Multivalent counterion induced multilayer adsorption at the air-water interface in dilute Aerosol-OT solutions

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:597

Article

Wang, Zi^1,2  Li, Peixun²  Ma, Kun²  Chen, Yao²  Webster, John R. P.²  Campana, Mario²  Yan, Zifeng¹  Penfold, Jeff^2,3  Thomas, Robert K.³ 

[1] China Univ Petr, Sch Sci, State Key Lab Heavy Oil Proc, Qingdao 266580, Peoples R China

[2] STFC, Rutherford Appleton Lab, ISIS Facil, Didcot OX11 0QX, Oxon, England

[3] Univ Oxford, Phys & Theoret Chem Lab, South Pk Rd, Oxford OX1 3QZ, England

关键词: Surface multilayer formation;    Multivalent counterions;    Aerosol-OT;    Air-water interface;    Anionic surfactants;   

DOI  :  10.1016/j.jcis.2021.03.183

来源: Elsevier

【 摘 要 】

The formation of surface multilayer structures, induced by the addition of multivalent counterions in dilute surfactant solutions, has been widely observed in a range of anionic surfactants. The phenomenon is associated with the ability to manipulate surface properties, especially in the promotion of enhanced surface wetting, and in the presence of an extensive near surface reservoir for rapid surface delivery of surfactant and other active components. Hypothesis. In the single alkyl chain anionic surfactants, such as sodium dodecysulfate, SDS, sodium alkylethoxylsulfate, SAES, and alkylestersulfonate, AES, surface multilayer formation is promoted by trivalent counterions such as Al3+, and is generally not observed with divalent counterions, such as Ca2+ or with monovalent counterions. In the di-alkyl chain anionic surfactant, dodecylbenzenesulfonate, LAS, surface multilayer formation now occurs in the presence of divalent counterions. It is attributed to the closer proximity of a bulk lamellar phase, resulting in a greater tendency for surface multilayer formation, and hence should occur in other di-alkyl chain anionic surfactants. Experiments. Aerosol-OT, AOT, is one of the most commonly used di-alkyl chain anionic surfactants, and is exten-sively used as an emulsifying, wetting and dispersing agent. This paper reports on predominantly neutron reflectivity, NR, measurements which explore the nature of surface multilayer formation of the sodium salt of AOT at the air-solution interface with the separate addition of Ca2+ and Al3+ counterions. Findings. In the AOT concentration range 0.5 to 2.0 mM surface multilayer formation occurs at the air-solution interface with the addition of Ca2+ or Al3+ counterions. Although the evolution in the surface structure with surfactant and counterion concentration is broadly similar to those reported for SDS, SAES and AES, some notable differences occur. In particular the surfactant and counterion concentration thresholds for surface multilayer formation are higher for Ca2+ than for Al3+. The differences encountered reflect the greater affinity of the di-alkyl chain structure for lamellar formation, and how the surface packing is con-trolled in part by the headgroup structure and the associated counterion binding affinity. (C) 2021 Elsevier Inc. All rights reserved.

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