Crystallization-induced Ordering in Poly(ethylene oxide)-Silica Nanocomposites: Modifying Particle Diffusivity

Semicrystalline polymers make up over two-thirds of the world’s produced polymers and while these materials have a range of applications they are limited by their generally low modulus. We have previously shown that one strategy to improve the material modulus is to use crystallization to order silica nanoparticles into the amorphous regions of the semicrystalline hierarchy. This anisotropic ordering is controlled by the velocity of the crystal growth front relative to the diffusive rate of the nanoparticles. While the previous study has demonstrated the ability to order nanocomposites at slow enough crystallization speeds, we now wish to understand the role of particle diffusivity on the ordering process. To examine this role we used silica nanoparticles in four molecular weights of Poly(ethylene oxide) ranging from 5.4 – 46 kDa. By manipulating the molecular weight of the matrix, we primarily affect the viscosity of the melt allowing for increased particle diffusion in the lower molecular weight polymers. We then quantify the ordering using the Herman’s Orientation function on x-ray scattering images. We see that the ordering is maximized at intermediate crystal growth speeds which suggests interspherullitic segregation at very slow growth speeds.