Effect of Hydrophobic Tails on Orientation of SDS and SDOSS Surfactants Near the Film-Air Interface of Sty/n-BA Copolymer Latex Films

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Polymers and High Performance Materials


This study focuses on the effect of sodium dioctylsulfosuccinate (SDOSS) and sodium dodecyl sulfate (SDS) surfactants on mobility and conformational behavior in styrene/n-butyl acrylate/methacrylic acid (Sty/n-BA/MAA) copolymer latex films. Because of similar hydrophilicity of SO3-Na+ groups but differences in hydrophobic tails, SDOSS and SDS are examined near the surface for coalesced Sty/n-BA/MAA latex films. These studies show that the presence of hydrophilic SO3-Na+ groups and hydrophobic entities represented by two C8H17 tails in SDOSS and one C12H25 hydrophobic group in SDS significantly affects the magnitude of surfactant-latex matrix interactions. Furthermore, not only the surfactant conformational behavior near the film-air interface is affected but also the magnitude of the interactions of hydrophilic SO3-Na+ groups in SDOSS with H2O and COOH groups of Sty/n-BA/MAA is substantially different from its SDS counterpart. This is demonstrated by the splitting of the S-O band when hydrophilic SDOSS groups interact with H2O and COOH groups of the polymer matrix. Attenuated total reflectance Fourier transform infrared polarization studies and energy calculations using a semiempirical quantum-mechanical approach indicate that hydrophobic chains take preferentially perpendicular orientations to the latex film surface, whereas hydrophilic, SO3-Na+ groups are preferentially parallel. Semiquantitative dichroic ratio analysis revealed that the degree of orientation of the SO3-Na+ groups is also affected by hydrophobic entities.

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