Quantitative ATR FT-IR analysis of surface segregation of polymer blends of polystyrene/poly(dimethylsiloxane)-co-polystyrene

The surface segregation of a series of two-component polymer blends of polystyrene/poly(dimethylsiloxane)-co-polystyrene has been studied by attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. We examined the details of calibration for quantitative ATR FT-IR. The quantitation is based on calibration of Beer's law by transmission FT-IR measurements. The effect of spectral distortion and penetration depth dependence of radiation wavelength due to ATR sampling is evaluated. ATR spectra are corrected for penetration depth dependence before being used for quantitation. The corrected ATR spectra were compared with the transmission spectra of the same samples. Peak area ratios using one peak from each component were measured for the determination of the concentration of surface poly(dimethylsiloxane). The correction and calibration procedure improves the accuracy of quantitative surface analysis in the range of micrometer sampling depth. Unlike other approaches for quantification of ATR data on polymers, this method can be used for systems with a complex, unknown concentration gradient near the surface such as the blend system reported here.