Thermal properties of phosphorylated nanodiamond reinforced polyimides

Recently, the preparation of nanodiamond–polymer composites has attracted the attention of materials scientists due to the unique properties of nanodiamonds. In this study, novel polyimide (PI)/phosphorylated nanodiamonds (PNDs) composites were prepared. PNDs were achieved from the reaction of methylphosphonic dichloride with nanodiamonds in dichloromethane. Precursor of polyimide, which is the poly(amic acid) (PAA), was successfully synthesized with 3,3′, 4,4′‐benzophenonetetracarboxylic dianhydride and 4,4′‐oxydianiline in the solution of N,N‐dimethylformamide. Different ratios of phosphorylated nanodiamond particles were added into PAA solution and four different nanocomposite films were prepared. The amount of PNDs in the composite films was varied from 0 wt% to 3 wt%. The structure, thermal and surface properties of polyimide films were characterized by scanning electron microscopy (SEM), ATR‐FTIR, thermogravimetric analysis (TGA), ultraviolet visible spectroscopy, and contact angle. SEM and FTIR results showed that the phosphorylated nanodiamond and PI/PNDs films were successfully prepared. Phosphorylated nanodiamonds were homogeneously dispersed in the polymer matrix and they displayed good compatibility. TGA results showed that the thermo‐oxidative stability of PI/PNDs films was increased with the increasing amount of phosphorylated nanodiamond. POLYM. COMPOS., 37:2285–2292, 2016. © 2015 Society of Plastics Engineers     

Effect of nanodiamond surface functionalization using oleylamine on the scratch behavior of polyacrylic/nanodiamond nanocomposite

Addition of hard particles such as nanodiamonds to polymers to improve their physical and mechanical properties is very common. However, nanodiamonds are usually hydrophilic so their tendency to form agglomerates in a polymeric matrix is quite strong. In this study, the effect of nanodiamond surface modification on its uniform dispersion in a polymeric matrix such as polyacrylic-base polymer clear coat was investigated. For this purpose, detonation nanodiamond (DND) with an average particle diameter of 4–6 nm was used. To improve dispersion of as-received DND (AR-DND) in the polymeric matrix, the surfaces of the particles were modified by heat treatment (oxidation) in air and followed by functionalization using oleylamine (OLA) as surfactant. So, nanocomposites with different contents of AR-DND, HT-DND and OLA treated HT- DND (OLA-HT-DND) particles were produced. Their characterizations were investigated by employing many analytical methods such as: Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermo-gravimetry analysis (TGA). Scratch resistance test and study of coating surfaces, using scanning tunneling microscopy (STM), were carried out on the polymeric nanocomposites. The results showed that the surface-functionalized nanodiamonds are highly dispersive and stable in the polymeric matrix. In addition, scratch resistance was increased with the addition of nanoparticles.     

Onion-like carbon deposition by plasma spraying of nanodiamonds

A deposit of carbon nanoparticles based on an onion-like structure was fabricated from detonation nanodiamond powders by a novel plasma spraying process, electromagnetically accelerated plasma spraying (EMAPS). EMAPS was able to transform nanodiamonds to onion-like structured carbon within 300 μs through a thermal graphitization process in which the temperature of the particles would be in the range of 2700-4500 K. Synthesized onion-like carbon nanoparticles were spherical or polyhedral. The G-band in the UV-Raman spectra of the produced deposits was found to be a superposition of a characteristic band of well-formed carbon onions at 1571 cm⁻¹ and the G-band of defective carbon onions at 1592 cm⁻¹. The availability of a plasma spraying process for developing solid lubricant coatings incorporating nanodiamond and onion-like carbon was demonstrated.     

Detonation of nanosized explosive: New mechanistic model for nanodiamond formation

While nanodiamonds are synthesized by detonation of microstructured explosives since 50 years ago, we developed a novel approach to synthesize these particles by using nanostructured explosives. This new synthesis method leads to novel results not only in the control of the size, but also in the understanding of the nanodiamond synthesis and the detonation mechanisms. The use of explosive particles with size down to 40 nm results in the formation of detonation nanodiamonds with a mean size of 2.8 nm. In the light of these experiments, a model based on the size of the material involved during the detonation process has been developed to explain the size of the obtained nanodiamond. According to hypotheses based on the number of the nanodiamond nucleation sites, the experimental results are in favor of a decrease in the size of the nanodiamonds formed when the size of the explosive particles used during detonation is decreased.     

