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Hydrophobic additives, such as essential oils or fragrances, can have a tremendous impact on the viscosity and viscoelasticity of aqueous surfactant gels. The effects are best understood by constructing complete salt curves using sodium laureth sulfate (SLES) in the presence of various additives. A total of four distinct mechanisms of solute-surfactant interactions was identified that differently affect the position and amplitude of the salt curve, resulting in shifts to the left or to the right, or an increase or decrease in viscosity, respectively [1,2]. The effects are intimately linked to the location of the additives within the surfactant film, which is governed by the molecular characteristics of the additives, such as polarity and amphiphilicity.
Mathematical expressions have been established to incorporate each of the four mechanisms into a previously developed analytical model to calculate surfactant salt curves based on differences in packing parameter and chemical potential of three distinct microphases, endcaps, cylinders and junctions [2,3].
References :
[1] A. Parker, W. Fieber. Soft Matter 9 (2013), 1203.
[2] W. Fieber, A. Scheklaukov, W. Kunz, M. Pleines, D. Benczédi, T. Zemb. J. Mol. Liq. 329 (2021), 115523.
[3] M. Pleines, W. Kunz, T. Zemb, D. Benczédi, W. Fieber. J. Colloid Interface Sci. 537 (2019), 682.
