Liquid Phase Behavior of Perfluoroalkylalkane Surfactants

Abstract

We have performed a combined experimental and theoretical study of the thermodynamic properties of semifluorinated alkanes. In particular, the liquid density of perfluorohexylhexane (F6H6) and perfluorohexyloctane (F6H8) has been measured as a function of temperature from 273.15 to 353.15 K and at four temperatures as a function of pressure up to 600 bar. The results were interpreted using the SAFT-VR equation of state. The perfluoroalkylalkanes were modeled as heterosegmented diblock chains using parameters for the alkyl and perfluoroalkyl segments developed in earlier work. Through this simple approach, we are able to predict the thermodynamic behavior of the perfluoroalkylalkanes studied without fitting to any experimental data for the systems being studied.

Vapor-liquid critical and interfacial properties of square-well fluids in slit pores

“…SW model was introduced originally to understand simple liquid; 34 however, due to its analytic tractability it has become even more useful for colloidal system, [35][36][37] heterochain molecules, [38][39][40] and complex system, [41][42][43] among others.…”

Theoretical investigation of the phase behaviour of model ternary mixtures containingn-alkanes, perfluoro-n-alkanes, and perfluoroalkylalkane diblock surfactants

“…The SAFT approach has been extended to deal with different intermolecular potentials, such as the SAFT-VR extension developed by Gil Villegas et al [32,33] that describes the behaviour of chains formed by spherical segment interacting through a potential of variable range, typically the square-well potential. The SAFT-VR approach, as other versions of SAFT, can be considered as one of the most powerful predicting equations of state nowadays for determining the thermodynamic properties of systems as complex as chain-like, including the n-alkane series, the perfluoro-n-alkanes and their mixtures [33][34][35][36][37][38], systems with refrigerants [39][40][41], surfactants [42][43][44][45][46], polymeric [47][48][49][50] and aqueous systems [51][52][53], among others. In recent works [43][44][45][46], in a collaboration with other research groups, we have used a modification of the SAFT-VR approach, called hetero-SAFT-VR [54][55][56], where molecules are composed of different segments, to predict some thermodynamic properties, including the phase equilibrium of two different perfluoroalkylalkane molecules, namely the perfluorohexylhexane and perfluorohexyloctane, without the need of experimental data from these surfactants.…”

“…The same can be done for the unlike interactions between both chemical groups. Using an appropriate rule for the number of chemical units in the surfactant molecule, the resulting equation of state is able to predict successfully the saturated liquid density and vapour pressure of several pure perfluoroalkylalkanes without any further fitting [44]. During last three years, several authors have combined the group contribution approaches with the SAFT approach in order to better account for the effects of molecular structure and composition.…”

“…The main goal of this work is to investigate and provide a general picture of the phase behaviour of these mixtures. To this end, we use different sets of reasonable molecular parameters presented previously [43][44][45][46] to describe the chemical units of n-alkanes, perfluoroalkanes and perfluoroalkylalkanes. It is important to recall that our objective is not to provide a detailed quantitative description of the phase behaviour of these mixtures, but to give an insight of the general features exhibited by these mixtures.…”

“…The SFAs or perfluoroalkylalkanes surfactants, F i H j , are formed by linear alkane chains bonded to linear perfluoroalkane chains, which can be regarded as semi-flexible copolymers. Following a similar approach used in earlier works [43][44][45][46], the diblock surfactant molecules are modelled using a heteronuclear model that considers two homonuclear chains for each branch of the surfactant bonded together. The alkyl branch is also modelled by an united atom approach, where m A hard-sphere attractive segments of equal diameter σ AA , which are tangentially bonded to form the chain.…”