Chemically modified nanomaterials as lubricant additive: time stability, friction, and wear

This work reviews the results on the temporal stability of nanodispersions containing chemically modified nanoadditives: carbon-based nanomaterials, metals, metal oxides, metal sulfides, nanocomposites, among others. Morphology, size, coating type and concentration of the NPs as well as the viscosity of the base oil are the main characteristics that affect stability. Coated spherical NPs with mean diameter lower than 20 nm are the most common among those which led to nanolubricants with stabilities longer than two months. The tribological results of the nanolubricants with stabilities higher than one month are also reviewed. Regardless the base oil, chemically modified nanoparticles reduced wear more than friction, reaching reductions of friction up to 75% and wear volume up to 99%. As for the tribological mechanisms involving chemically modified nanoparticles, the formation of adsorbed or tribochemical reaction films on worn surfaces were reported more oftenThis work is supported by MCIN/AEI/10.13039/501100011033 and by the European Regional Development Fund (ERDF, FEDER in Spanish) through the ENE2017-86425-C2-2-R and the PID2020-112846RB-C22 projects as well as by Xunta de Galicia (ED431C 2020/10). JMLDR acknowledges the grant of the Margarita Salas program, funded by MCIN/AEI/10.13039/501100011033 and “NextGenerationEU/PRTR”S

Design and Characterization of Lubricants Based on Functionalized Nanoparticles

The main objective of this PhD thesis is to design and characterize efficient nanolubricants based on three polyalphaolefins (PAOs) and nanoparticles (NPs) of metal oxides or ceramics coated with organic acids for wind turbine gearboxes and electric transmissions of electric vehicles. First, preliminary tests and an in-depth literature survey on the time stability and tribological behavior of nanodispersions containing chemically modified nanoadditives were performed. Then, the thermophysical and tribological properties of PAO nanolubricants containing coated NPs (ZnO-OA, TiO2-OA, or SiO2-SA) were evaluated; in addition, possible tribological mechanisms were analyzed by confocal Raman microscopy. All the coated NPs studied improve the tribological behavior of their base oil, being the best the SiO2-SA NPs

Effect of HDI-Modified GO on the Thermoelectric Performance of Poly(3,4-ethylenedioxythiophene):Poly(Styrenesulfonate) Nanocomposite Films

Composite films based on conducting polymers and carbon nanomaterials have attracted much attention for applications in various devices, such as chemical sensors, light-emitting diodes (LEDs), organic solar cells (OSCs), among others. Graphene oxide (GO) is an ideal filler for polymeric matrices due to its unique properties. However, GO needs to be functionalized to improve its solubility in common solvents and enable the processing by low-cost solution deposition methods. In this work, hexamethylene diisocyanate (HDI)-modified GO and its nanocomposites with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were developed, and their morphology, thermal, electrical, thermoelectrical and mechanical performance were characterized. The influence of the HDI functionalization degree and concentration on the nanocomposite properties were assessed. The HDI-GO increased the crystallinity, lamella stacking and interchain coupling of PEDOT:PSS chains. A strong improvement in electrical conductivity, thermal stability, Young's modulus and tensile strength was found, showing an optimum combination at 2 wt% loading. Drop and spin casting techniques were applied onto different substrates, and the results from deposition tests were analyzed by atomic force microscopy (AFM) and UV-vis spectroscopy. A number of parameters influencing the depositions process, namely solvent nature, sonication conditions and ozone plasma treatment, have been explored. This study paves the way for further research on conducting polymer/modified GO nanocomposites to optimize their composition and properties (i.e., transparency) for use in devices such as OSCs

