Abstract
The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (CnEOm) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C14EO4 and C14EO8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of CnEOm adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C14EO4, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C14EO8, a number of s = 10 adsorption states allows an optimum data description.
Highlights
Surfactants are applied almost everywhere in our life
Lee at al. showed, by molecular dynamics simulations on poly glycols (PEG) and oxides (PEO), that the persistence length of the EO chain is about 0.37 nm, confirming the extreme flexibility of this chain [21]; we studied this phenomenon experimentally in [22]
The assumption that surfactant molecules can adsorb at the interface in two possible states assumption that surfactant molecules can adsorb at the interface in two possible states was superior over the Langmuir and Frumkin model in particular for surfactants with a was superior over the Langmuir and Frumkin model in particular for surfactants with a rather larger head group
Summary
Surfactants are applied almost everywhere in our life. Many technologies are even based on the action of surface-active molecules. Surfactants are generally well studied, and the properties of their adsorption layers are quantitatively determined (see, for example, [1,2,3]). The analysis of available experimental data (such as dynamic and equilibrium surface tensions, adsorption, and limiting dilational viscoelasticity) is made on the basis of the classical adsorption models of Langmuir [4] or Frumkin [5]. These most frequently applied models do not always provide a satisfactory description of the measured results
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