Modification of Chrysotile Surface by Organosilanes: An IR-Photoacoustic Spectroscopy Study

Chrysotile and its dimethylsilyl (DMS) and dimethylphenylsilyl (DMPS) derivatives were studied by Fourier transform infrared–photoacoustic spectroscopy. In the Si–O stretching region of chrysotile a new band was revealed at 985 cm−1, besides absorptions at 1083, 1028, and 947 cm−1. The Si–O stretching frequencies did not undergo major changes in the DMS derivative, but the 985- and 1028-cm−1 peaks were undetected in DMPS due to the HCl attack on chrysotile tetrahedral sheets. Similar effects were observed in the region 900–400 cm−1, by a decrease in intensities of the 600- and 642-cm−1 Mg-OH libration modes in the DMPS spectrum, indicating also a HCl attack on the octahedral sheet. The Si–C band at 800 cm−1 in the spectra of both DMS and DMPS was accompanied by minor components. DMPS showed a strong peak at 813 cm−1 assigned to a Si–phenyl vibration. A sharp peak at 1263 cm−1 in the DMS spectrum was ascribed to a diagnostic C–H bending mode of the dimethylsilyl groups in DMS. The complex bands around 1413 cm−1 in DMS were attributed to CH3 deformation vibrations and that at 1466 cm−1 in DMPS to phenyl groups. In DMPS a distinct peak at 1593 cm−1 was attributed to a Si–phenyl vibration. In the region 3700–2500 cm−1 absorptions at 2964, 2931, and 2907 cm−1 in DMS were ascribed to C–H-stretching vibrations of dimethylsilyl groups, while a strong peak at 2919 cm−1 in the DMPS spectrum was attributed to a Si–C6H5 mode.