Antistatic polymer materials

ABSTRACT: Introduction. In connection with the growing demand for living and working conditions in civil and industrial construction, there is an increasing need for high-quality building materials with the required set of performance properties. Polymer reinforced composite materials are promising materials in the construction industry due to their high strength, durability, reliability and economy. Polymers such as polyvinyl chloride, polyurethanes, polyacrylates, epoxy resins, polypropylene are used in construction for the manufacture of decorative elements, self-leveling floors, coatings for appliances and equipment. However, the use of polymeric materials creates risks of electric shock due to the generation of static charge. The use of electrically conductive nanomaterials as fillers makes it possible to reduce the resistivity of polymeric materials and slow down the flow of electric charges. Main part. This review article presents the benefits and drawbacks of antistatic additives for polymer materials used in industry and in the construction industry. Conclusion. An analysis of the literature has shown that over the past seven years, the largest number of relevant papers has been devoted to carbon materials as antistatic additives (8 articles), metal and metal oxide nanoparticles (7 articles), ionic liquids (7 articles), and polyaniline (7 articles). The most studied characteristics of antistatic polymer materials are the specific surface RS and volume RV resistances. According to the reviewed articles, metal and metal oxide nanoparticles are the most suitable antistatic additives to polymeric materials, since they are well dispersed in the polymer matrix. However, further research is needed to eliminate the negative effect of nanoparticles on the mechanical properties of polymeric material

Preparation, Characterization and Property Studies of Carbon Nanostructures Derived from Carbon Rich Materials

Ph.DDOCTOR OF PHILOSOPH

Surface Chemistry Control of 2D Nanomaterial Morphologies, Optoelectronic Responses, and Physicochemical Properties

Indiana University-Purdue University Indianapolis (IUPUI)The field of two-dimensional (2D) nanomaterials first began in earnest with the discovery of graphene in 2004 due to their unique shape-dependent optical, electronic, and mechanical properties. These properties arise due to their one-dimensional confinement and are further influenced by the elemental composition of the inorganic crystal lattice. There has been an intense focus on developing new compositions of 2D nanomaterials to take advantage of their intrinsic beneficial properties in a variety of applications including catalysis, energy storage and harvesting, sensing, and polymer nanocomposites. However, compared to the field of bulk materials, the influence of surface chemistry on 2D nanomaterials is still underdeveloped. 2D nanomaterials are considered an “all-surface” atomic structure with heights of a single to few layers of atoms. The synthetic methods used to produce 2D materials include bottom-up colloidal methods and top-down exfoliation related techniques. Both cases result in poorly controlled surface chemistry with many undercoordinated surface atoms and/or undesirable molecules bound to the surface. Considering the importance surfaces play in most applications (i.e., catalysis and polymer processing) it is imperative to better understand how to manipulate the surface of 2D nanomaterials to unlock their full technological potential. Through a focus of the ligand-surface atom bonding in addition to the overall ligand structure we highlight the ability to direct morphological outcomes in lead free halide perovskites, maximize optoelectronic responses in substoichiometric tungsten oxide, and alter physicochemical properties titanium carbide MXenes. The careful control of precursor materials including poly(ethylene glycol) (PEG) surface ligands during the synthesis of bismuth halide perovskites resulted in the formation of 2D quasi-Ruddlesden-Popper phase nanomaterials. Through small angle X-ray scattering (SAXS) and in conjunction with X-ray photoelectron spectroscopy (XPS) we were able to conclude that an in-situ formation of an amino functional group on our PEG-amine ligand was inserted into the perovskite crystal lattice enabling 2D morphology formation. Additionally, through UV-vis absorption and ultraviolet photoelectron spectroscopies we were able to develop a complete electronic band structure of materials containing varying halides (i.e., Cl, Br, and I). Furthermore, through the increased solubility profile of the PEG ligands we observed solvent controlled assemblies of varying mesostructures. We developed an ex-situ ligand treatment to manipulate the localized surface plasmon resonance (LSPR) response of anion vacancy doped tungsten oxide (WO3-x) nanoplatelets (NPLs). Upon ligand treatment to alter the surface passivating ligand from carboxylic acid containing myristic acid (MA) to tetradecylphosphonic acid (TDPA) we observed a >100 nm blue shift in the LSPR response. Using Fourier transform infrared (FTIR) and Raman spectroscopies in conjunction with DFT calculated Raman spectra we were able to conclude this shift was due to the formation of tridentate phosphonate bonds on the NPLs surface. Phosphonate bonding allows for an increase in surface passivation per ligand decreasing surface trapped electrons. These previously trapped electrons were then able to participate as free electrons in the LSPR response. Electron paramagnetic spectroscopy (EPR) further supported this decrease in surface traps through a decrease and shift of the EPR signal related to metal oxide surface trapped electrons. Lastly, using our knowledge of PEG ligands we were able to modify esterification chemistry to covalently attach PEG ligands to a MXene surface. The successful formation of an ester bond between a carboxylic acid containing PEG ligand and hydroxyl terminating group on the MXene surface was supported by FTIR spectroscopy and thermogravimetric analysis. The attachment of PEG resulted in a drastic change in the hydrophilicity of the MXene surface. Where MXenes were previously only processed in extremely polar solvents the PEG attachment allowed for high dispersibility in a wide range of polar and non-polar organic solvents, effectively increasing their processability. Further, this chemistry was modified to include an additional functional group on the PEG ligand to increase the valency of the post-modification MXene nanoflakes. Overall, work presented in this dissertation represents the development and application of surface chemistry to relatively new 2D nanomaterials. We believe our work significantly increases the knowledge of 2D halide perovskite formation, manipulation of LSPR active metal oxide materials, and the future processing of MXene materials

