Smart Functional Nanoenergetic Materials

Transcription

1 Smart Functional Nanoenergetic Materials Graphene as a Reactive Material and Carrier of Energetic Materials I. A. Aksay, A. Selloni, R. Car, C. Zhang, D. M. Dabbs Chemical and Biological Engineering and Chemistry Princeton University, Princeton, NJ N. Kumbhakarna, S. T. Thynell, R. A. Yetter Mechanical and Nuclear Engineering PennState University, University Park, PA J. B. DeLisio and M.R. Zachariah Mechanical Engineering University of Maryland, College Park, MD 20742

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3 Splitting of Graphite into Single Sheets M.J. McAllister et al., Chem. Materials (2007) Graphite Oxide by Staudenmaier method (1898) 4 fold volume expansion Thermal expansion (>500 fold) at 1050 C Boehm (1962) SA ~850 m 2 /g by BET and >1800 m 2 /g by methylene blue adsorption in solvents Disappearance of graphite peaks after oxidation and elimination of all peaks after expansion >80% single sheet highly wrinkled functionalized graphene

4 STM Images of FGS & HOPG K. N. Kudin, B. Ozbas, H.C. Schniepp, R.K. Prud homme, IAA, R. Car, Nano Lett. 8 (2008)

5 Functionalized Graphene Sheets FGS (C/O=1.85) without vacancy defect Unit cell FGS (C/O=1.64) with vacancy defect Unit cell C. Zhang, 2013 FGS: functionalized graphene sheet Large (>2µm diameter) polycyclic hydrocarbon Commercial production of single sheets (Vorbeck Materials, Jessup, MD) Sheet wrinkling inhibits restacking, maintains surface area Lattice defects Oxygen-decorated carbon vacancies Topological defects Oxygen-containing groups Epoxides, hydroxides, carboxyls

6 Oxygen-decorated vacancy Catalyzed NM Decomposition J. L. Sanbourin et al., submitted (2013) Catalytic role of FGS essential to transform nitromethane into more reactive intermediates Once formed, reactions continue within the fluid Fast decomposition: After ~14 ps, complete transformation into different species Main combustion products are H 2 O, CO 2, and N 2 Protonation, deprotonation and oxidation reactions promoted by oxygen groups on FGS at carbon vacancies

7 Tetrazine Decomposition A. Bhattacharya, J. Chem. Phys N N + 2RCN Low C, H content Good oxygen balance N-N increases heat of formation N N produced N-O enhances aromaticity, reduces sensitivity N N N +

8 Energetic Scaffolding Tetrazine bridge FGS Chemical modification of FGSs Planar and edge chemistries for attaching dispersants or binders Joining of FGSs for porous structures Spacers Long chain bridging molecules In collaboration with ENS Cachan (France) FGS Fabien Miomandre and Pierre Audebert, École Normale Supérieure de Cachan, France

9 Synthesis of Modified Tetrazines Fabien Miomandre and Pierre Audebert, École Normale Supérieure de Cachan, France A Dichloro-s-tetrazine (TzCl 2 ) B C HO OH + N N Cl Cl N N CH 2 Cl 2 2,4,6-collidine N N Cl O N N D O N N N N Cl

10 Pure tetrazines Tetrazines and Tz-FGS Tetrazines attached to FGS (Tz-FGS) JL4 C JL25: JL4 attached to FGS JL40 B JL24: JL40 attached to FGS JL41 JL43: JL41 attached to FGS JL37 D JL38: JL37 bridging 2 FGSs

11 Tetrazine Electrochemistry A π bond: resonance effect, e - donating Current A 60 6,0x10 3,0x10-7 0,0-3,0x Cl-Tz-Cl Cl-Tz-O-(CH 2 ) 4 -O-Tz-Cl Adam-CH 2 -O-Tz-Cl CH 3 -(CH 2 ) 3 -O-Tz-Cl cathodic σ bond: inductive effect, e - withdrawing For TzCl 2, inductive effect is much stronger than the resonance effect, making tetrazine ring electron deficient and redox peaks more positive B C -6,0x ,0x10-7 anodic -1,5-1,0-0,5 0,0 0,5 1,0 1,5 Potential V D Inductive effect from electron-donating groups: tetrazine ring becomes electron rich compared to ring in TzCl 2

