A comparison of atomic force microscope friction and phase imaging for the characterization of an immiscible polystyrene/poly(methyl methacrylate) blend film

Three different forms of atomic force microscope (AFM) measurement, topography, friction force and phase imaging, have been used to investigate the surface morphology and local composition of an immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend film. This sample forms discrete, micron-size domains in a continuous matrix, which is attributed to the segregation of PMMA in PS. When the samples were imaged in air, contrast in friction and phase images was caused by variations in sample topography only. When the samples were imaged under water, however, both friction and phase imaging yielded non-topographic contrast between domains. We ascribe the contrast in both of these imaging modes to preferential softening of the hydrophilic, PMMA-rich domains and to stronger tip–sample adhesive forces, highlighting the AFMʹs utility for probing local elastic properties and for compositional mapping of soft polymer samples.