POLYMERS IN COMPLEX FLUIDS - DYNAMIC AND EQUILIBRIUM PROPERTIES OF NANODROPLET-ABA BLOCK COPOLYMER STRUCTURES

Depending on the relative amount of hydrophilic A blocks (poly(oxyethylene)) and hydrophobic B block (polyisoprene), ABA block copolymers dissolved in water-in-oil microemulsions (H2O/AOT/isooctane) have been shown to form "core-shell" or "dimeric" complexes with the microemulsion nanodroplets. For both types of such complexes, the diffusional behavior as a function of the copolymer concentration is studied by using (H-1) pulsed field gradient spin-echo (PFGSE) NMR technique. A self-consistent picture of the size and geometrical shape of these structures has been established, and it is demonstrated that up to fairly large copolymer concentrations these results are compatible with the earlier reported viscosity and conductivity patterns in these systems. Inferring from the NMR results further interlinking of the nanodroplets upon increasing amounts of copolymer was evidenced by probing of larger (most likely) side-branched structures, which can be considered as the onset of a three-dimensional transient network (gel) as indicated by viscosity and conductivity patterns at very high copolymer concentrations.