Nanoparticle Organization by Growing Polyethylene Crystal Fronts

We investigate the crystallization-induced ordering of C₁₈ grafted 14 nm diameter spherical silica nanoparticles (NPs) in a short chain (M_w = 4 kDa, Đ_M ≈ 2.3) polyethylene and a commercial high-density polyethylene (M_w = 152 kDa, Đ_M ≈ 3.2) matrix. For slow isothermal crystallization of the low molecular weight matrix, the NPs segregate into the interlamellar regions. This result establishes the generality of our earlier work on poly(ethylene oxide) based materials and suggests that crystallization can be used to control NP dispersion across different polymer classes. The incompatibility between the particles and the matrix in the M_w = 152 kDa results in a competition between filler organization and filler agglomeration. The mechanical properties improve due to the addition of NPs and are further enhanced by particle organization, even for the case of the macrophase-separated mixtures in the M_w = 152 kDa matrix. In contrast, dielectric behavior is strongly affected by the scale of NP organization, with the lower molecular weight matrix showing more significant increases in permittivity due to the local scale of NP ordering.