Measurement of interfacial width in a poly(styrene)/poly(2-vinylpyridine) homopolymer blend by spatially resolved inelastic electron scattering

This research uses spatially resolved electron energy-loss spectroscopy (EE LS) in a scanning transmission electron microscope (STEM) to determine an u pper bound for the interfacial width of a solution-cast poly(styrene) (PS)- poly(2-vinylpyridine) (PVP) homopolymer blend. The measurement determines t he fraction of nitrogen as a function of position across an unstained inter face. The broadening effect of the incident-probe intensity distribution is deconvoluted from the raw data. In addition, a lower bound to the contribu tion of interfacial curvature to the interfacial width is estimated and als o separated from the measured data. This leads to an upper bound to the int erfacial width of 3.5 nm. The result is in agreement with independent measu rements by neutron scattering reported in the literature. Dose-resolved mea surements are made to demonstrate that the effects of mass loss during the present measurements are insignificant. Quantitative analysis of the carbon /nitrogen ratio is made on the basis of the background-subtracted C and N K -edges in PVP finding a value of 7.05 +/- 0.20, in agreement with the stoic hiometric value of 7.0.