Interfacial Interaction between Cellulose Derivatives and Surfactants at Solid Surfaces. An Ellipsometry Study

The effect of surfactants on the adsorption properties of ethyl(hydroxyethyl)cellulose (EHEC) and its hydrophobically modified analogue (HM-EHEC) at the solid−liquid interface has been studied by ellipsometry. The adsorption characteristics of EHEC and HM-EHEC without the presence of surfactants are also presented. The polar silica surface and a hydrophobized silica surface were used as substrates. On the polar silica surface, a small addition of the anionic surfactant sodium dodecyl sulfate (SDS) caused a 3- to 5-fold expansion of the preadsorbed EHEC or HM-EHEC layers, while the adsorbed amount was less influenced. On the hydrophobized silica surface, SDS could replace EHEC (>10 mM SDS), while some adsorbed HM-EHEC still could be detected well above the critical micelle concentration of SDS in the bulk (14 mM). The nonionic surfactant octa(ethylene oxide) dodecyl ether (C 12 E 8 ) did not affect the adsorbed layer structure on silica, and the cationic surfactant cetyltriammonium chloride (CTAC) on hydrophobized silica showed similar effects as SDS but with a smaller magnitude. It is proposed that the adsorbed layer structure mainly is governed by polymer−surfactant interfacial interactions.