Inelastic Brillouin light scattering from semicrystalline polypropylene films reveals the
presence of up to four bulk and surface phonons. The coexistence of amorphous and crystalline regions
in the micrometer range allows for the propagation of two longitudinal acoustic excitations and one
transverse acoustic excitation. The surface Rayleigh wave proceeds with a phase velocity intermediate
between the two longitudinal counterparts, indicating surface inhomogeneities. The intensity and the
frequency of the observed phonons relate to the fraction of sizable (>0.2 μm) spherulites and provide a
nondestructive microrheological characterization of the film. The relation of the acoustic excitations to
the surface and bulk morphology of the semicristalline films is supported by the X-ray patterns and
AFM images.
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