Molecular Interactions of a Polyaromatic Surfactant C5Pe in Aqueous Solutions Studied by a Surface Forces Apparatus

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• 作者：Jing Wang ; Qingye Lu ; David Harbottle ; Johan Sj枚blom ; Zhenghe Xu ; Hongbo Zeng
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：September 13, 2012
• 年：2012
• 卷：116
• 期：36
• 页码：11187-11196
• 全文大小：632K
• 年卷期：v.116,no.36(September 13, 2012)
• ISSN：1520-5207

文摘

Studies on molecular mechanisms of polyaromatic surfactants in stabilizing water-in-oil (W/O) or oil-in-water (O/W) emulsions are of great scientific and practical importance. A polyaromatic surfactant N-(1-hexylheptyl)-N鈥?(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe) with well-defined molecular structure containing fused aromatic rings and heteroatoms similar to asphaltene molecules, was used in this study in an attempt to understand molecular interaction mechanisms of heavy oil components in aqueous solutions. A surface forces apparatus (SFA) was used to directly measure the molecular interactions of C5Pe. Solution pH, salt concentration and Ca²⁺ addition showed a strong impact on molecular interactions between C5Pe adsorbed on mica surfaces. The repulsion observed between the two adsorbed C5Pe molecular layers was shown to have a steric and electrosteric origin. The force鈥揹istance profiles at short separation distances under high compression force were well fitted with the Alexander-de Gennes (AdG) model. At pH 鈮?4, the repulsive forces measured over a long separation distance under low compression force were shown to deviate from the AdG model but could be fitted with the Derjaguin鈥揕andau鈥揤erwey鈥揙verbeek (DLVO) theory, indicating an electrostatic origin of the observed repulsion due to ionization of 鈭扖OOH groups. Adhesion between two C5Pe surfaces was shown to decrease sharply with increasing solution pH and salt concentration, being attributed to the decrease in surface hydrophobicity and hence hydrophobic attraction. Addition of Ca²⁺ ions induced the formation of large C5Pe aggregates due to strong bonding of Ca²⁺ with 鈭扖OOH groups, leading to a longer range steric repulsion. Our results provide a new insight into the molecular interactions of polyaromatic surfactants at oil鈥搘ater interfaces and in complex aqueous solutions.