12 Dichlorotetrazine and FGS A A Current 2,0x10-7 FGS 2 1,0x10-7 0,0 TzCl 2 Cl-Tz-O-Graphene TzCl 2 does not bind to FGS Confirmed by FTIR and thermal analysis TzCl 2 can react with solvent, catalyst Ab-initio model shows -1,0x10-7 TzCl 2 physisorption on FGS energetically -2,0x10-7 favored over chemisorption -1,5 15-1,0 10-0, ,0 05 0,5 10 1,0 15 1,5 Potential V

13 Tetrazines Bound to FGS B C Current A 3,0x10-6 FSG 2 CH 3 -(CH 2 ) 3 -O-Tz-Cl 2,0x10-6 1,0x10-6 0,0-1,0x10 10x ,0x ,0x10-6 Graphene-O-Tz-O-(CH ) -CH ,5 15-1,0 10-0, ,0 05 0,5 10 1,0 15 1,5 Potential V Current A 1,5x10-6 FGS 2 1,0x10-6 Adam-CH 2 -O-Tz-Cl Adam-CH 2 -O-Tz-O-Graphene O 5,0x10-7 0,0-5,0x ,0x ,5x ,5 15-1,0 10-0, ,0 05 0,5 10 1,0 15 1,5 Potential V Binding visible as shift in redox peaks for FGS and tetrazine Redox peaks of tetrazines shift to negative after grafting g (FGS acts as e - donating ggroup) Redox peaks of FGSs shift to positive after grafting (tetrazine acts as e - withdrawing group)

14 Abs Infrared Spectra of Pure Tetrazines C-H stretch JL 40 C-N stretch B JL 41 Abs Abs JL 4 C Abs JL 37 D Wavenumbers (cm -1 ) Strong C-N (aromatic) stretch between cm -1 C-H stretch from substituent groups ( cm -1 ) Ether bridge between substituent and tetrazine ring ~1200 cm -1

15 FGSs Bridged by Tetrazine D Current A 3,0x10-6 FGS 2 Cl Tz O (CH ) OTzCl Cl-Tz-O-(CH 2,0x ) 4 -O-Tz-Cl Graphene-O-Tz-O-(CH 2 ) 4 -O-Tz-O-Graphene 1,0x ,0-1,0x ,0x ,0x ,0x ,5-1,0-0,5 0,0 0,5 1,0 1,5 Potential V Redox peaks of JL 37, FGS shift as with other Tz-FGS products Shifts in redox peaks roughly equivalent for all Tz-FGS products, regardless of type of tetrazine grafted onto FGS Indicates similar bonding behavior (e.g., proximity of tetrazine ring to FGS through bridging g ether)

16 Abs JL 24 Infrared of Tetrazines on FGS C-N stretch C=O on FGS B Abs JL 43 Abs JL 25 C-H stretch C Abs JL 38 D Wavenumbers (cm -1 ) Tetrazine association with FGS indicated by C-H ( cm -1 ) and C-N (~1600 cm -1 ) stretching frequencies not seen on native FGS Ether bridge masked by multiple absorption bands in cm -1 region C-H and C-N bands disappear after heating Tz-FGS to high temperature (>400 C)

17 Modeling Tetrazine Binding to FGS Optimized Structures for FGS 2 and Dichloro-s-Tetrazine s d OH-N = 1.77 Å d OH-C = 2.44 Å FGS 2 mixed with TzCl 2 TzCl 2 covalently bound to FGS 2 vibrational mode corresponding to 3047 cm -1

18 Energy Difference: Products and Reactants Unit cell Å 3 ; Cubic cell Å 3 with MP correction E (Ry) - PBE E (Ry) - PBE-vdW E (ev) - vdw Dichloride-Tz (~6 Å) FGS FGS 2 - dichloride-tz (physi) FGS 2 - dichloride-tz (chemi) HCl FGS 2 + dichloro-tz FGS 2 - dichloro-tz (physisorbed) ΔE PBE = ev, ΔE PBE-vdW = ev FGS 2 - dichloro-tz (physi) FGS 2 1-oxy, 4-chloro-Tz (chemisorbed) + HCl ΔE PBE = ev, ΔE PBE-vdW = ev Covalent bond energetically unfavorable!

