on nanocomposites phase change materials using mesoporous silica matrices have not been reviewed. The current review focuses on the various strategies for obtaining the MSN matrices and PCMs, their properties and the fundamental aspects pertaining to the difference in thermal properties between nanoconfinement in MSN and bulk. The monodisperse pores in the 2 – 50 nm range give rise to nanoconfinement effects, such as decreased melting and crystallization points with respect to bulk phases, hysteresis between melting and crystallization and existence of an interface, liquid-like layer between the silica surface and PCM molecules. The nanoconfinement effects on the PCM properties are discussed and insight into the materials and their applications is provided. Keywords: Phase change, mesoporous silica, shape-stabilized, form stable, nanoconfinement, heat storage, nanocomposites.