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The present study is concerned with the determination of the critical micelle concentration (cmc) of mixed micelles of sodium dodecyl sulfate with one of five nonionic surfactants (Triton X-100, Tween 20, Tween 60, Tween 80 or Tween 85) from conductance measurements. Based on the calculated values of the β parameters we have noticed that SDS-nonionic surfactants mostly showed strong synergistic effect. It was found that nonionic surfactants with mainly longer and more hydrophobic tail show stronger interactions with hydrophobic part of SDS, thus expressing stronger synergism. In SDS-Tween 80 binary system the strongest synergistic effect was noticed. SDS-Tween 85 micellar system showed antagonistic effect, most probably because the presence of the double bond in its three hydrophobic tails (three C18 tails) makes it sterically rigid.

Abstract Polymer - surfactant aqueous systems are important for a variety of industrial applications. The properties of those systems among other depend on the interactions between them. The aim of this work was to determine interactions between anionic polymer - xanthan gum and anionic surfactant - SDS or nonionic surfactant - Tween 80. In order to get better insight into the occurrence and possible mechanism of interactions several techniques were used such as FTIR, viscometry, conductometry, tensiometry, fluorimetry as well as SEM analysis. The results obtained by the combination of all those techniques showed that xanthan gum – SDS/Tween 80 interactions existed. Structural changes of xanthan gum molecules in presence of both surfactants were obtained by viscometry and SEM. The characteristic interaction points (CAC and PSP) were determined by measuring surface tension and specific conductance of pure surfactant aqueous solutions and their mixtures with xanthan gum. The values of PSP were proportional to the polymer concentration. After overcoming electrostatic repulsion between xanthan gum and SDS, they form complexes through hydrophobic mechanism and enhance adsorption of SDS molecules at the water – air interface. Unlike SDS, Tween 80 mainly interacts with xanthan gum in the bulk creating hydrogen bonds as well as by hydrophobic interactions. The results of fluorescence measurements expressed as I 1 /I 3 ratio additionally confirmed that the mechanism of interactions between xanthan gum and examined surfactants was mainly through hydrophobic interaction and by creation the hydrogen bonds with Tween 80 as through electrostatic repulsion with SDS. Graphical abstract Image 1 Highlights • Occurrence and mechanism of interactions in the xanthan gum –SDS/Tween 80 system. • Interactions between xanthan gum and SDS occurred through electrostatic repulsion and hydrophobic mechanism. • Xanthan gum-Tween 80 complexes are formed dominantly through hydrophobic interaction and hydrogen bonds. [ABSTRACT FROM AUTHOR]

Mixtures of a cross-linked polyacrylic acid (Carbopol 940) and two types of surfactants, namely anionic sodium dodecylsulfate (SDS) and nonionic Tween 80, were investigated by viscometry, conductometry, tensiometry, spectrophotometry, fluorimetry and scanning electron microscopy (SEM). The addition of nonionic surfactant decreased the reduced viscosity and the transmittance of the Carbopol polymer aqueous solutions. Furthermore, the interaction between Carbopol 940 and SDS was characterized by two significant concentration values: the critical aggregation concentration of SDS was particularly independent of Carbopol polymer concentration while the polymer saturation point of both surfactants increased with the increase in polymer content. The values of critical aggregation concentration and polymer saturation point obtained using various techniques confirmed the occurrence of Carbopol polymer-surfactant associations. The effect of different SDS and Tween 80 concentrations on the conformation of Carbopol 940 in aqueous solution could be explained through hydrophobic association between surfactant micelles and Carbopol polymer tails and through hydrogen bonding in the case of Tween 80. Additionally, the surfactant-induced structural changes were confirmed in Carbopol 940-SDS and Carbopol 940-Tween 80 aqueous solutions by SEM measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Xanthan gum-Carbopol 940 complexes are formed when two polymers are mixed together. • Hydrophobic and electrostatic interactions occurred in ternary mixtures with SDS. • Hydrophobic and hydrophilic interactions occurred in ternary mixtures with Tween 80. The development and optimization of systems consist of polymers and surfactants are strongly related to the presence of interactions between them. Therefore, the interpolymer complexes between biopolymer xanthan gum and synthetic polymer Carbopol 940 were investigated before and after the addition of surfactant. The mechanism of interactions in ternary system consisted of xanthan gum, Carbopol 940 and anionic surfactant (sodium dodecylsulfate) as well as nonionic surfactant (Tween 80) was studied by the combination of different techniques such as viscometry, conductometry, tensiometry, spectrophotometry and fluorimetry. Xanthan gum and Carbopol 940 formed complexes through hydrogen bonding and hydrophobic interactions. Therefore, the calculated specific viscosities of polymer blends were much lower than experimentally determined values. Namely, both polymers participated in the association process with sodium dodecylsulfate or Tween 80. In case of anionic surfactant hydrophobic interactions between sodium dodecylsulfate and xanthan gum-Carbopol 940 complexes exist together with electrostatic repulsive forces between the same charged groups. Tween 80 interacts with xanthan gum-Carbopol 940 complexes through hydrogen bonds and hydrophobic interactions. The formed xanthan gum-Carbopol 940 complexes with sodium dodecylsulfate or Tween80 could find their application by optimizing the interactions in the system of xanthan gum and Carbopol 940 using the appropriate concentration of surfactant. [ABSTRACT FROM AUTHOR]