The interface between immiscible polymers studied by low-energy forward recoil spectrometry and neutron reflectivity

The superb depth resolution of low-energy, forward recoil, spectrometry, (LE-FRES), is demonstrated by measuring the interfacial profile between 1,4-polybutadiene (PB), and deuterated polystyrene (dPS), at 175°C. To enhance depth resolution, the top dPS layer is ‘thinned’ by ion sputtering, prior to LE-FRES analysis, to achieve a resolution of 13 nm at the interface. An interfacial width of 6.0±3.5 nm is measured. To compliment this study, neutron reflectivity (NR) is used to determine the interfacial volume fraction profile between PB and an isotopic mixture of polystyrene (dPS:PS) having a dPS volume fraction of 0.30. After annealing at 175°C, the interface broadens to 3.3 nm. However, no interfacial segregation of dPS or PS is observed suggesting that the difference between the PB–dPS and PB–PS interaction parameters (χ) is insufficient to drive interfacial segregation. Using a self-consistent field model (SCF) and known values of χ, the width is calculated to be 2.2 nm. By adding capillary wave broadening, this width increases to 2.8 nm, in better agreement with the NR value. In agreement with the NR measurement, the SCF model predicts no segregation of dPS or PS.