Cation-directed orientation of amines in ternary graphite intercalation compounds

1,2-Diaminopropane (1,2-DAP) provides an unusual example of an organic co-intercalate where graphite intercalation compounds (GICs) show intra-gallery orientation dependant on the identity of the alkali metal cation intercalate (Li⁺, Na⁺, or K⁺). The GIC gallery heights, K(1,2-DAP)_yC_x = 0.697 nm and Li(1,2-DAP)_yC_x = 0.782 nm, indicate 1,2-DAP long axis orientations that are parallel or perpendicular to the graphene sheets, respectively.     

Production of natural graphite particles with high electrical conductivity by grinding in alcoholic vapors

Natural graphite particles with a high crystallinity, which were sieved to obtain particles less than 63 μm, were ground with a ball mill under a dry atmosphere and various alcoholic vapors such as i-C₃H₈OH, n-C₃H₈OH, C₂H₅OH, and CH₃OH. The size and flakiness of the ground products and the electrical conductivity of the films made from the ground products were experimentally examined. Grinding the particles under alcoholic vapors slowly reduced the particle size and was similar to grinding in dry air, but grinding in alcoholic vapors produced flakier products. The graphite films, which were composed of flakier particles and were ground in alcoholic vapor, displayed higher electrical conductivities than the feed graphite particles. The products ground in C₂H₅OH, i-C₃H₇O and n-C₃H₇OH vapors had 50% or less of the specific resistance of the feed particles.     

Production of finely ground natural graphite particles with high electrical conductivity by controlling the grinding atmosphere

Natural graphite particles with high crystallinity sieved to obtain a particle size range of under 63 μm were ground with a ball mill, under various well-controlled grinding atmospheres such as N₂, O₂, He, H₂, and vacuum. The ratio, X_dif50/X_st50, i.e. between the 50 wt.% Stokes diameter and the 50 wt.% laser diffraction diameter, of the ground particles, was used as an index of the flakiness of the particles. The specific resistance of films composed of the ground graphite particles was systematically measured. The rate of reduction in the size of the particles by grinding was slow under an O₂-rich atmosphere such as 100% O₂ and dry air. On the other hand, it was relatively fast in vacuum, or under an N₂ or He atmosphere, and a gas mixture of 99% N₂ and 1% O₂. The rate of size reduction by grinding under a H₂ atmosphere was intermediate. In our experimental conditions, the flakiness of the ground particles increased with the decrease in the particles’ sizes. The electrical conductivity of the ground particles, however, tended to decrease with the decrease in their sizes. Under the condition that the Stokes diameter of the ground particles remains constant, the electrical conductivity of films made from the ground particles increases with the increase in the flakiness of the particles. It was finally determined from our systematic grinding experiments that small flaky particles, which had a size, X_st of ∼1 μm, with a high electrical conductivity can be produced by grinding in a gas mixture of 99% N₂ and 1% O₂. In this case, the flaky shape of the ground particles was visually confirmed by scanning electron microscopy.     

Scalable production of graphene sheets by mechanical delamination

Mono- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a wet grinding process under mild milling conditions. The shear forces in the milling chamber lead to a continuous delamination of ultrathin graphene flakes which are dispersed in a liquid medium. To avoid agglomeration of the exfoliated flakes the anionic surfactant sodium dodecyl sulfate was used. By adjusting the process parameters in a way to overcome the weak interlayer forces between the sheets without breaking them leads to the fabrication of thin flakes with high aspect ratios. The presented scalable process allows a high-yield and low-cost production of free-standing graphene sheets for various applications.     

A simple model of the a-axis conductivity in graphite intercalation compounds

A simple calculation, based on the effective mass approximation and assuming a purely two-dimensional Fermi surface, is performed to estimate the dependence of a-axis conductivity σ_a upon intercalant concentration X in the lamellar compounds of graphite. The predicted behavior $\text{σ}{}_{\mathrm{a}}\text{~ X}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ is in approximate agreement with experiment only for the case of ICI, which is attributed to the unusually large layer spacing, hence weak interaction between layers, in this compound.     

Preparation,structure and electrical conductivity of graphite intercalation compound with titanium fluoride

The graphite intercalation compound (GIC) of titanium fluoride has been prepared in a fluorine atmosphere. The GICs prepared from natural graphite and pitch-based carbon fiber were mostly stage-2 compounds with repeat distance 11.28–11.59 Å and composition C_11–15TiF_4.5–6.2. The ESCA spectrum indicates that intercalated TiF₆²⁻ anions are mainly in a bridged state. The slight decrease in the repeat distance with increasing fluorine pressure is ascribed to the nestling of TiF₆²⁻ anions in benzene rings of carbon layers due to the increase in nonbridging TiF₆²⁻ anion. X-ray powder diffraction data indicate the high regularity in the orientation of intercalated species between carbon layers. The highest electrical conductivity was 2.4 × 10⁵ Scm⁻¹, which is 13 times higher than that of pristine HOPG.     

