Study On Self-assembly Of Porous Spherical LLM-105

With the development of the times,the international environment is becoming more and more complicated,and the requirements of the slapper detonator are becoming higher and higher.It is the key for the new generation slapper detonator is the selection of primary explosives with low-sensitivity and high-energy,such as 2,6-diamino-3,5-dinitropyrazine-1-oxide(LLM-105).LLM-105 is a kind of high-energy and low-sensitivity explosive,but it is difficult to be detonated by flyer plate of the slapper detonator,so it is needs to be modified.It is a usual way to prepare LLM-105 into ultrafine particles;the detonation reliability is higher with the decrease of particle size.However,the ultrafine particles are easy to agglomerate after long-term storage,and particles with smaller sizes are more likely to agglomerate,leading to lower detonation reliability after long-term storage.The key of solving the conflict is to prevent the ultrafine particles from agglomerating in long-term storage.Therefore,the preparation of porous LLM-105 spherulites with sea-urchin-shaped morphology was described.Porous LLM-105 spherulites with sea urchin-like morphology were prepared by the solvent-antisolvent method.The influence of some crystallization parameters on the morphology of porous LLM-105 spherulites was studied,such as surfactant,stirring speed,stirring time,crystallization temperature and other experimental parameters.The preparation process of porous LLM-105 spherulites is as follows:Raw LLM-105(0.2 g)was dissolved in DMSO(5 mL)at 60℃.Ethyl acetate(100 mL)and PVP(0.2 g)were added to a round bottom flask at 0℃.Then,the LLM-105 solution in which the raw LLM-105 was dissolved was dropped into the round bottom flask within 1 minute and stirring was started at 600r/min.After 30 minutes,the stirring was stopped;the resulting mixture was filtered by suction and washed several times with deionized water.The resulting LLM-105 crystals were firstly dried in air for over 4 h and in vacuum for 6 h at 80℃for inspection.In order to understand the self-assembly mechanism of porous LLM-105,the LLM-105crystals with different stirring times were sampled and analyzed,and the double layer structure of PVP and LLM-105 crystal plane was studied by molecular dynamics calculations,and the morphology of LLM-105 after PVP effect was predicted.The simulation results show that PVP is strongly adsorbed on the(0 2 0)face,which inhibits the growth of the(0 2 0)face,which eventually leads to the formation of flaky parallelogram-like crystal.Large amounts of experimental results demonstrate that PVP induces the formation of X-shaped crystals,and LLM-105 self-assembles into porous spherulites on the basis of X-shaped crystals.X-shaped crystals have a relatively high concentration of LLM-105 at smaller included angles,and X-shaped crystals provide a new growth step for the later-grown branches,so a large number of small-angled branches with symmetry were gradually formed,eventually formed porous LLM-105 spherulites.The structure of porous LLM-105 spherulites was characterized by scanning electron microscopy(SEM),X-ray powder diffraction(XRD),Fourier infrared(FT-IR)spectrometer,and nuclear magnetic resonance(~1H NMR)spectrometer,and the thermal properties and explosion properties were obtained by TG-DSC and calorimetric experiments.The results show that porous LLM-105 spherulites did not undergo a chemical reaction during the crystallization process,and its crystal form did not change;the thermal decomposition peak temperature of porous LLM-105 spherulites was about 5℃higher than that of raw LLM-105,and the initial thermal decomposition temperatures of the porous LLM-105spherulites were lower than those of the raw LLM-105.The thermal decomposition apparent activation energy of raw LLM-105 and porous LLM-105 were calculated as 218.08 kJ/mol and 208.61 kJ/mol,separately.The constant volume combustion energy of porous LLM-105spherulites was-9954.33 J/g,the standard molar enthalpy of formation was-6.318 kJ/mol.When density was constant at 1.6 g/cm~3,the detonation pressure and detonation velocity of porous LLM-105 spherulites were 21.997 GPa and 7.305 km/s,respectively.Compared with HNS,TATB and HMX,porous LLM-105 spherulites are a preferred explosives as primary explosives for the new generation slapper detonator.