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-pol ybutadiene (PB), and deuterated polystyrene (dPS), at 175 degrees C. To enh ance depth resolution, the top dPS layer is 'thinned' by ion sputtering, pr ior 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 stu dy, neutron reflectivity (NR) is used to determine the interfacial volume f raction profile between PB and an isotopic mixture of polystyrene (dPS:PS) having a dPS volume fraction of 0.30. After annealing at 175 degrees C, the interface broadens to 3.3 nm. However, no interfacial segregation of dPS o r PS is observed suggesting that the difference between the PB-dPS and PB-P S interaction parameters (chi) is insufficient to drive interfacial segrega tion. Using a self-consistent field model (SCF) and known values of chi, th e width is calculated to be 2.2 nm. By adding capillary wave broadening, th is width increases to 2.8 nm, in better agreement with the NR value. In agr eement with the NR measurement, the SCF model predicts no segregation of dP S or PS. (C) 1999 Elsevier Science Ltd. All rights reserved.