Structures of adsorption layers of surfactant mixtures on nonpolar solid surfaces
The structure of the adsorbed layer of mixtures of a low molecular mass nonionic surfactant (alkyl heptaglycolether, C12EO7) with low molecular mass anionic (sodium dodecylsulfate, SDS, and sodium dodecylbenzenesulfonate, SDBS) and high molecular mass nonionic surfactants (EO37PO56EO37) was studied by atomic force microscopy in the combination with adsorption isotherms and adsorption enthalpies by isothermal titration calorimetry. The single surfactants C12EO7 and SDS show domains of parallel stripes on the graphite lattice in the atomic force microscopy (AFM) images. These parallel stripes can be related to hemicylindrical aggregates of a width of about 5 nm repeated in a periodic order which was proposed by different authors before. These structures are backed up by the results of the adsorption isotherms and the calorimetric measurements of the adsorption enthalpies. For SDBS and the high molecular mass nonionic surfactant, no such structures are observed in the AFM images despite an adsorption of surfactants on the surface. Mixtures of C12EO7 and the anionic surfactants give similar parallel stripes as the nonionic surfactant alone even in combination with SDBS, which indicates ideal mixing behavior on the surface. The concentration ratio of the surfactants on the surface differs from that in solution. For a mixed system of C12EO7 and the high molecular mass nonionic surfactant, a demixing of the surfactants on the surface can be assumed.
KeywordsAtomic force microscopy Surfactant Aggregation Adsorption
The authors would like especially to thank Prof. Dr. H. Hoffmann for many interesting and valuable discussions about phase behavior and micellization for this work and throughout many years in research.
- 3.Tadros TF (1987) Solid liquid dispersions. Academic Press, LondonGoogle Scholar
- 4.Dobiás B, Qiu X, von Rybinski W (1999) Solid–liquid dispersions. Marcel Dekker, New YorkGoogle Scholar
- 19.Flemming BD, Wanless EJ (2000) Soft-contact atomic force microscopy imaging of adsorbed surfactant and polymer layers. Microsc Microanal 6:104–112Google Scholar
- 21.Jabnoun M (2012) Adsorption layers of surfactant mixtures on non-polar solid particles and stability of dispersions, PhD thesis. University of Duesseldorf, GermanyGoogle Scholar
- 22.van Megen J (2013) Aggregation structures of mixtures of high and low molecular mass surface active substances on surfaces and in the bulk phase, Master thesis. University of Duesseldorf, GermanyGoogle Scholar
- 26.Kaplik H (2012) Surface activity and aggregation in solutions of mixtures of anionic and nonionic surfactants, Bachelor thesis. University of Duesseldorf, GermanyGoogle Scholar
- 36.Chobanu MM, Ropot VM (1981) Zh. Prikl. Khim. 54:2221 in Schick MJ (1987) Nonionic surfactants. Marcel Dekker, New York, p 106Google Scholar
- 37.Gao Y, Zhang Y, Huang Z, Gu T (1989) Acta Sci Nat Univ Pekin 25:726–733Google Scholar
- 39.Couderc S, Li Y, Bloor DM, Holzwarth JF, Wyn-Jones E (2001) Interaction between the nonionic surfactant hexaethylene glycol mono-n-dodecyl ether (C12EO6) and the surface active nonionic ABA block copolymer pluronic F127 (EO97PO69EO97)-formation of mixed micelles studied using isothermal titration calorimetry and differential scanning calorimetry. Langmuir 17:4818–4824CrossRefGoogle Scholar