Diamond nanoparticles in ethylene glycol lubrication on steel–steel high load contact

Nanodiamond dispersions in ethylene glycol were applied in order to improve the boundary lubrication in high power density contacts. A range of nanodiamond concentrations in ethylene glycol were studied by stainless steel vs. stainless steel contact by a pin-on-disc tribometer. As compared to pure ethylene glycol, friction coefficient decreased from 0.16 to 0.11 when maximum concentration (3.7 wt.% of nanodiamonds) and 100 N normal load were applied. A minimum wear for both the disc and counter ball was detected when nanodiamond concentration of 2.2 wt.% or 0.55 wt.% was used. The mechanism of nanodiamond lubrication was determined to be incorporation of nanodiamonds into the tribolayer formation.     

Dual reaction capacity of hydrogenated nanodiamond

High temperature hydrogen stream treatment of nanodiamond was shown to produce nanodiamond with bifunctional surface. OH- and different CH-groups were shown to be the main functional groups on the surface. In this article we proposed two main strategies for further chemical modification of hydrogenated nanodiamond. OH-groups were shown to react with different types of acylating agents: anhydrides and chloranhydrides. Chlorination of hydrogenated nanodiamond with molecular chlorine and its subsequent treatment with alkyllithium reagents resulted in formation of alkyl-nanodiamonds. Chlorination was shown to reduce the size of nanodiamonds aggregates. We have also applied suspension-state NMR-H1 spectroscopy to study suspensions of alkyl-nanodiamonds for the first time.     

Cool plasma functionalization of nano-crystalline diamond films

It was demonstrated that an atmospheric pressure dielectric barrier glow discharge system is a powerful tool for the surface functionalization of nano-crystalline diamond films. Diamond film functionalization was performed in minutes using plasma discharges generated with fluorine containing gases. The chemical bonds formed between reactive species generated in the plasma and diamond surface were confirmed by FTIR and XPS analysis. Following plasma treatment, XPS analysis revealed a high concentration of F on the diamond surface, nearly 50 atomic percent. FTIR analysis revealed the presence F-bands related to CF₃ (CF₂) stretching vibrations and symmetric and asymmetric CF₂ vibrations. It was concluded that atmospheric pressure dielectric barrier glow discharge is a highly effective means to fluorinate diamond surfaces within a modest time.     

Hyperbranched polyglycerol modified fluorescent nanodiamond for biomedical research

The aim of the present work was to functionalize fluorescent nanodiamond by covalent grafting with hyperbranched polyglycerol. Fluorescent nanodiamond, derived from high pressure high temperature micron-sized diamond, was oxidized and then thermally reacted with pure glycidol in the absence of catalyst. The results revealed that thermal polymerization of glycidol was notably faster on the nanodiamond surface as a result of a surface initiation of the isothermal ring opening polymerization. Interestingly, the aqueous dispersion of the resulting nanoparticles appeared stable at high ionic strength. Furthermore, the fluorescent nanodiamond grafted with hyperbranched polyglycerol displayed several hydroxyl end-groups which could be further derivatized by carboxylation or carbamatization and subsequently conjugated with protein linked via an amide bound. Notably, nanodiamonds retain their unique fluorescent characteristics. This work suggests that fluorescent nanodiamond coated with hyperbranched glycidol could be promising in biomedical research where aqueous dispersion of fluorescent nanoparticles stable in physiological medium is in high demand to label, track and quantify biomolecules.     

Cost-effective route to nanodiamonds from low-rank coal and their fluorescent & dielectric characteristics

The synthesis of nanodiamonds from abundant and inexpensive precursors has recently piqued the curiosity of researchers. It has the potential to significantly reduce the cost of nanodiamonds and open up a plethora of new applications. In this work, fluorescent nanodiamonds with smaller particle sizes with rich surface functionality are synthesized from low-grade coal lignite by employing a facile acidic oxidation and ultrasonication approach. The extracted nanodiamond particles are hydrophilic and display high excitation-dependent fluorescence in the aqueous medium. The excitation-dependent fluorescence can be ascribed to the collaboration and competition of the OH and COOH functional groups. The as-synthesized nanodiamonds also show good dielectric permittivity and ac conductivity over a wide frequency range at room temperature. The present research opens up the possibility of mass production of nanodiamonds on the industrial scale from a low-cost precursor.     

