(458c) Electrostatic and Steric Stabilization of Nanoenergetics Suspensions

The US Army has an interest in developing Insensitive Munitions (IM) that can replace munitions in current use without jeopardizing performance and cost. Recently, methods that have been developed to decrease the sensitivity of energetic materials while keeping their performance involve reducing the size of the energetic material to nano scale. In the present work, one such method selected to produce nanoenergetic materials is bead milling, as it is highly scalable and easily controlled. During the milling process, the behavior of the product suspensions is increasingly influenced by particle-particle interactions, which can lead to undesirable outcomes such as agglomeration. Therefore if these interactions are better understood and controlled, higher nanoenergetics stability and quality could be achieved. Consequently, the main focus of this work relates to understanding the interaction forces of stabilization mechanisms of nanonitramines using electrostatic, steric and depletion techniques.

The RDX electrostatic stabilization mechanism was the aim of the first part of this work. The maximum Zeta potential is reached under alkaline conditions of Ph 11. The results indicate that the ionic strength, even at low concentrations of NaCl (0.002 mol/L), can increase the Zeta potential of the nanoRDX by 37%. The DLVO theory predicts that 300 nm RDX particles are stable at a low salt concentration of 0.002 mol/L and unstable at 0.1 mol/L. The turbidity test qualitatively confirms the results predicted by DLVO theory which shows that the nanoRDX dispersion is stabilized with the addition of electrolyte in an alkaline solution.

In the second part of this work, the polymeric stabilization of HMX using PVP polymer is investigated by zeta potential and turbidity measurements. This study showed that the solvent and the molecular weight affects the PVP adsorption. The turbidity test indicates that the stability is enhanced by increasing the ethanol concentration. Finally, an HMX milling study indicated that PVP in 50% water/ 50% ethanol was able to stabilize HMX by depletion and reduce the size to 180 nm within 10 minutes of milling. Strong aggregation was observed for HMX milled in the absence of PVP.

The present study will play an important role in the stabilization of nanoenergetics and will facilitate the manufacturing of nanoenergetics in a more effective and efficient manner at the production scale.