Yq. Zhao et Mw. Urban, Effect of hydrophobic tails on orientation of SDS and SDOSS surfactants near the film-air interface of Sty/n-BA copolymer latex films, LANGMUIR, 17(22), 2001, pp. 6961-6967
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.