Restoring electrical conductivity of dielectrophoretically assembled graphite oxide sheets by thermal and chemical reduction techniques

Thin layers of graphite oxide sheets were dispersed in dimethylformamide and dielectrophoretically assembled onto predefined and opposing metal electrodes. The dielectrophoretic method resulted in the deposition of multiple layers of graphite oxide. After drying, the deposits were then reduced by thermal or chemical methods. Raman spectroscopy and electrical transport measurements revealed that the thermal reduction technique was more effective in restoring electrical conductivity than the chemical reduction method.     

Near perfect thin film flexible broadband optical absorber with high thermal/electrical conductivity

Flexible ultra-black absorber with high thermal/electrical conductivity finds huge applications in the field of stray light attenuation, solar collectors, flexible electronics, and electronic thermal management systems. In this work, we report the fabrication of ultrablack absorber consists of vertically aligned carbon nanotubes (VACNT) in Polydimethylsiloxane (PDMS) having an absorption capacity of more than 98% in UV–Vis wavelength and more than 94% in NIR wavelength range. It is observed that the PDMS-VACNT composite shows ultra-high absorption capacity due to enhanced impedance matching and multiple scattering. In addition to this, the PDMS-VACNT composite shows an emissivity of 0.94 along with a 118% increase in thermal conductivity. Moreover, with the infiltration of VACNT in PDMS, the sheet resistance decrease drastically to 0.08 KΩ/sq, which signify the possible use of ultrablack absorber in electronic skin and flexible sensors etc. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48855.     

Enhanced mechanical and electrical properties of polyimide film by graphene sheets via in situ polymerization

In this study, polyimide/graphene nanocomposite films which exhibited significant enhancements in mechanical properties and electrical conductivity were successfully fabricated. Graphene oxide (GO) synthesized by Hummer’s method was chemically modified with ethyl isocyanate to give ethyl isocyanate-treated graphene oxide (iGO), which is readily dispersed in N,N′-dimethylformamide (DMF). The iGO dispersion in DMF was then used as media for synthesis of polyimide/functionalized graphene composites (PI/FGS) by an in situ polymerization approach. It was shown that addition of only 0.38 wt% of FGS, Young’s modulus of the PI/FGS composite film was dramatically increased from 1.8 GPa to 2.3 GPa, which is approximately 30% of improvement compared to that of pure PI film, and the corresponding tensile strength was increased from 122 MPa to 131 MPa. In addition, the electrical conductivity of the PI/FGS with this graphene content was increased by more than eight orders of magnitude to 1.7 × 10⁻⁵ S m⁻¹.     

A comparative structural study of ternary graphite intercalation compounds containing alkali metals and linear or branched amines

New donor-type ternary graphite intercalation compounds (GICs) containing alkali metals and branched amines are prepared by direct reaction of graphite with the alkali metal and amine. The new GICs include M(iC3)_0.4C_15–18 (M = Li, Na; iC3 = iso-propylamine; d_i = 0.76 nm) with a monolayer intercalate arrangement; and Na(sC4)_1.6C₁₈ (sC4 = sec-butylamine; d_i = 1.34 nm) and Na(iC4)_2.0C₂₈ (iC4 = iso-butylamine; d_i = 1.28 nm) with bilayer arrangements. Li-sC4-GIC and K-iC3-GIC are not formed using this reaction chemistry. M-iC3-GICs show galleries expanded by 0.06 nm more than that for M(nC3)_0.7–0.8C₁₆ (M = Li, Na; nC3 = n-propylamine). Unlike the case of rigid-sheet hosts where branched amines intercalate at a lower rate and with lower amine content, M-sC4-GICs and M-iC4-GICs readily form intercalate bilayers.     

Mechanism of the anionic polymerization of lactones,initiated by intercalation graphite compounds

Summary The anionic polymerization of -propiolactone (PL)oxethane-2-one, pivalolactone (PVL) — 3,3-dimethyloxethane-2-one and -caprolactone (CL) — oxepane-2-one, initiated by binary and ternary intercalation compounds (IC) of lithium and potassium in graphite is investigated. The polymerization is carried out in bulk or in xylene. It is established that the lactones penetrate in IC and polymerize in their interlayer spacings. The polymerization causes a delamination of IC. High polymers of the lactones can be obtained by the action of some IC investigated.     

