Surface properties of new catanionic semi-fluorinated hybrid surfactants Alioune Diouf a,b , Elisabeth Taffin de Givenchy a , Samba Yande ´ Dieng b , Abdoulaye Drame ´ a,b , Sonia Amigoni a , Thierry Darmanin a , Fre ´ de ´ ric Guittard a, * a Univ. Nice Sophia Antipolis, CNRS, LPMC, UMR 7336, 06100 Nice, France b De ´partement de Chimie, Faculte ´ des Sciences et Techniques, Universite ´ Cheikh Anta Diop, Dakar, Senegal 1. Introduction A lot of research efforts are devoted to the progress in the molecular design of new surfactant molecules, in particular for medical or health care applications [1–4]. Specifically, the ability of these surfactant systems to self assemble was particularly studied for the development of drug delivery systems [5,6], templating applications [7] or nanoreactors [8]. Inventive systems like multi compartment micelles formed by polymeric surfactants [9,10] or by catanionic associations [11–13] have been developed. Indeed, catanionic surfactants are made up of stoichiometric amounts of cationic and anionic surfactants, where the inorganic counterions have been removed, leaving two amphiphilic ions oppositely charged [14]. This modification of electrostatics leads to physico- chemical properties and aqueous aggregation distinct from cationic/anionic surfactant mixtures [15]. Catanionics behave as double chained amphiphiles [16]. Among them, hydrocarbon/fluorocarbon hybrid surfactants are strong associative surfactants and their mutual phobicity induces the creation of non conventional interactions and aggregates. Very stable vesicles could be observed along with some peculiar intermediate structures such as threadlike micelles transforming into bilayers or vesicles [17] nanocage aggregates [18] polyhedral vesicles [19,20] or multi compartiment micelles [21]. In this work we wanted to study the aggregation behaviour of new catanionic hybrid surfactants. In this aim, we have designed the surfactants noted F n QN m , shown in Fig. 1, which possess in the same structure a polar quaternary ammonium head and two hydrophobic chains: a semifluorinated tail and hydrocarbon one. These hybrid structures are known to combine [22–24] the so particular surface properties generally induced both by the fluorinated tail and the gemini structure (two tailed surfactants) [25] without facing the low water solubility often encountered for highly fluorinated compounds. Furthermore, hybrid fluorocarbon/ hydrocarbon structures allow the surfactants to emulsify either fluorinated or hydrocarbon fluids [26] and to be used in a large scale of applications [27] (Scheme 1). 2. Results and discussion 2.1. Synthesis The new hybrid surfactants we describe in this paper are readily achieved in three or four steps from semi-fluorinated thiol Journal of Fluorine Chemistry 161 (2014) 60–65 ARTICLE INFO Article history: Received 16 December 2013 Received in revised form 5 February 2014 Accepted 8 February 2014 Available online 16 February 2014 Keywords: Semi-fluorinated surfactants Catanionic surfactants Hybrid surfactants Vesicles ABSTRACT In order to study their aggregation behaviour, a rapid synthetic procedure from perfluoroalkylethyl thiol derivatives led to twenty four original catanionic hybrid surfactants of general formula: [R F (CH 2 ) 2 S(CHQ) 2 CO 2  ; HN + (CH 3 ) 2 R H (Q = H or Cl; R F =C 4 F 9 ,C 6 F 13 ,C 8 F 17 ;R H =C 6 H 13 ,C 8 H 17 ,C 10 H 21 , C 12 H 25 )]. Critical aggregation concentration (CAC), surface tension at the CAC (g S ) and free energy of aggregation ðDG A  Þ of the title surfactants, in aqueous solution, have been investigated as a function of the number of carbon atoms in both the fluorinated and the hydrocarbon tails. TEM studies were used to estimate the shape and size of the aggregates and confirmed the general tendency of fluorinated surfactants to form aggregates with lesser curvature. These catanionic surfactants exhibited very low surface tension at critical aggregation concentration (CAC) of 15.3–17.4 mN m 1 as well as low CAC of 3  10 5 –11  10 3 and the substitution of one hydrogen atom by one chlorine atom didn’t affect significantly the aggregation phenomenon. ß 2014 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +33 04 92 07 61 59; fax: +33 04 92 07 61 56. E-mail address: Frederic.Guittard@unice.fr (F. Guittard). Contents lists available at ScienceDirect Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor http://dx.doi.org/10.1016/j.jfluchem.2014.02.004 0022-1139/ß 2014 Elsevier B.V. All rights reserved.