Synthèse de copolymères de type polymère semi-conducteur-bloc-polymère hydrosoluble (application à la dispersion de nanotubes de carbone)

Cette thèse porte pour l'essentiel sur la synthèse de copolymères à blocs bien définis composés au moins d'un bloc polymère semi-conducteur et d'un segment hydrosoluble pour être utilisés comme agents dispersants de nanotubes de carbone (NTCs) dans des milieux aqueux. Des copolymères de différentes masses molaires ont été synthétisés en suivant des procédés de polymérisation sans métaux et l influence de la fraction volumique de la partie hydrosoluble a été étudiée au regard de leur solubilité en milieux aqueux. La capacité de ces copolymères à s'organiser ou s'auto-assembler tant en solution qu'en film a été examinée. Enfin, des dispersions de NTCs avec ces copolymères ainsi que leurs films obtenus par différents types de dépôts ont été réalisés et caractérisés pour déterminer notamment leurs caractéristiques électro-optiques.Our work focused on the synthesis of well-defined copolymers constituted with at least a conductive polymer segment along with hydrophilic moieties in order to disperse CNTs in aqueous media. Using metal free polymerizations, copolymers with different molecular weights were synthesized in order to study the influence of the hydrophilic part on these materials. Besides the self-assembly behavior of these copolymers, both in bulk and in solution, were addressed. This type of copolymers were successfully used to disperse both single and multi wall carbon nanotubes. Electrical and optical characteristics of the dispersions together with their films will also be discussed.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

The Aqueous Dispersion of Carbon Nanotubes

This work has focused on the use of biological molecules such as amino acids, glycolic acids, ribonucleosides and simple sugars to improve MWCNT aqueous dispersibility through both covalent and non-covalent functionalisation. Oxidative treatment of MWCNTs with 6 M nitric acid has been shown to be a mild, yet effective method for introducing carboxylic acid groups, which are known to improve their dispersion, to the surface. The subsequent ionic interactions of these carboxylic acid groups with selected acidic, basic and neutral amino acids was investigated with a view to this further increasing the aqueous dispersibility of the MWCNTs. Of the amino acids considered basic arginine was found to provide the greatest improvement with the MWCNT concentration increasing from 0.35 to 6.79 mg/mL. The carboxylic acid groups of the oxidised MWCNTs were also used to covalently attach the amino acids through formation of an amide bond. In this instance taurine was found to be the most effective amino acid with dispersibility more than doubling. Non-covalent functionalisation of the MWCNTs was also achieved with taurine functionalised poly(acrylic acid), which resulted in a vefold increase in the concentration of MWCNTs dispersed when compared with poly(acrylic acid). Diazonium chemistry is widely used for the functionalisation of CNTs with aryl groups and in this work a diazonium reaction was used to covalently functionalise MWCNTs with pyridine. These pyridine groups were then used as the basis for the covalent attachment of the sugars ribose, fructose and sucrose. Functionalisation with pyridine alone did not improve the aqueous dispersion of the MWCNTs, however the subsequent attachment of the sugars led to enhanced MWCNT dispersibility with sucrose the most effective at 20 ug/mL. The effect of functionalisation on MWCNT dispersibility was probed using UV-vis- NIR spectroscopy. The modied MWCNTs were further characterised using TGA, TEM, Raman and FTIR spectroscopy