Parameters determined from binary experiments were used to predict the behavior of multicomponent A/B/A-C polymer blends, where A is saturated polybutadiene with 90% 1,2-addition (sPB90), B is polyisobutylene (PIB), and C is also saturated polybutadiene but with 63% 1,2-addition (sPB63). The polymers were chosen such that the binary interactions (A/B, A/C, and B/C) are analogous to those in oil (A)/water (B)/nonionic surfactant (A-C) systems, where A/B and A/C are unfavorable interactions (χ > 0) and B/C is a favorable interaction (χ < 0). The Flory-Huggins interaction parameters (χ AB, χAC, and χBC) and the statistical segment lengths (lA, lB, and lC) were all determined experimentally by fitting the random phase approximation (RPA) to small-angle neutron scattering (SANS) data from the three binary homopolymer blends. These parameters were successfully used to predict the scattering from concentration fluctuations in a homogeneous A/B/A-C blend using multicomponent RPA. These same binary parameters were also used as the only inputs to self-consistent field theory (SCFT) calculations of ordered multicomponent polymer blends. The SCFT calculations enabled quantitative interpretation of the SANS profiles from microphase separated A/B/A-C blends. The phase separation temperatures predicted by theory for the blends were within the experimental error, and the theoretical domain spacings were within 10% of the experimental values.
A balanced A-C diblock copolymer surfactant was used to organize mixtures of immiscible A and B homopolymers. The C block of the copolymer exhibits repulsive and attractive interactions with the A and B homopolymers, respectively, leading to rich phase behavior. Experimental results indicate the existence of a microphase-separated state at low temperatures, a homogeneous phase at intermediate temperatures, and macrophase separation at high temperatures. It is unusual for a microphase-separated blend to exhibit a homogeneous phase prior to macrophase separation. In this study, component A was saturated polybutadiene with 89% 1,2-addition, component B was polyisobutylene, block A of the diblock copolymer was chemically equivalent to component A, and block C of the diblock copolymer was saturated polybutadiene with 63% 1,2-addition. We use a combination of Flory-Huggins theory (FHT), self-consistent field theory (SCFT) and the random-phase approximation (RPA) to understand the origin of our observations. All of the parameters needed for the SCFT, FHT, and RPA calculations were obtained from independent measurements. The measured length scale of the periodic concentration fluctuations in the homogeneous state and the domain spacing of the microphase-separated blends were in close agreement with RPA and SCFT, respectively. The transition temperatures between phases predicted with theory were in reasonable agreement with the experimental measurements.
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