Spectral response of sulfonated polystyrene photonic crystals with varying concentrations of ethanol

Abstract

Abstract Modifying polystyrene (PS) spheres through sulfonation is a well-established method to enhance their hydrophilic properties, rendering them valuable in diverse applications. Fabrication of photonic crystals (PCs) with sulfonated polystyrene (SPS) spheres offers an important platform for sensing applications. The hydrophilic nature of such PC platform helps in improving the detection of water content. In the present work, monodispersed SPS spheres were synthesized by adjusting the duration of the sulfonation reaction on the PS spheres created via emulsifier-free emulsion polymerization. PC opal films were fabricated using self-assembled PS and SPS spheres. The opal films were characterized using various techniques, including Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), angle-resolved reflection spectroscopy (ARRS), zeta potential and dynamic light scattering, and the results were compared and analysed. The hydrophilicity of the opal films was investigated using the water contact angle measurement, and it was found to improved by sulfonation. The spectral response of the PC opal films was investigated by monitoring Bragg’s diffraction spectra from the films using UV–VIS spectrometer. As a demonstration of a specific application, the prepared PC opal films were used to measure the water content in ethanol. PS and SPS opal films exhibited a noticeable blue shift in their spectral response when the water content in ethanol was increased to 3.8% and 3.4%, respectively. The added hydrophilicity brought on by the attached sulfonic groups improved the SPS film’s sensitivity to the water in the ethanol. SPS spheres demonstrated an optical response over a significantly more extensive range of the water content in ethanol than PS, which has a limited response range of up to 50%. Sulfonating PS spheres enhances colloidal stability and minimizes the tendency for aggregation in solution. Sulfonation for more than 3 h is found to exhibit reduced mechanical strength. Though the sulfonation induces an increase in surface roughness, the quality of the ordered arrangement of the spheres remained the same in comparison with PS films. By taking advantage of SPS’s hydrophilicity, high reactivity, stability, and the possibility of attaching additional functional groups, the present study opens up new possibilities for sensing water content in ethanol.