Characterization of Micron-Sized Periodic Structures in Multicomponent Polymer Blends by Ultra-Small-Angle Neutron Scattering and Optical Microscopy

The thermodynamic properties of a multicomponent blend containing nearly equal volume fractions of two homopolymers, a saturated polybutadiene with 89% 1,2-addition (component A) and polyisobutylene (component B), and 1 vol % of a diblock copolymer was studied by a combination of ultra-small-angle neutron scattering (USANS) and optical microscopy. The A−C diblock copolymer, which serves as a surfactant, has an A block that is chemically identical to the A homopolymer and a C block that is a saturated polybutadiene with 62% 1,2-addition. The C block exhibits attractive interactions with component B and repulsive interactions with component A. At temperatures between room temperature and 45 °C, USANS results indicated that this blend self-assembles into a microemulsion with periodic length scales in the 0.2−4 μm range. The USANS data were in excellent agreement with the Teubner−Strey equation for scattering from microemulsions. Optical microscopy studies revealed the presence of bicontinuous microemulsions with length scales that were commensurate with those obtained by USANS.