Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces

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• 作者：Kamil Wojciechowski ; ^{kamil.wojciechowski@ch.pw.edu.pl}
• 关键词：Saponins ; Adsorption ; Ionic surfactants ; Air&ndash ; water ; Olive oilwater ; Tetradecane&ndash ; water
• 刊名：Colloids and Surfaces B: Biointerfaces
• 出版年：2013
• 出版时间：1 August, 2013
• 年：2013
• 卷：108
• 期：Complete
• 页码：95-102
• 全文大小：796 K

文摘

Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated ¡°Sigma¡± QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. (¡°Supersap¡±), employed in a recent study by Stanimirova et al. . The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37 nm² vs. 1.19 nm² for ¡°Sigma¡± and ¡°Supersap¡±, respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for ¡°Sigma¡± the surface storage modulus, ¦Å_r = 103 mN m^?1, while for ¡°Supersap¡± ¦Å_r = 73 mN m^?1 at 10^?3 mol l^?1 (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the ¡°Supersap¡± from Desert King is a non-ionic one.