Interfaces in polymer blends

We investigate the structure and thermodynamics of interfaces in dense poly mer blends using Monte Carlo (MC) simulations and self-consistent held (SCF ) calculations. For structurally symmetric blends we find quantitative agre ement between the MC simulations and the SCF calculations for excess quanti ties of the interface (e.g., interfacial tension or enrichment of copolymer s at the interface). However, a quantitative comparison between profiles ac ross the interface in the MC simulations and the SCF calculations has to ta ke due account of capillary waves. While the profiles in the SCF calculatio ns correspond to intrinsic profiles of a perfectly fiat interface the local , interfacial position fluctuates in the MC simulations. We test this conce pt by extensive Monte Carlo simulations and study the cross-over between "i ntrinsic" fluctuations which build up the local profile and capillary waves on long (lateral) length scales. Properties of structurally asymmetric blends are exemplified by investigati ng polymers of different stiffness. At high incompatibilities the interfaci al width is not much larger than the persistence length of the stiffer comp onent. In this limit we iind deviations from the predictions of the Gaussia n chain model: while the Gaussian chain model yields an increase of the int erfacial width upon increasing the persistence length, no such increase is found in the MC simulations. Using a partial enumeration technique, however , we can account for the details of the chain architecture on all length sc ales in the SCF calculations and achieve good agreement with the MC simulat ions. In blends containing diblock copolymers we investigate the enrichment of co polymers at the interface and the concomitant reduction of the interfacial tension. At weak segregation the addition of copolymers leads to compatibil ization. At high incompatibilities, the homopolymer-rich phase can accommod ate only a small fraction of copolymer before the copolymer forms a lamella r phase. The analysis of interfacial fluctuations yields an estimate for th e bending rigidity of the interface. The latter quantity is important for t he formation of a polymeric microemulsion at intermediate segregation and t he consequences for the phase diagram are discussed.