Specific Features of Synthesis of Detonation Nanodiamonds

It is demonstrated that the Chapman-Jouguet parameters for high explosives used in nanodiamond synthesis are located in the region of liquid nanocarbon; therefore, the chemical reaction zone of the detonation wave involves formation of carbon nanodroplets, which are later crystallized into nanodiamonds on the segment of the isentrope of expansion of detonation products, passing through the region of stability of nanodiamonds in the pressure range of 16.5–10 GPa and the temperature range of 3400–2900 K. Soot in the resultant mixture is the product of amorphization of nanodroplets rather than graphitization of ultrafine diamonds. The influence of detonation conditions of high-explosive charges in an explosive chamber on nanodiamond synthesis is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 104–116, September–October, 2005.     

Electronic properties of dehydrogenated nanodiamonds: A first-principles study

First-principles calculations using quantum-mechanical density functional theory (DFT) are carried out to study the geometric structure and electronic properties of dehydrogenated nanodiamonds with diameters varying from 0.8 nm to 1.6 nm. The results show that the electronic properties of dehydrogenated nanodiamond are quite different from those of bulk diamond or hydrogenated nanodiamond. Surface atoms play an important role in the electronic structure, especially the states near the Fermi level, for dehydrogenated nanodiamond. In addition, it has been revealed that the size-dependent feature in the electronic properties for dehydrogenated diamonds is also contributed by the surface effect, in addition to the quantum confinement effect.     

Survey study of mercury determination in detonation nanodiamonds by pyrolysis flameless atomic absorption spectroscopy

A set of 20 commercially available nanodiamond samples of eight manufacturers of various countries, which are most frequently used in basic and applied studies, was analyzed for the concentration of Hg. Conditions of mercury determination by flameless atomic absorption spectroscopy with thermal sample decomposition (pyrolysis) at 800 °C were proposed and confirmed by wavelength-dispersive X-ray fluorescence analysis. It was found that nanodiamonds have a significant diversity of amounts of mercury, from 20 μg/kg to higher than 0.7 g/kg. Thus, the need to control Hg impurity in nanodiamonds, especially for biological and medical research, was demonstrated. The precision of flameless pyrolysis atomic absorption determination of mercury in nanodiamonds is discussed.     

Modeling the thermostability of surface functionalisation by oxygen, hydroxyl, and water on nanodiamonds

Understanding nanodiamond functionalisation is of great importance for biological and medical applications. Here we examine the stabilities of oxygen, hydroxyl, and water functionalisation of the nanodiamonds using the self-consistent charge density functional tight-binding simulations. We find that the oxygen and hydroxyl termination are thermodynamically favourable and form strong C–O covalent bonds on the nanodiamond surface in an O2 and H2 gas reservoir, which confirms previous experiments. Yet, the thermodynamic stabilities of oxygen and hydroxyl functionalisation decrease dramatically in a water vapour reservoir. In contrast, H2O molecules are found to be physically adsorbed on the nanodiamond surface, and forced chemical adsorption results in decomposition of H2O. Moreover, the functionalisation efficiency is found to be facet dependent. The oxygen functionalisation prefers the {100} facets as opposed to alternative facets in an O2 and H2 gas reservoir. The hydroxyl functionalisation favors the {111} surfaces in an O2 and H2 reservoir and the {100} facets in a water vapour reservoir, respectively. This facet selectivity is found to be largely dependent upon the environmental temperature, chemical reservoir, and morphology of the nanodiamonds.     

First-principles density-functional investigation on the electronic properties and field emission of a hydrogenated nanodiamond

First-principles calculations using quantum-mechanical density functional theory (DFT) are carried out to investigate the geometrical structure and electronic properties for hydrogen terminated nanometer-sized diamonds. The results reveal that the size dependent feature in the electronic structures for nanodiamonds is different from that of Si clusters. The field emission properties for nanodiamonds are also explored, and it is found that under applied electric field Mulliken charges redistribute and accumulate on the emission side. Furthermore, the emission currents from the occupied orbitals for nanodiamond are calculated and it is revealed that the largest emission current comes from the third highest occupied molecular orbital.     

Diamond nanoseeding on silicon: Stability under H2 MPCVD exposures and early stages of growth

Detonation nanodiamond dispersed on silicon surfaces underwent different H₂ MPCVD exposures. The induced changes at the surface have been characterized in situ by XPS and XEELS. Then, a short CH₄/H₂ growth step was applied. This sequential study revealed an excellent stability of detonation nanodiamond. The sp³ etching rate is insufficient to remove nanodiamond even under intense H₂ plasma. The H₂ exposure could be successfully used to remove C–C sp² carbon without altering sp³ seeds. Moreover, the formation of silicon carbide observed after the hydrogen treatment is thought to be helpful to enhance the adhesion of nanodiamond particles on the substrate.     

