A supramolecular polymer brush composed of polyvinytpyrrolidone-cholesterol(PVP-Chol)was fabricated based on intermolecular hydrogen bonding between the ketone groups of the PVP moieties and the hydroxyl groups of the...A supramolecular polymer brush composed of polyvinytpyrrolidone-cholesterol(PVP-Chol)was fabricated based on intermolecular hydrogen bonding between the ketone groups of the PVP moieties and the hydroxyl groups of the cholesterol,both in solution and at the air/water interface.These confirmations were confirmed by Fourier transform infrared(FT-IR)spectroscopy,surface pressure versus molecular area(E-A)isotherms,and atomic force microscopy(AFM).At surface pressures up to 2.5 mN·m^(-1),the interfacial film was composed of cholesterol-enriched regions and PVP-Chol nanofibril domains.Interestingly,oversurface pressures,the structure of the PVP-Chol-enriched domains evolved frominitial irregular shapes,to crescent and heart-shaped zones,and then to circular shapes.This transition indicated the controllability of such domains during compression of a complex monolayer at relatively low surface pressures.Above 2.5 mN·m^(-1),the circular PVP-Chol domains disappeared and fibrous aggregates were formed at the air/water interface.The height of the comb-like PVP-Chol nanofibrils could be reversibly varied between approximately 4.3 and 1.8 nm by adjusting the voltage applied to piezoceramics during the AFM scanning process.These results demonstrate that the reversible structural transformation of the PVP-Chol complex from cylindrical to elliptic cylindrical is induced by the applied force of the AFM tip up to a value of 1.0 mN·m^(-1).These data provide important and useful information that improves our understanding of the relationship between the structures and performances of supramolecular polymer brushes,and should extend the range of applications of chotesterol-functionalized polymers fabricated via a simple mixing strategy.展开更多
By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations,the structural evolution and stability of TATB under shock compression was investigated.Due to the im...By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations,the structural evolution and stability of TATB under shock compression was investigated.Due to the improvement in synchronization control between two-stage light gas gun and the transient Raman spectra acquisition,as well as the sample preparation,the Raman peak of the N-O mode of TATB was firstly observed under shock pressure up to 13.6 GPa,noticeably higher than the upper limit of 8.5 GPa reported in available literatures.By taking into account of the continuous shift of the main peak and other observed Raman peaks,we did not distinguish any structural transition or any new species.Moreover,both the present Raman spectra and the time-resolved radiation of TATB during shock loading showed that TATB exhibits higher chemical stability than previous declaration.To reveal the detailed structural response and evolution of TATB under compression,the density functional theoretical calculations were conducted,and it was found that the pressure make N-O bond lengths shorter,nitro bond angles larger,and intermolecular and intra-molecular hydrogen bond interactions enhanced.The observed red shift of Raman peak was ascribed to the abnormal enhancement of H-bound effect on the scissor vibration mode of the nitro group.展开更多
Cubic boron nitride(CBN)micro powders and mixture of CBN micro powders with Al or Ti powders were fast heated at 1300,1400,1450,1500℃,and then kept for 5 min under spark plasma sintering(SPS).The obtained powders wer...Cubic boron nitride(CBN)micro powders and mixture of CBN micro powders with Al or Ti powders were fast heated at 1300,1400,1450,1500℃,and then kept for 5 min under spark plasma sintering(SPS).The obtained powders were analyzed with XRD.The results show that,simple CBN kept cubic structure after heated at 1300℃;when the temperature rose to 1400℃,some CBN was transformed into hexagonal structured boron nitride(hBN).As for CBN micro powders mixed with aluminum or titanium micro powders,the onset transforming temperature of CBN to hBN get raised.This results indicated that the structural transformation of boron nitride begun from the surface of CBN crystal particle,different coexist elements affect the surface situation of CBN particles.As the stabilities of CBN crystal particle surface improved,the onset structural transform temperature of CBN was also increased.展开更多
Crystal structure evolution of energetic crystals under external stimuli can significantly change their chemical/physical properties and profoundly impact the effectiveness and safety of weapon systems.In this study,t...Crystal structure evolution of energetic crystals under external stimuli can significantly change their chemical/physical properties and profoundly impact the effectiveness and safety of weapon systems.In this study,the evolution of the crystal structure of the high explosive 1,3,5-trinitro-1,3,5-triazine(Cyclotrimethylenetrinitramine,RDX)is investigated within the temperature range of−100℃–100℃ using in situ single-crystal X-ray diffraction technology.The thermal expansion rates of unit cell along the crystal axes and the inter-layer spacings of the mainly exposed crystal planes(111),(210)and(021)are calculated.Compared to the linear expansion of the unit cell,the increase of the atomic thermal vibrations,described by atomic displacement parameter(ADP),of RDX follows an exponential function.The ADP of the nitro group increases much faster than those of the central ring,especially at high temperatures,which is considered to be the cause of the molecular decomposition of RDX,and is consistent with calculation results identifying the−NO₂bond as the trigger of explosive decomposition.A tendency from AAE to AAA conformation is found for the RDX molecule,according to the orientation angle change of the nitro groups relative to the central ring,which causes the compression of the central ring.By comparing the crystal structure evolution behavior of RDX with HMX,it is concluded that the smaller unit cell expansion,the stronger atomic vibration and the lower molecular deformation ability of RDX are not conducive to buffering external energy,which are the main reason for the lower thermal stability,higher mechanical sensitivity and absence of phase transition before thermal decomposition of RDX,compared to HMX.These results will provide a promising way to characterize the crystal structure evolution of energetic materials for the comprehensive understanding of their properties and performance at the atomic and molecular levels.展开更多
