Self-Assembly of Polyoxovanadate-Containing Fluorosurfactants Baofang Zhang, † Jie Song, ‡ Dong Li, † Lang Hu, † Craig L. Hill,* ,‡ and Tianbo Liu* ,† † Department of Polymer Science, The University of Akron, Akron, Ohio 44325, United States ‡ Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States * S Supporting Information ABSTRACT: Two novel polyoxovanadate (POV)-containing fluorosur- factants, each with two hydrophobic fluorinated “tails” and one nanosized, hydrophilic, rigid POV “head group”, are synthesized for the first time. They self-assemble into spherical, bilayer vesicles in acetonitrile/water mixed solvents, as evidenced by systemic studies using laser light scattering (LLS) and electron microscopy techniques. The vesicle sizes demonstrate dynamic change over different solvent compositions mainly as a result of the solvent swelling of the fluorocarbon chains, although the charge number on the POVs changes over the solvent polarity as well. ■ INTRODUCTION Fluorosurfactants are fluorinated chemical compounds that typically consist of a fluorinated hydrophobic “tail” and a hydrophilic “head group”. 1 Fluorine atoms in the structure offer distinct properties from the corresponding hydrogenated counterpart. For instance, fluorosurfactants are not only chemically and thermally more stable but also more effective at lowering the surface tension of solutions; i.e., they are stronger surfactants than the surfactants based on hydrocarbon chains. 2-4 The special properties of these materials have attracted considerable attention in many research fields. 5,6 Recently, more sophisticated structures, such as nanotubular microstructures 7,8 and mixed Langmuir monolayers, 9 assembled from fluorinated compounds are reported. Their unique structures show great potential in multiple biomedical applications. For example, the fluorinated polymers have been extensively investigated as possible blood substitutes, 10 as a result of their superb oxygen transport property. Polyoxometalates (POMs) are a large group of metal oxide molecular nanoclusters with a broad range of applications in catalysis, medicine, and material science. 11-17 These hydro- philic compounds have well-defined size, shape, charge, and other structural features, and they exhibit the capability of reversible and stepwise multi-electron transfer or storage without significant structural change. Recently, these inorganic clusters have been successfully covalently grafted with organic components through various synthetic methods, forming novel amphiphiles of various structures. 18-22 For example, inorganic- organic hybrids containing a single POM component have been synthesized with one 23,24 or two 25 organic tails. These hybrids show typical surfactant properties, with POMs acting as polar head groups and the hydrocarbon organic portions acting as hydrophobic tails. They form regular 23 or reverse 24 vesicles in different solvents controlled by the solvophobic interaction. In addition, a series of “dumbbell”-shaped POM-organic-POM hybrids have also been documented recently to display amphiphilic behavior and to form single-layer vesicular structures in solution. 26 Herein, studies are expanded to POM-containing fluorosur- factants comprising a hydrophilic POM “head group” and covalently linked hydrophobic, fluorinated “tails” in a single complex molecule. The fluorocarbon chains are known to be much more hydrophobic than hydrocarbon chains and have broad applications from Teflon to absorb oxygen gas. Hence, the self-assembly behaviors of such novel POM-containing fluorosurfactants in solution may contribute to the better understanding of their physicochemical properties and further facilitate the development of applications of such compounds. Here, two POM-containing fluorosurfactants involving hex- avanadate clusters bearing two fluorocarbon chains of different chain lengths are studied in solution. ■ EXPERIMENTAL SECTION Synthesis of POM-Containing Fluorosurfactants. Two hex- avanadate-containing fluorosurfactants are constructed by incorporat- ing two fluorocarbon tails into one Lindqvist-type polyoxovanadate (POV) [V 6 O 13 {(OCH 2 ) 3 CNH 2 }] 2 - , [( n -C 4 H 9 ) 4 N] 2 [V 6 O 13 {(OCH 2 ) 3 CNH(COO)CH 2 C 6 H 4 CH 2 CH 2 (CF 2 ) 5 - CF 3 } 2 ] 2- (TBA 2 ·6F-V 6 ) and [(n-C 4 H 9 ) 4 N] 2 [V 6 O 13 {(OCH 2 ) 3 CNH- (COO)CH 2 C 6 H 4 CH 2 CH 2 (CF 2 ) 7 CF 3 } 2 ] 2- (TBA 2 ·8F-V 6 ), respec- tively, as shown in Scheme 1. The detailed synthesis and character- ization are described in the Supporting Information. Received: September 26, 2016 Revised: November 3, 2016 Published: November 7, 2016 Article pubs.acs.org/Langmuir © 2016 American Chemical Society 12856 DOI: 10.1021/acs.langmuir.6b02308 Langmuir 2016, 32, 12856-12861