Morphologically Tunable Coassembly of Double Hydrophilic Block Polyelectrolyte with Oppositely Charged Fluorosurfactant Mariusz Uchman,* ,† Stergios Pispas, ‡ Lubomír Kova ́ c ̌ ik, § and Miroslav S ̌ tě pa ́ nek † † Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 40 Prague 2, Czech Republic ‡ Theoretical & Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635 Athens, Greece § Institute of Cellular Biology and Pathology, First Faculty of Medicine, Charles University in Prague, Albertov 4, 128 01 Prague 2, Czech Republic * S Supporting Information ABSTRACT: We report on the formation and structure development of polyelectrolyte-surfactant complexes, PE-S, of double hydrophilic block copolymers poly(sodium 2- sulfamate-3-carboxylate isoprene)-block-poly(ethylene oxide), PSCI - PEO, and cationic fl uorosurfactant, N - (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)- pyridinium chloride, HFDPCl. We compare the behavior of four PSCI-PEO samples differing in comonomer composition and polyisoprene block modification degree. Coassembled core-shell nanoparticles with the core formed by the PSCI/HFDPCl complex and the shell of PEO blocks were characterized by microscopic techniques (cryogenic transmission electron microscopy, atomic force microscopy) and by small-angle neutron scattering. Interactions between PSCI-PEO and HFDPCl were studied by isothermal titration calorimetry. We show that the bulky fluorosurfactant ions drive the coassembly toward structures with less curved interfaces such as cylindrical and wormlike micelles or vesicles. We also demonstrate the role of hydrophobic interactions in the system induced by the presence of unmodified polyisoprene units which in the case of the PSCI-PEO copolymer with a low degree of modification lead to formation of PSCI-PEO micelles and prevent the copolymer from the coassembly with HFDPCl. ■ INTRODUCTION The double hydrophilic block polyelectrolytes (DHBE) and oppositely charged surfactants (S) coassemble into a variety of stimuli-responsive complex nanostructures (PE-S) like spher- ical micelles, vesicles, or wormlike micelles that differ in their detailed structural organization and offer applications in pharmaceutical, cosmetic, and food industry as detergents or vessels for solubilization and delivery of various hydrophobic substances. 1-6 To design PE-S coassembled nanostructures with required properties, a number of factors have to be taken into account, such as the polyelectrolyte and/or the chemical structure and surfactant concentration, molecular weight, charge density, backbone rigidity, and degree of branching of the polyelectrolyte as well as the polarity of the headgroup and the length of the aliphatic tail of the surfactant. 1-6 Fluorosurfactants have proved to be promising contrast agents in 19 F magnetic resonance imaging ( 19 F MRI), and their complexes with polymers allow for tailored preparation of nanoparticles formulations with high payloads. 7-12 Despite that, only a few studies on the formation of DHBEs and fluorosurfactants complexes have been performed so far, 11,12 and only little more is known about interaction of homopolymers and fluorosurfactants in solution. 13 In contrast, complexes of DHBE with hydrocarbon surfactants have been studied extensively. 1-6,14-21 Interestingly, Laschewsky et al. 11 reported that the coassembly of perfuorodecanoic acid and DHBE containing cationic poly(trimethylammonium ethylacrytate) blocks lead to the formation of elliptical core-shell particles with the cores consisting of segregated lamellae of the fluorocarbon chains and polyelectrolyte the blocks. All the steps for the preparation of the above-mentioned nanoparticles were carried out in water and offer great potential for in vivo applications of such formulations. Such a strategy has a great advantage as compared to nanoparticles of amphiphilic block copolymers that are usually prepared using organic cosolvent and dialysis. More recently, Wang and co-workers investigated association complexes of poly(ethylene glycol)-b-poly(sodium glutamate) (PEG 113 -PGlu 50 and PEG 113 -PGlu 100 ) and dodecyltrimethy- lammonium bromide surfactant (DTAB). 21 Differences in the association nanostructures, e.g., spherical and wormlike aggregates in PEG 113 -PGlu 50 /DTAB mixture and vesicular aggregates in PEG 113 -PGlu 100 /DTAB mixture, were explained Received: March 26, 2014 Revised: September 4, 2014 Article pubs.acs.org/Macromolecules © XXXX American Chemical Society A dx.doi.org/10.1021/ma500622a | Macromolecules XXXX, XXX, XXX-XXX