Stopband attenuation of silica spheres by attaching aniline and polyaniline

To control the stopband, the surface of the silica spheres (SS) has been modified with aniline (SSAn) which has been polymerized (SSPAn) with an ammonium persulfate. N-[3-(trimethoxysilyl)propyl]aniline (TMSPA) was attached on the surface of the silica spheres via hydrolysis and condensation reactions with base catalyst. Fourier transform infrared (FTIR) spectrum of the SSAn shows the new peaks at 1372, 1508, 1561 and 1692 cm−1 corresponding CN stretching vibration, CC stretching vibration of benzene ring, NH bending vibration and possibly NHN stretching vibration and also shows absorption peak shift from 3225 to 3450 cm−1 representing the change of main absorption from free OH to NH. After polymerization of the aniline moiety, the OH and NH absorption peaks drastically reduced and new sharp peaks appeared at 1398 and 617 cm−1 representing CN and CS stretching vibrations, respectively. These FTIR results provide the evidence of the existence of aniline and polyaniline on the surface of the silica spheres. The stopbands of the SS, SSAn and SSPAn are at 831, 875 and 848 nm, respectively. The stopband of SSAn shifted 44 nm toward red compared with that of SS. This large stopband change is due to the large refractive index difference between SiO2 (1.46) and aniline (1.586). The stopband of SSPAn shifts toward blue compared with SSAn, which may be due to the refractive index reduction of polyaniline (1.2–1.8) compared with aniline.