Switching behavior of thermochromic copper and silver tetraiodomercurate embedded in silica hybrid materials

• Composites based on silver and copper tetraiodomercurates were investigated.
• Switching properties of thermochromic compounds are modified due to interactions.
• Interactions between CTAB and thermochromics change the crystalline structure.
• The hysteresis phenomenon was evidenced for all thermochromic composites.
• Thermal stability of the compounds was enhanced after embedding in silica hybrids.

Thermochromic silica hybrids containing copper or silver mercuric iodides and cetyltrimethylammonium bromide (CTAB) were obtained and characterized. The color and switching behavior of the materials was studied in relationship with the structure of the thermochromic composites and silica network modifiers. In order to evidence the presence of the components and possible interactions governing the thermochromic transition, ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis – DR), Fourier transform infrared spectroscopy – attenuated reflection (FTIR-ATR), X-ray diffraction spectroscopy (XRD) and X-ray fluorescence (XRF) analysis were performed. The dynamic behavior was studied by UV–Vis reflectance spectra, FTIR and differential thermal analysis (DTA) analysis. Results confirm that during the embedding of thermochromic compounds in silica hybrid matrices, in the presence of CTAB, some interactions are established between thermochromic compounds and CTAB. These interactions determine the parameters of thermochromic transition in all cases of thermochromic composites. Hysteresis during the repetitive heating–cooling cycles was also observed. Thermal stability of the thermochromic compounds was enhanced after embedding in silica hybrids.