19 Optimized Structures for JL40 and JL24 JL40 JL24 B d OH-N = 1.72 Å d OH-C = 2.83 Å FGS 2 mixed with butoxy-tz (JL40) Butoxy-Tz (JL40) covalently bound to FGS 2 Vibrational mode corresponding to 2969 cm-1

20 Energy Difference: Products and Reactants Unit cell Å 3 ; Cubic cell Å 3 with MP correction E (Ry) - PBE E (Ry) - PBE-vdW E (ev) - vdw butoxy-tz (~10 Å) FGS FGS 2 - butoxy-tz (physi) FGS 2 - butoxy-tz (chemi) HCl FGS 2 + Butoxy-Tz FGS 2 - butane-tz (physi) ΔE PBE = ev, ΔE PBE-vdW = ev FGS 2 - Butoxy-Tz (physi) FGS 2 1-oxo, 4-butoxy-Tz (chemi) + HCl ΔE PBE = ev, ΔE PBE-vdW = ev Covalent bond energetically favorable! 20

21 Dichlorotetrazine and JL 40 Under N 2 TGA DSC mass (%) Change in Melting Vaporization Dichlorotetrazine B JL40 Hea at lost or ga ained (mw/m mg) Sublimation Temperature ( C) Under slow thermal ramp (10 C/min) dichlorotetrazine sublimes but JL 40 melts JL 40 vaporizes and does not decompose under experimental heating conditions

22 JL 40 and JL 24 Under N 2 TGA DSC mass (%) Change in Vaporization JL40 B JL24: JL40 on FGS Hea at lost or ga ained (mw/m mg) Melting Temperature ( C) Low molecular weight substituent sufficient to yield stable liquid phase Slow thermal ramp shows only desorption of tetrazine when associated with FGS

23 Energetics of Tetrazines and Tz-FGS S. Thynell In standard d thermal analysis, condense phase may vaporize during slow thermal ramp Confined Rapid Thermolysis (CRT)/FTIR Rapid heating rate 2000K/s to 1,000psig 50Hz sampling 2cm -1 resolution Sample allowed to decompose under isothermal conditions Very sensitive to decomposition occurring in condensed phases

24 Enhanced Decomposition of Tetrazines on FGS Tz Tz-FGS Tz S. Thynell Evolved gas analysis during CRT shows JL 37 and JL 40 decompose at 335 C Decomposition of tetrazine (JL 37) is more extensive when bound to FGS (JL 38) no tetrazine vapor apparent, higher amounts of decomposition products formed In comparison, dichlorotetrazine goes into vapor phase with no decomposition

25 T-Jump Time-of-Flight Mass Spec diameter Pt wire is coated with sample of interest. Wire is rapidly heated at 10 5 K/s within the extraction region of a linear TOF mass spectrometer. Time resolved spectra are acquired during a single reaction event. Electrical characteristics of the wire are monitored to determine wire temperature at any given time during heating. A data sampling rate of 10 khz was used. L. Zhou, et al., M.R. Zachariah, Rap. Commun. Mass Spec. (2009)

26 JL 37 and JL 38 Decomposition of pure tetrazine (JL 37) is delayed when attached to FGS (JL 38) Significant decomposition of JL 37 at 0.6 ms (597 K), delayed to 1.4 ms on FGS (840 K) No large mass fragments in JL 38: more complete decomposition of tetrazine

27 Dielectric Elastomers with Stiff Electrodes Voltage as a function of stretch (electrodes: 3 wt. % FGS22-SE; SE; elastomer: VHB, H2/H1=0.2) λ'= λ 5

28 Adaptive Materials (Nanocomposites) Z. Fang, et al., IAA Appl. Opt. 49 (2010)

29 Summary Developed synthesis methods to construct nanocomposite fuels using functionalized graphene sheets as (i) nucleation templates and stabilizer for energetic particles, polymeric nitrogen molecules, embedded nitrogen; and (ii) carbocatalysts Covalent attachment of tetrazines is confirmed by CV, FTIR, thermal analysis, and quantum mechanical modeling to understand the fundamental mechanisms of energetic functions. High surface area, hierarchically structured graphene-tetrazine networks will be developed for controlled energy release.