title: Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant.
abstract: We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.
authors: Department of Chemistry, Kyushu University, Fukuoka, Japan. annaka-scc@mbox.nc.kyushu-u.ac.jp
authors: Masahiko
authors: M
authors: Annaka
authors: Kanae
authors: K
authors: Morishita
authors: Satoshi
authors: S
authors: Okabe
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins / Q000737:chemistry*; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D055672:Static Electricity; D013501:Surface-Active Agents / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D011108:Polymers; D013501:Surface-Active Agents; C052970:poly-N-isopropylacrylamide; C006903:carbopol 940