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Triblock copolymers in a selective solvent: Dilute and semi‐dilute solutions
Author(s) -
Lairez Didier,
Adam Mireille,
Raspaud Eric,
Carton JeanPierre,
Bouchaud JeanPhilippe
Publication year - 1995
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19950900117
Subject(s) - polystyrene , copolymer , solvent , micelle , polymer chemistry , materials science , relaxation (psychology) , light scattering , neutron scattering , viscosity , dynamic light scattering , structure factor , thermodynamics , scattering , chemistry , composite material , polymer , aqueous solution , crystallography , organic chemistry , optics , physics , psychology , social psychology , nanoparticle , nanotechnology
Triblock copolymers polystyrene‐polyisoprene‐polystyrene were studied in dilute and semi‐dilute solutions in a selective solvent, i.e. a non‐solvent for polystyrene and a good solvent for polyisoprene. The mass of the copolymer is equal to 1.6×10 5 g/mol and it contains 70% of polyisoprene. At a concentration C equal to 1.6×10 −3 g/cm 3 triblock aggregation occurs. Experiments performed on dilute solutions 1 plead in favor of loose and polydisperse aggregates rather than spherical micelles: 1) the form factor of the aggregates shows a smooth decrease at qR<1; 2) internal modes are observed by quasi‐elastic light scattering; 3) specific viscosity measurements show that the internal concentration of unimers and aggregates are identical; 4) the unimer concentration and the aggregation number depend on the copolymer concentration. In semi‐dilute solutions 2 (C>3×10 −2 g/cm 3 ), dynamical properties are strongly affected by the temperature. Viscosity and longest relaxation time increase by a factor 10 5 as the temperature decreases from 50°C to 5°C, whereas the plateau modulus G remains independent of the temperature and proportional to the concentration. Small angle neutron scattering experiments reveal a cubic structure having a unit cell dimension d independent of the temperature and varying as C −1/3 leading to G∼1/d 3 . Quasi‐elastic light scattering experiments performed on this system show a wide relaxation function extending over 7 decades of time. These results argue for a lattice made of polystyrene nodes linked together by the polyisoprene middle blocks, the dynamics being governed by the glass transition of the nodes.