Swelling of polydimethylsiloxane in toluene solutions on electromagnetic resonance of metamaterials

A simple method for detecting organic solutions with a similar refractive index using metamaterials that are deposited on polydimethylsiloxane (PDMS) films is proposed. Pure toluene is diluted with pure alcohol for making up toluene solutions with concentrations of 0.5 wt. % and 1.0 wt. %. The experimental results from terahertz time-domain spectroscopy depict that pure alcohol and the toluene solutions have a similar refractive index in the terahertz region. The spectra of the metamaterials that are exposed to the toluene solutions are redshifted from that of the metamaterial that is exposed to pure alcohol, and the resonance frequencies of the metamaterials decrease with the increase in the concentrations of the toluene solutions. This result arises from the fact that the swelling of the PDMS films in the toluene solutions extends the arms of the split ring resonators, changing the dimensions of the metamaterials. The minimum detectable concentration of the metamaterials is less than 0.5 wt. % when they are exposed to the toluene solutions. The metamaterials deposited on the PDMS films can detect the organic solutions with a similar refractive index, and so they have the potential to sense organic gases with low concentrations.