Response of inverse-opal hydrogels to alcohols

A polyacrylamide inverse-opal hydrogel (IOHPAM) film was synthesized by in situ polymerization in a polystyrene colloidal crystal template. The IOHPAM has a periodically ordered interconnecting porosity that endows the film with a band gap and structural color. The IOHPAM film exhibits a rapid reversible change in volume and in refractive index in response to alcohols and, consequently, the structural color and reflection peak of the IOHPAM film are quickly synchronized with these changes. The reflection peak of the IOHPAM film shows obvious blue or red-shifts that depend on the structure of the alcohols. The extent of the shift not only depends on the number of -OH groups, but also on the chain length, structure and concentration of the alcohols. The IOHPAM film is also sensitive to polyethylene glycol (PEG) and displays different blue-shift responses to PEGs with different molecular weights. Since the IOHPAM films have different reflectance spectra and structural colors in response to different types and concentrations of alcohols, this provides a potential way to visually detect alcohols.