Deposition of detonation nanodiamonds by Langmuir–Blodgett technique

Langmuir–Blodgett technique, which classically allows preparing monomolecular films, was here used to deposit a film of detonation nanodiamond particles.We proceeded to the functionalization of the nanodiamond (nD) particles so as to obtain hydrophobic nanodiamonds. Cetyltrimethylammonium chloride (C₁₉H₄₂ClN) (CTAC) was used for this purpose in order to form an ionic complex ND–COO^?(NH₃)⁺–R with the functional groups of the nanodiamonds.Compressions with various strengths (10 to 30 mN/m) were performed on the Langmuir–Blodgett device in order to prepare different types of deposits on mica substrates. Atomic Force Microscopy was used to characterize these deposits. It was shown that compressions with low intensity result in discontinuous distributions of the particles on the surface. Conversely, very dense and continuous deposits were observed for higher compression strengths. By optimizing the nD/CTAC ratio in the suspension, a very regular deposit with a monoparticle height was obtained.     

Nanodiamond synthesis by pulsed laser ablation in liquids

Pulsed laser ablation in liquids (PLAL) has become an attractive method for the synthesis of nanodiamond. This work deals with the growth kinetics study of structures of nano-diamonds embedded in sp² carbon synthetized by this method. The plasma created by the laser pulse has been monitored by time resolved spectroscopy to analyze the evolution of the plume and therefore the transient species created. Typical C₂ vibrational bands appear, as well as a continuous spectrum due to various phenomena. The study of both the background and the vibrational features gives information on the reaction kinetics and on the plasma density. The presence of nanodiamonds has been confirmed by Raman spectroscopy as well as TEM analysis.     

Mechanical and electronic properties of ultrathin nanodiamonds under uniaxial compressions

Mechanical and electronic properties of ultrathin hydrogenated nanodiamonds (with diameters from 0.71 nm to 1.4 nm) under uniaxial compression have been investigated by means of density functional theory calculations. The computed Young's moduli of nanodiamonds are lower than the bulk value and increase with size, which can be fitted to an empirical function of diameter. Similar to the bulk diamond, the HOMO–LUMO gaps of nanodiamond reduces under uniaxial strain, implying tunable electronic properties via mechanical deformations.     

Pressure induced changes in fractal structure of detonation nanodiamond powder by small-angle neutron scattering

The results of the experiments on small-angle neutron scattering from the industrial detonation nanodiamond powder under a pressure in the range of up to 1000 MPa are reported. It is shown that at a scale of 10–100 nm the scattering is determined by the fractal pore structure within aggregates of nanodiamonds. Its fractal dimension monotonously decreases with pressure from 1.8 to 1.2, which indicates the recombination of pores as a result of mobility of nanodiamonds in the powder under pressure. The mean pore size under the highest pressure (6 nm) is close to the characteristic size of nanodiamonds in the sample (5 nm) found from the width of X-ray diffraction peaks. The difference can be explained by the existence of a non-diamond carbon shell around diamond crystallites.     

Surface planarization of zirconia ceramic achieved by polyacrylamide grafted nanodiamond composite abrasives through chemical mechanical polishing

Zirconia ceramics are the promising materials for cell phone backplanes in the 5G era, and smoother surfaces and higher removal efficiency are sought after for their precision machining. Although nanodiamond abrasives have high polishing rates, it is easy to bring mechanical scratches and pits on the ceramic surface because of their high hardness, resulting in degradation of the surface quality of the finished workpiece. Therefore, polyacrylamide grafted nanodiamond particles were prepared by solution polymerization method for polishing ceramic wafers. As confirmed by Fourier transform infrared spectroscopy (FTIR), the polyacrylamide has been grafted on the nanodiamond surface. According to the scanning electron microscopy (SEM) and particle size distribution, the composite abrasives have better dispersion than pure nanodiamond abrasives. The results of chemical mechanical polishing (CMP) experiments showed that the composite abrasives could reduce the average surface roughness (Sa, arithmetic mean height) of zirconia ceramic from 28.31 nm to 2.68 nm (scanning area is 500 μm × 500 μm), and the polishing rate remained high compared to pure nanodiamond abrasives, showing superior CMP performance. X-ray photoelectron spectroscopy (XPS) demonstrated that solid-phase chemical reactions occurred during the polishing process to form ZrSiO₄. Meanwhile, contact-wear model combined with contact angle testing indicates that the introduction of polyacrylamide increases the contact area of the nanodiamond on the zirconia wafer surface, thereby significantly enhanced the mechanical effect.