Thermodynamic and Kinetic Aspects of Coassembly of PEO−PMAA Block Copolymer and DPCl Surfactants into Ordered Nanoparticles in Aqueous Solutions Studied by ITC, NMR, and Time-Resolved SAXS Techniques Mariusz Uchman,* ,† Michael Gradzielski, § Borislav Angelov, ∥ Zdenek Tos ̌ ner, ‡ Joongseok Oh, ⊥ Taihyun Chang, ⊥ Miroslav S ̌ tě pa ́ nek, † and Karel Procha ́ zka † † Department of Physical and Macromolecular Chemistry and ‡ NMR Laboratory, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 40 Prague 2, Czech Republic § Stranski Laboratorium fü r Physikalische und Theoretische Chemie, Technische Universitä t Berlin, Straβe des 17. Juni 124, 10623 Berlin, Germany ∥ Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky ́ Square 2, 16206 Prague 6, Czech Republic ⊥ Department of Chemistry and Division of Advance Materials Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea * S Supporting Information ABSTRACT: The electrostatic coassembly of a block copolymer polyelectrolyte poly(ethylene oxide-block-poly- (methacrylic acid), PEO 705 −PMAA 476 , and oppositely charged surfactant, N-dodecylpyridinium chloride (DPCl), has been investigated by a combination of isothermal titration calorimetry (ITC), spin-echo NMR spectroscopy, and time- resolved SAXS measurements. The study (i) confirms the conclusions drawn from our earlier study [Macromolecules 2012, 45, 6474] by scattering and microscopy techniques (i.e., the ITC curves can be interpreted using arguments consistent with conclusions of the earlier study) and (ii) yields new insight into the thermodynamic and kinetic behavior of the self-assembling system. The most important finding obtained by stopped-flow time-resolved SAXS measurements concerns the surprisingly high rate of processes of creation of structurally ordered cores of self-assembled surfactant−polyelectrolyte nanoparticles (<50 ms). ■ INTRODUCTION Self-assembled polymeric nanoparticles and nanostructured materials find a number of applications in everyday life of human society. An important class of these materials are the self-assemblies formed as a result of electrostatic interactions. The terms like interpolyelectrolyte complexes (IPEC), block ionomer complexes (BIC), complex coacervate core micelles (C3Ms), and complex polyions have been used in recent years to describe electrostatic complexation between oppositely charged high-molar-mass species. Since the pioneering work of Kataoka and Kabanov on IPEC, 1,2 this subject has been attracting great interest of many research groups due, in part, to the curiosity-driven fundamental research and to promising potential applications of such formulations in, e.g., cosmetics, food technology, and drug delivery. 3−10 The considerable theoretical and experimental effort of researchers resulted in hundreds of papers published on this subject, so it is futile to try to list all relevant articles and it is why we included only a limited number of review papers that appeared recently and are relevant for this study. 3−10 The formation of electrostatic complexes involves interplay of electrostatic and hydrophobic interactions which control the coassembly of polyelectrolyte−surfactant (PE−S) complexes. Hence, a targeted tuning of molecular characteristics like molar mass, charge density, backbone rigidity, and degree of branching of the polyelectrolyte as well as the length of the aliphatic tail, polarity of the headgroup, and different surfactant architectures (single, double, triple tail) allows one to design and prepare materials with required properties. 10−19 Because the entropy increase due to release of small counterions in bulk solution is the main driving force of the process, the ionic strength of the solution has a very important effect on the Received: December 5, 2012 Revised: February 26, 2013 Article pubs.acs.org/Macromolecules © XXXX American Chemical Society A dx.doi.org/10.1021/ma302503w | Macromolecules XXXX, XXX, XXX−XXX