基金supported by the National Natural Science Foundation of China(21273074,21576079,91334203,21476070)the 111 Project of Ministry of Education of China(B08021)
文摘A supramolecular polymer brush composed of polyvinytpyrrolidone-cholesterol(PVP-Chol)was fabricated based on intermolecular hydrogen bonding between the ketone groups of the PVP moieties and the hydroxyl groups of the cholesterol,both in solution and at the air/water interface.These confirmations were confirmed by Fourier transform infrared(FT-IR)spectroscopy,surface pressure versus molecular area(E-A)isotherms,and atomic force microscopy(AFM).At surface pressures up to 2.5 mN·m^(-1),the interfacial film was composed of cholesterol-enriched regions and PVP-Chol nanofibril domains.Interestingly,oversurface pressures,the structure of the PVP-Chol-enriched domains evolved frominitial irregular shapes,to crescent and heart-shaped zones,and then to circular shapes.This transition indicated the controllability of such domains during compression of a complex monolayer at relatively low surface pressures.Above 2.5 mN·m^(-1),the circular PVP-Chol domains disappeared and fibrous aggregates were formed at the air/water interface.The height of the comb-like PVP-Chol nanofibrils could be reversibly varied between approximately 4.3 and 1.8 nm by adjusting the voltage applied to piezoceramics during the AFM scanning process.These results demonstrate that the reversible structural transformation of the PVP-Chol complex from cylindrical to elliptic cylindrical is induced by the applied force of the AFM tip up to a value of 1.0 mN·m^(-1).These data provide important and useful information that improves our understanding of the relationship between the structures and performances of supramolecular polymer brushes,and should extend the range of applications of chotesterol-functionalized polymers fabricated via a simple mixing strategy.
基金supported by the National Natural Science Foundation of China(Grant Nos.12072299,11902276)the Natural Science Foundation of Sichuan Province(Grant No.2022NSFSC1802)+1 种基金the Basic Research Project of Southwest Jiaotong University(Grant No.2682023ZTPY009)the National Key Laboratory for Shock Wave and Detonation Physics of China(Grant No.JCKYS2019212007)。
文摘By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations,the structural evolution and stability of TATB under shock compression was investigated.Due to the improvement in synchronization control between two-stage light gas gun and the transient Raman spectra acquisition,as well as the sample preparation,the Raman peak of the N-O mode of TATB was firstly observed under shock pressure up to 13.6 GPa,noticeably higher than the upper limit of 8.5 GPa reported in available literatures.By taking into account of the continuous shift of the main peak and other observed Raman peaks,we did not distinguish any structural transition or any new species.Moreover,both the present Raman spectra and the time-resolved radiation of TATB during shock loading showed that TATB exhibits higher chemical stability than previous declaration.To reveal the detailed structural response and evolution of TATB under compression,the density functional theoretical calculations were conducted,and it was found that the pressure make N-O bond lengths shorter,nitro bond angles larger,and intermolecular and intra-molecular hydrogen bond interactions enhanced.The observed red shift of Raman peak was ascribed to the abnormal enhancement of H-bound effect on the scissor vibration mode of the nitro group.
基金support provided by Natural Science Foundation of Hebei Province(No.E 2006000226)
文摘Cubic boron nitride(CBN)micro powders and mixture of CBN micro powders with Al or Ti powders were fast heated at 1300,1400,1450,1500℃,and then kept for 5 min under spark plasma sintering(SPS).The obtained powders were analyzed with XRD.The results show that,simple CBN kept cubic structure after heated at 1300℃;when the temperature rose to 1400℃,some CBN was transformed into hexagonal structured boron nitride(hBN).As for CBN micro powders mixed with aluminum or titanium micro powders,the onset transforming temperature of CBN to hBN get raised.This results indicated that the structural transformation of boron nitride begun from the surface of CBN crystal particle,different coexist elements affect the surface situation of CBN particles.As the stabilities of CBN crystal particle surface improved,the onset structural transform temperature of CBN was also increased.
基金supported by the National Natural Science Foundation of China(Grant Nos.21875232 and 11704349)。
文摘Crystal structure evolution of energetic crystals under external stimuli can significantly change their chemical/physical properties and profoundly impact the effectiveness and safety of weapon systems.In this study,the evolution of the crystal structure of the high explosive 1,3,5-trinitro-1,3,5-triazine(Cyclotrimethylenetrinitramine,RDX)is investigated within the temperature range of−100℃–100℃ using in situ single-crystal X-ray diffraction technology.The thermal expansion rates of unit cell along the crystal axes and the inter-layer spacings of the mainly exposed crystal planes(111),(210)and(021)are calculated.Compared to the linear expansion of the unit cell,the increase of the atomic thermal vibrations,described by atomic displacement parameter(ADP),of RDX follows an exponential function.The ADP of the nitro group increases much faster than those of the central ring,especially at high temperatures,which is considered to be the cause of the molecular decomposition of RDX,and is consistent with calculation results identifying the−NO₂bond as the trigger of explosive decomposition.A tendency from AAE to AAA conformation is found for the RDX molecule,according to the orientation angle change of the nitro groups relative to the central ring,which causes the compression of the central ring.By comparing the crystal structure evolution behavior of RDX with HMX,it is concluded that the smaller unit cell expansion,the stronger atomic vibration and the lower molecular deformation ability of RDX are not conducive to buffering external energy,which are the main reason for the lower thermal stability,higher mechanical sensitivity and absence of phase transition before thermal decomposition of RDX,compared to HMX.These results will provide a promising way to characterize the crystal structure evolution of energetic materials for the comprehensive understanding of their properties and performance at the atomic and molecular levels.
