Predicted Anisotropic Thermal Conductivity for Crystalline 1,3,5‐Triamino‐2,4,6‐trinitobenzene (TATB): Temperature and Pressure Dependence and Sensitivity to Intramolecular Force Field Terms

Abstract

[a] 1IntroductionCharacterizationo fe nergy transport processes in molecular materials usinga ll-atom molecular dynamics( MD) simulations provides anecessaryand physical basis for the prediction and understanding of experimentally undetermined properties [1][2][3][4][5][6][7],m any of whicha re needed for the parameterization of the kinds of continuum-based mesoscale engineeringm odels widely used to simulate energetic materials [8][9][10][11][12][13][14][15]. Accurate predictionsf or anisotropic bulk material properties such as the thermal conductivity and rate coefficientsf or energyt ransfer processes are necessary if parameterized models are to yield reliable predictions for dynamic processes such as shock loading [9][10][11][12][14][15][16][17][18],h ot spot formation and relaxation [9-12, 14, 15, 19],a nd initiation of chemistry [11,14,19].R ecentM D-based predictions for the thermal conductivity of the insensitivem olecular crystalline explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) revealed significanta nisotropy for energy transport at T = 300 Ka nd P = 0.0 GPa [6,7].( Here and for all subsequent instances, pressures reported as 0.0 GPa formally correspond to 1atm, which is 0.0 GPa within the precision of our calculations.) Many other thermomechanical properties of TATB crystala lso exhibit significant anisotropy [20][21][22][23][24][25][26]. Anisotropy in TATB crystal physical properties is thought to be ac onsequence of the crystal packings tructure, which is triclinic and exhibits al ayered structure, wherein nearly planar TATB molecules form planar single-molecule-thick Abstract:T he anisotropic thermal conductivity of the layered molecular crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), an insensitive secondary high explosive, is determined using classicalm olecular dynamics on the P = 0.0 GPa isobar for temperatures 200 K T 700 Ka nd on the T = 300 Ki sotherm for pressures0 .0 GPa P 2.5 GPa. Sensitivity of the predicted( 300 K, 0.0 GPa) conductivity to intramolecular terms in the forcef ield is investigated.T wo conduction directions are considered, one nominally within and the other exactlyp erpendicular to the stackedp lanar single-molecule-thick layers comprising the TATB crystal. The thermal conductivity l(T,P)a long both directionsi s foundt od ecrease approximately as l / 1/T with increasing temperature and increase approximately linearly l / T with increasingp ressure. The temperature dependence is found to be highly anisotropic with nearly twice as large ar eduction in absolutec onductivity within the molecularl ayers (Dl = À0.67 Wm À1 K À1)c ompared to betweent hem (Dl = À0.35 Wm À1 K À1). Anisotropy in the conductivity is predicted to decrease with increasing temperature;t he P = 0.0 GPa conductivity is 68 %g reater within the layers than betweent hem at 200 K, but only 49 %g reater at 700 K. The pressure dependence is also anisotropic, with a5 1% and 76 %i ncrease in conductivity within and between the layers, respectively.P redictedv alues for the conductivity are found t...

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)

“…40 This force field was shown to approximately reproduce measured pressure-and temperature-dependent lattice parameters, 21 experimental vibrational spectra, 37 and the heat of sublimation. 24 It has been used for predictions of the isothermal elastic tensor, 23,24 basal plane plasticity, 24,29 nanoindentation response, 26 thermal conductivity, [37][38][39] energy transport away from a hot spot, 80 the melt curve, 81 and liquid-state transport coefficients. 81 It was also used as the basis for parameterizing an energy-conserving DPDE force model that was subsequently applied to study shock compression of (001)-oriented TATB on approximately the micron spatial scale.…”

“…21 A monoclinic polymorph, also layered, has been reported recently at room temperature for pressures greater than 4 GPa. 22 The high degree of structural anisotropy leads to significant anisotropy in the mechanical, [23][24][25][26][27][28][29][30][31][32][33][34] thermal, [35][36][37][38][39][40][41][42][43][44][45][46][47] and spectroscopic 21 properties of the substance. See Figure 1 for a view of a TATB crystal and additional information pertinent to the shock simulation geometry and crystal orientations studied here (detailed below).…”

Tandem Molecular Dynamics and Continuum Studies of Shock‐Induced Pore Collapse in TATB

“…The crystal is triclinic with two molecules per unit cell. The structure of the crystal is strongly anisotropic and this is reflected in pronounced anisotropy for many of the thermal [39][40][41][42][43][44][45][46][47][48][49][50], mechanical [51][52][53][54][55][56][57][58][59][60], and optical properties [61].…”

Phonon Lifetimes and Thermal Conductivity of the Molecular Crystal α-RDX

“…Furthermore, there exists a relative lack of knowledge regarding how thermal energy is conducted in van der-Waals bonded organic molecular crystals in relation to "simple" atomic crystalline materials such as Si or Ge. Highlighting the possible shortcomings of the existing kinetic theory for thermal transport in molecular crystals is the extremely low thermal conductivity of 𝛼-RDX, TATB, and 𝛽-HMX, ≤ 1 W/m⋅K, [5,6]. Such values are more akin to conductivities observed in amorphous or glassy materials than in atomic crystalline systems.…”