pH-Switchable Optical Properties of the One-Dimensional Periodic Grating of Tethered Poly(2-dimethylaminoethyl methacrylate) Brushes on a Silicon Surface

In this paper we used a novel fabrication process, involving very-large-scale integration and oxygen plasma treatment, to generate well-defined patterns of polymerized (2-dimethylaminoethyl methacrylate) (DMAEMA) as a one-dimensional periodic relief grating on silicon surfaces. The resolutions of the line patterns of the PDMAEMA brushes approached 400 nm. We describe an aqueous-based process controlled at a one-dimensional periodic grating. The line patterns of PDMAEMA brushes could generate water contact angles (WCAs) and refractive indices for TM and TE polarization on the surface because of one-dimensional binary periodic relief grating. The effective refractive index for TM polarization could be tuned between 1.18 and 1.28 upon increasing the pH from 2 to 12. The effective refractive index for TE polarization of the optical grating increased rapidly from 1.28 to 1.38 upon increasing the pH from 2 to 12; it returned to 1.29 after decreasing pH from 12 to 2. These reversibly tunable properties are created from a reversible pH-induced swelling transition of tethered PDMAEMA. In addition, the filling factors of the periodic grating were calculated to illustrate the conformational changes of tethered PDMAEMA in the binary grating. Such films, easily patterned by an inkjet printing technique, possess potential for pH-responsive biomaterial and membrane applications.