Effect of hydrophobic tails on orientation of SDS and SDOSS surfactants near the film-air interface of Sty/n-BA copolymer latex films

This study focuses on the effect of sodium dioctylsulfosuccinate (SDOSS) an d sodium dodecyl sulfate (SDS) surfactants on mobility and conformational b ehavior in styrene/n-butyl acrylate/methacrylic acid (Sty/n-BA/MAA) copolym er latex films. Because of similar hydrophilicity of SO3-Na+ groups but dif ferences in hydrophobic tails, SDOSS and SDS are examined near the surface for coalesced Sty/n-BA/MAA latex films. These studies show that the presenc e 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 interfa ce is affected but also the magnitude of the interactions of hydrophilic SO 3-Na+ groups in SDOSS with H2O and COOH groups of Sty/n-BA/MAA is substanti ally different from its SDS counterpart. This is demonstrated by the splitt ing of the S-O band when hydrophilic SDOSS groups interact with H2O and COO H groups of the polymer matrix. Attenuated total reflectance Fourier transf orm infrared polarization studies and energy calculations using a semiempir ical quantum-mechanical approach indicate that hydrophobic chains take pref erentially perpendicular orientations to the latex film surface, whereas hy drophilic, SO3-Na+ groups are preferentially parallel. Semiquantitative dic hroic ratio analysis revealed that the degree of orientation of the SO3-Na groups is also affected by hydrophobic entities.