Preparation and characterization of SiO2-coated 2,4-hexadiyn-1,6-bis(ethylurea) microcapsules

A novel kind of time-temperature indicator, SiO2-coated 2,4-hexadiyn-1,6-bis(ethylurea) microcapsules, has been fabricated by coating SiO2 on 2,4-hexadiyn-1,6-bis(ethylurea). This kind of microcapsules is a model hydrophilic indicator, its stability is improved. And temperature-induced color change is irreversible even under varying irradiation. The influences of ammonia, tetraethyl orthosilicate(TEOS) and temperature on the product have been investigated. 2,4-Hexadiyn-1,6-bis(ethylurea) and the coated particles have been characterized by means of elemental analysis, mass spectrum, FTIR and Raman spectra and DSC, SEM, TEM and DLS analyses. The results indicate that 2,4-hexadiyn-1,6-bis(ethylurea)/SiO2 ratios, ammonia concentration and temperature could modulate the monodispersity and size of the microcapsules. The experiments indicate that when the molar ratio of 2,4-hexadiyn-1,6-bis(ethylurea)/SiO2/ammonia is 1:3:3.5 and temperature is 40 °C, the obtained microcapsules are well coated with the best monodispersity. Such sustained-release and hydrophilic microcapsules have very good prospects as a novel time-temperature chromatic indicator.