Cohesive Hamaker Constants and Dispersive Surface Energies of RDX, PETN, TNT, and Ammonium Nitrate‐Based Explosives

Abstract

[a] 1IntroductionAf undamentalu nderstanding of the adhesionb etween explosives residues, swabs used during detection of these residues, and surfaces to which the residues adhere is necessary to optimize the detection of these residues in airport security settings. The basic forcest hat control the behavioro f the residues are the van der Waals (vdW)f orces, whichc an be considered to be comprised of Keesom (dipole-dipole interactions), Debye (dipole-induced dipole interactions), and London dispersion forces( induced dipole-induced dipole interactions). The Hamaker constant A estimates the magnitude of vdW forcesb etweent wo dissimilar materials or within ap ure material [1].A dhesive Hamaker constants betweenm aterials i and k in medium j are denoted as A ijk while cohesive Hamaker constants for material i in a vacuum are denoteda sA ii .U sing combining rules established by Israelachvili [1],f amilies of A ii can be used to estimate A ijk amongavariety of materials in varying media. As ar esult, A ii of explosivesr esidues allow prediction of A ijk 's (and correspondingly the strengtho fa dhesion) between these residues and commonly swabbed surfaces.Methods of predicting A ii using Hamaker's pair-wise additive approach [2]

An evaluation of complementary approaches to elucidate fundamental interfacial phenomena driving adhesion of energetic materials

“…Equation 6 was used to estimate the Hamaker constants of the materials from the measured surface energy values ( Figure 4). The PETN, RDX and TNT results of both this analysis and the IGC analysisare within the error of the Hamaker constants determined via Lifshitz theory [16]. TheLifshitz-predicted Hamaker constantsare consistently higher than the IGC-predicted Hamaker constantsas the IGC analysis does not take into account the polar surface energy component in the interaction.…”

“…Surface energy and surface energy components of the energetic materials. The dispersive surface energy components from this study compare well to the dispersive surface energy determined through the IGC method[16]. The dispersive component dominates for each of the films studied.…”

“…The contact angle results for PETN, TNT, and RDX results were compared to adhesion constants previously determined using IGC and Lifshitz theory [16]. Hamaker constants have been readily employed regardless of origin [5].…”

“…Additionally, crystal faces fracture or deform during compaction, and compaction of sensitive energetics for contact angle measurements can be a safety concern.As a result, 1,3,5-triamino-2,4,6-trinitrobenzene(TATB), an insensitive high explosive, is the only energetic powder that has been compacted for contact angle measurements [9,10].Contact angle measurements have been performed on crystalline pentaerythritoltetranitrate (PETN) (two different crystal faces) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) single crystals, but the experimental details were not reported [11]. The Owens and Wendt method was used to relate the contact angles measured on the RDX in these studies to the surface energy of the RDX [12].IGC experiments have been performed onenergetic materials, including PETN, 2,4,6-trinitrotoluene(TNT), RDX, and1,3,5,7-tetranitro-1,3,5,7tetraazacyclooctane(HMX) [13][14][15][16], including arecent study that determined the dispersive surface energy of PETN, TNT, and RDX and related theseto cohesive Hamaker constants [16].In order to overcome the challenges associated with contact angle measurements and to obtain a comprehensive database of adhesion constants, thin films produced by physical vapor deposition will be used for contact angle measurements.…”

The Effect of Ionic Strength and pH on the Electrostatic Stabilization of NanoRDX

“…where n 1 and n 2 are the indices of refraction of RDX and water, w e is the electronic adsorption frequency (assumed to be 3 Â 10 15 s À1 Þ, as reported by Israelachvili [19], e 1 and e 2 are the dielectric constants of RDX and water. Harrison measured the Hamaker constant of RDX using inverse gas chromatography technique and showed that the experimental results agree with the prediction of Eq.4 within the model error [20].…”