Acoustic Field-Assisted Nanoparticle Ordering in Poly(ethylene oxide) Nanocomposites

Prior work has shown that nanoparticle (NP) organization within the interlamellar regions of semicrystalline polymers can be achieved below a critical crystallization rate defined by an appropriate Péclet number, Pe = aG/D, where a is the characteristic NP transport distance, G is the crystal growth rate, and D is the NP diffusivity. NPs can redistribute ahead of the advancing crystallization front and become organized within the interlamellar regions with the most pronounced NP ordering occurring when Pe ≈ 1. We demonstrate, using small-angle X-ray scattering (SAXS) and electron microscopy, that the application of an external acoustic field increases the temperature range (i.e., the supercooling) over which NPs can be ordered by crystallization thereby shifting the kinetic boundary for crystallization-induced ordering and expanding the accessible processing window. Analysis using the Péclet-number framework indicates that acoustic excitation enhances effective NP transport relative to the advancing crystallization front. Acoustic excitation therefore provides a means of controlling NP morphology without substantially altering the bulk crystalline fraction or melting temperature of the polymer matrix.