The phase equilibria of aqueous solutions of n-alkyl polyoxyethylene ethers (CiEj) are characterized by the presence of so-called cloud curves which represent the region of liquid−liquid immiscibility of two micellar solutions (one rich and one poor in surfactant). The systems exhibit a lower critical solution temperature (LCST), which denotes the lower limit of immiscibility; in some cases a complete closed-loop region with an upper critical solution temperature (UCST) is seen corresponding to re-entrant miscibility. In this case the behavior can be explained in terms of the competition between the incompatibility of water with the alkyl chain and the hydrogen bonding between water and the head groups. We have used a simplified version of the statistical associating fluid theory (SAFT), which is based on the thermodynamic perturbation theory of Wertheim for associating fluids:  the original SAFT-LJ equation of state treats the molecules as chains of Lennard-Jones segments while the simplified SAFT-HS equ...

An Examination of the Cloud Curves of Liquid−Liquid Immiscibility in Aqueous Solutions of Alkyl Polyoxyethylene Surfactants Using the SAFT-HS Approach with Transferable Parameters

Thirty years of research and the use of EoS/GE mixing rules in cubic equations of state are reviewed. The most popular approaches are presented both from the derivation and application points of view and they are compared to each other. It is shown that all methods have significant capabilities but also limitations which are discussed. A useful approach is presented for analyzing the models by looking at the activity coefficient expression derived from the equations of state using various mixing rules. The size-asymmetric systems are investigated in detail, and an explanation is provided on how EoS/GE mixing rules should be developed so that such asymmetric mixtures are adequately represented.

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Thirty Years with EoS/GE Models - What Have We Learned?

The phase equilibria of water + n-butan-1-ol is characterized by the presence of so-called closed-loop curves which represent regions of liquid-liquid immiscibility in the phase diagram. The system...

Predicting the high-pressure phase equilibria of binary aqueous solutions of 1-butanol, n-butoxyethanol and n-decylpentaoxyethylene ether (C10E5) using the SAFT-HS approach

E.H. Stenby

Papers

Modelling the influence of pressure on the phase behavior of systems containing water oil and nonionic surfactants