Surface and interfacial fourier transform infrared spectroscopic studies of latexes. XVI. Quantitative analysis of surfactant in multilayered films

Migration and concentration levels of sodium dioctylsulfosuccinate (SDOSS) surfactant molecules in 50%/50% styrene/butyl acrylate latex were detected at the film-substrate (F-S) and film-air (F-A) interfaces in mono- and double-layered films. For the purpose of quantitative analysis, absorption coefficients of the 1,056 and 1,046 cm⁻¹ bands attributed to the SO₃⁻Na⁺…HOOC and SO⁻₃Na⁺…H₂O associations, respectively, were determined. Using group theory formalism, local geometries of the SO⁻₃Na⁺ hydrophilic groups of SDOSS can be predicted. The analysis is extended to the 1,261 and 1,209 cm⁻¹ bands resulting from the S—O asymmetric stretching vibrations, due to the same SO⁻₃Na⁺ … HOOC and SO⁻₃Na⁺ … H₂O associations, and to the 1,290 and 1,236 cm⁻¹ bands, due to asymmetric stretching modes of hydrophobic tails of the SDOSS. By the use of polarization attenuated total reflectance Fourier transform infrared (ATRFT-IR) experiments, these studies show that hydrophilic SO⁻₃Na⁺ ends on SDOSS are preferentially parallel to the film surface. At the same time, hydrophobic tails are perpendicular to the surface. The assessment of the amounts of SDOSS at the F-S and F-A interfaces was obtained by quantitative ATR FTIR analysis, which was extended to the silicone-modified double-layer latex films. In this case, the concentration of SDOSS molecules decreases as the depth of penetration increases. The highest concentrations of SDOSS molecules are detected at the shallowest depths near the surface of the top layer and the interfacial regions between the latex layers. © 1996 John Wiley & Sons, Inc.