Polarity-indicative two-dimensional periodic concave gratings of tethered polystyrene on silicon surfaces for visualization in VOC sensing

In this study we generated two-dimensional periodic concave gratings (2DPCGs) of tethered polystyrene (PS) via fabrication processes, involving very-large-scale integration (VLSI) and reactive ion etching (RIE), on silicon substrate. Scale of ordered holes of the 2DPCG changed substantially after vapored cyclohexane, toluene, chloroform, tetrahydrofuran (THF), dichloromethane (DCM), acetone, ethanol, and water treatment as a consequence of the solvent induced reversible swelling–deswelling of PS chains. The structure change could be monitored by ellipsometry according to variations in effective refractive index (neff) and reflection of 2DPCG. A dramatic color displaying of dark purple, indigo, green-pink, bright yellow-red could be observed by naked eyes along an incident angle of 30° after exposing 2DPCG in the environments of acetone, cyclohexane, THF and toluene, respectively. Moreover, we calculated the filling factors of 2DPCG with effective-medium theory to evaluate the scale change degrees of the 2DPCG after these vapored solvent treatment. The described approach is facile and versatile in nature, which can be used for the fabrication of a variety of nanosensors based on the swelling–deswelling behavior of patterned polymer brushes.