Rheological properties of suspensions of polyethylene-coated aluminum nanoparticles

Ultrafine aluminum powder was identified as very promising fuels for novel energetic materials formulations. However, the large specific surface area of this powder facilitates its oxidation and greatly reduces its shelf life. Therefore, different coating processes were proposed to solve this problem. The rheology of viscous suspensions of nanoparticles still remains poorly understood and the effect of the coating of such particles on the flow behavior is even more difficult to assess. We have studied the rheology of ultrafine aluminum suspensions in three low molecular weight polymers of different viscosities: a hydroxy-terminated polybutadiene, a polypropylene glycol, and a polysiloxane. The nanosize aluminum powder was previously coated by a thin layer of high-density polyethylene using an in situ polymerization process. The rheological characterization of the suspensions was conducted by the means of steady and oscillatory shear flow measurements for noncoated and coated particles. The effect of the coating process on the rheology of the suspensions is discussed in terms of the interactions between the particles and the suspending fluids.