Polymer spin coating The polymer Hydroxylase inhibitor was deposed on the external surface of the pSi by spin coating, in a manner that the polymer acts as a barrier to prevent the ingress of water into the porous matrix. PDEAEA was dissolved in toluene (40 mg/mL) and was spin-cast on the pSi film at 3,000 rpm for 1 min. Three deposition cycles were carried out on the same sample in order to generate a thick layer of polymer. The sample was placed under vacuum for 12 h, in order to evaporate the solvent remaining in the surface. Fourier transform infrared spectroscopy Fourier transform infrared (FTIR) spectroscopy was
performed with a Hyperion (Bruker) coupled to the liquid nitrogen cooled Mercury-cadmium-telluride (MCT) detector, in attenuated total reflectance (ATR) mode. Background spectra were taken in air and all spectra were recorded with an aperture size of 3 mm, over the range of 650 to 3800/cm, at a resolution of 22/cm averaging 64 scans. Interferometry reflectance spectroscopy Optical reflectivity spectra were obtained using an Ocean Optics USB2000 miniature fiber optic spectrometer (Ocean Optics, Inc, Dunedin,
FL, USA). Samples were illuminated with a tungsten lamp. buy PSI-7977 contact angle measurements Static water contact angles were measured both above and below the pK a of pDEAEA. For measurements, a 3-μL drop of Milli-Q water (Millipore, Billerica, MA, USA), below the pK a (pH 3 and pH 7) or above the pK a (pH 9), was placed on the surface of a dry sample at room temperature and an image was captured using a Panasonic WV-BP550/G CCTV Belnacasan camera (Panasonic, Kadoma, Osaka, Japan). The contact angles were analyzed using ImageJ (version 1.41) software. Results and discussion In order to design a pH-responsive polymer plug that acts as a barrier for water infiltrating into the pores of a pSi-based photonic film, poly(2-diethylaminoethyl acrylate) (pDEAEA) was chosen since the polymer’s pendant tertiary amine groups are deprotonated at pH > pK a (pK a of pDEAEA = 8.0) rendering the polymer hydrophobic . When the pH decreases
below the either pK a, the amino groups present on polymer are quaternized and the polymer becomes hydrophilic . Moreover, this polymer is not toxic and has been used in the past as a support for long-term human embryonic stem cell growth and pluripotency over a period of 2 to 6 months . Fabrication and characterization of pSi-pDEAEA films PSi single films were prepared from single-crystal highly doped p-type silicon wafers using a sine wave-modulated current density between 11.4 and 28.4 mA/cm2 resulting in a rugate filter with a reflectivity peak of 540.0 nm and a full width at half maximum (FWHM) of 30 nm . The porosity of the film was simulated from the reflectance spectra using the transfer matrix method [7, 16, 21], and oscillated between 68.5% and 78.3%. A thickness of 3,530 nm and pore sizes ranging from 25 to 45 nm in diameter were determined using scanning electron microscopy (data not shown).