Exceptionally Large and Controlled Effect of Negative Thermal Expansion in Porous Heterogeneous Lyophobic Systems

Negative thermal expansion (NTE) is the process in which a system decreases its size upon heating and increases it upon cooling. NTE effect is unusual and useful for a great number of practical applications in the fields of electronics, medicine, mechanics, etc. In this work, NTE effect is experimentally investigated for three porous Heterogeneous Lyophobic Systems (HLS), associating water and two grafted mesoporous silicas or the microporous metal–organic framework ZIF-8. Considerable NTE effect, more than 1 order of magnitude higher than best-known materials, is observed for these systems. Additionally, it is demonstrated that for HLS, the temperature range in which NTE takes place is easily controlled by basic characteristics of the porous solid such as pore size distribution.