Pentadecane functionalized graphite oxide sheets as a tool for the preparation of electrical conductive polyethylene/graphite oxide composites

Covalent functionalization of pentadecane-decorated thermally reduced graphite oxide (GO) sheets has been studied as a tool for the preparation of polyethylene/GO composites exhibiting rheological and electrical percolation thresholds. It was accomplished through pentadecane based radical addition onto unsaturated bonds located on the GO sheets' surface using dicumyl peroxide as hydrogen abstractor. This chemical functionalization influences the affinity of the formed pentadecane grafted GO sheets for various solvents. Then, the compounding of the composites pentadecane grafted GO/PE was performed at a processing temperature of 140 °C with 25, 20, 15, 10, 8 and 5 wt% loadings. Rheological and electrical percolation thresholds were found between 10 and 15 wt% for polyethylene/pentadecane functionalized graphene oxide composites while the composite graphite/PE at the same loading percentage did not reach any percolation threshold.     

Effect of polypyrrole film on the stability and electrochemical activity of fluoride based graphite intercalation compounds in HF media

Fluoride intercalation/deintercalation cycles on commercially available high purity graphite electrodes leads to powder formation and electrode damage. Formation of polypyrrole films of optimum thickness by potential cycling on the graphite surface before fluoride intercalation leads to good mechanical stability to the electrode during intercalation/deintercalation cycles. The intercalation potential shifts by 200 mV in the positive direction. The intercalation and deintercalation charges (Q _a, Q _c) also decrease slightly. However the charge recovery ratio (Q _c/Q _a) improves significantly. Since the polypyrrole layer is compact on the graphite surface, the present study indicates that the film offers mechanical stability to the graphite film without affecting the electronic conductivity of the surface. F^– ion transport through the film also occurs with a small overvoltage.     

Structural investigations of graphite intercalation compounds of antimony chloride fluorides by Moessbauer spectroscopy

Natural graphite flakes were intercalated by SbCl₅, SbCl₄F and SbCl₂F₃ at T ≤ 125°C for a reaction time of t ≤ 2 hours. The ¹²¹Sb Moessbauer spectra of the stage 2 intercalation compounds show only one intense line in the Sb(+ 5) region. The spectra can be fitted both in terms of two inequivalent Sb(+ 5) sites and of a single Sb(+ 5) site. The isomer shifts 6 increase by replacing Cl by F in the intercalates as well as by intercalation of the halides in the graphite lattice. The isomer shifts of the intercalation compounds are attributed to polymeric species of the type (mSbX₅ · SbX₆)⁻. Because the spectra provide no evidence for Sb(+ 3), a significant oxidation of graphite is ruled out. Intercalation compounds heated for a long time at 150°C were found to exhibit a dramatically high concentration of Sb(+ 3) which is interpreted as the result of a thermal decomposition of the pentahalides.     

The synthesis and electrical conductivity of a polyacrylate/graphite hydrogel

A polyacrylate/graphite composite was synthesized by aqueous solution polymerization. Based on the electrical conductivity of graphite and the water absorbency of polyacrylate, a novel conductive hydrogel with a conductivity of 7.3 mS m⁻¹ was prepared. The influence of crosslinker, initiator, monomer, neutralization degree, graphite, water absorbency and temperature on the electrical conductivity of the hydrogel was investigated. An appended network structure model of the polyacrylate/graphite conductive hydrogel is proposed.     

Structure and electrical properties of grafted polypropylene/graphite nanocomposites prepared by solution intercalation

A novel process was developed to prepare electrically conducting maleic anhydride grafted polypropylene (gPP)/expanded graphite (EG) nanocomposites by solution intercalation. The conducting percolation threshold at room temperature (Φ_c) of the nanocomposites was 0.67 vol %, much lower than that of the conventional conducting composites prepared by melt mixing (Φ_c = 2.96 vol %). When the EG content was 3.90 vol %, the electrical conductivity (σ) of the former reached 2.49 × 10^?3 S/cm, whereas the σ of the latter was only 6.85 × 10^?9 S/cm. The TEM, SEM, and optical microscopy observations confirmed that the significant decrease of Φ_c and the striking increase of σ might be attributable to the formation of an EG/gPP conducting multiple network in the nanocomposites, involving the network composed of particles with a large surface‐to‐volume ratio and several hundred micrometers in size, and the networks composed of the boards or sheets of graphite with high width‐to‐thickness ratio and particles of fine microscale or nanoscale sizes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1864–1869, 2003