Reversibly Thermoswitchable Two-Dimensional Periodic Gratings Prepared from Tethered Poly(N-isopropylacrylamide) on Silicon Surfaces

Abstract

In this study we used atom transfer radical polymerization to graft poly(N-isopropylacrylamide) (PNIPAAm) onto flat Si substrates. We then applied very large-scale integration and reactive ion etching sequentially to generate 200-nm-scale hole arrays of tethered PNIPAAm as two-dimensional periodic concave gratings (2DPCGs) on the Si surfaces. The hole array structures of tethered PNIPAAm could be created and erased reversibly at 25 and 40 °C, respectively, leading to significant changes in the effective refractive index (neff). The values of neff of the 2DPCGs were related to the depth of their holes generated after etching for various times, resulting in a color change from blue to red that could be observed by the naked eye at incident angles of 10-20°. Moreover, we used effective-medium theory to calculate the filling factors of air inside the 2DPCGs to verify the structural changes of the tethered PNIPAAm. Such designed 2DPCGs of thermorespective hydrogel films have potential applications in temperature-responsive optical devices [e.g., as antireflection structured surfaces (ARSs)] that operate at both visible and near-infrared wavelengths.

Fabrications and Applications of Stimulus-Responsive Polymer Films and Patterns on Surfaces: A Review

“…Grafted poly(methyl methacrylate) (PMMA) from a 200 nm-resolution hole array of photoresist on a silicon substrate as a pillar array of two-dimensional periodic relief grating (2DPRG) has been exploited to detect organic solvents in surrounding media, based upon the structural change of the 2DPRG as a consequence of the solvent induced reversible swelling/deswelling of PMMA chains, through an effective refractive index. Dramatic color changes, purple, green, yellow, and red, were observed with the naked eye when the surrounding media of PMMA-modified 2DPRG were acetone, tetrahydrofuran, dioxane, and chloroform, respectively (Figure 20b) [239,240]. …”

“…Photographic images demonstrate the grating effect of the 2DPRG under VOC exposing of chloroform, dioxane, THF, and acetone, from left to right. Reprinted from Reference [239] with permission.…”

Fabrication of device with poly(N-isopropylacrylamide)-b-ssDNA copolymer brush for resistivity study

“…The surface-initiated ATRP grafting of NIPAAm was performed in a glass vessel purged with N 2 . After that NIPAAm, PMDETA, Cu(I)Br, and CuBr 2 were dissolved in dimethylformamide (DMF) [ 5 , 21 ]. The reaction solution was sonicated for 2 min and then added to a glass vessel in which the AT/BIBB-functionalized wafers had been placed.…”

Identification of DNA single-base mismatches by resistivity of poly(N-isopropylacrylamide)-block-ssDNA copolymer brush films at dual temperatures

“…NIPAAm, PMDETA, CuBr, and CuBr 2 , were dissolved in dimethylformamide (DMF). 31,32 The solution was sonicated for 2 min, and added to AT/BIBBfunctionalized wafers. Polymerization was carried out at 25 C under N 2 for 4, 8, 12, 16, or 20 h. Then, the bromo-PNIPAAm-graed samples were removed from the solution and rinsed with copious amounts of deionized water to remove any unreacted monomer, followed by drying under a ow of N 2 at 25 C. Azido-PNIPAAm brushes were obtained on the surfaces aer treatment of bromo-PNIPAAm brushes with NaN 3 .…”