Yuliia Bolbukh

Electrokinetic Properties of the Pristine and Oxidized MWCNT Depending on the Electrolyte Type and Concentration

Electrostatic stabilization is reduced in its efficiency in an electrolyte-containing environment. The effect of electrolyte concentration is mostly described as negative factor for dispersion stabilization. Usually, zeta potential and physical stability decrease at increasing electrolyte concentration. The purpose of the present study was to measure the surface properties of nanotubes in aqueous solution of monovalent electrolytes at different concentration. Characteristics such as size distribution, surface chemistry, surface charge, and dispersability in aqueous phase have been identified. Hydrodynamic size and zeta potential in aqueous multiwalled carbon nanotube (MWCNT) suspensions were determined at different pH with the desired concentrations of electrolyte of the cationic group (NaCl, KCl, CsCl) and the anionic group (NaClO4). The correlations between the response of the surface functionality of pristine and oxidized multiwalled carbon nanotubes and electrical double layer (EDL) forming at different ionic environments in the vicinity of a nanotube surface were determined. The nanotube dispersion stabilization was found to be more affected by ion size and pH medium then electrolyte concentration. The data obtained confirms the predominant role of surface reactions. The most stable dispersion of nanotubes was achieved in KCl electrolyte solution at less negative charge of the surface.

Modified silicas with different structure of grafted methylphenylsiloxane layer

The method of a chemical assembly of the surface polymeric layer with high contents of the modifying agent was developed. Powders of nanodispersed silica with chemisorbed polymethylphenylsiloxane (PMPS) were synthesized by solvent-free chemical assembly technique with a dimethyl carbonate (DMC) as scission agent. Samples were characterized using FTIR spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), and elemental analysis (CHN analysis). Coating microstructure, morphology, and hydrophilic-hydrophobic properties of nanoparticles were estimated. The results indicate a significant effect of the PMPS/DMC ratio at each modification stage on hydrophobic properties of modified silicas. Modification with a similar composition of the PMPS/DMC mixture, even with different polymer amount at each stage, provides the worst hydrophobicity. Results suggest that the highest hydrophobicity (contact angle θ = 135°–140°) is achieved in the case when silica modified with the PMPS/DMC mixture using multistage approach that providing a formation of the monomolecular layer of polysiloxane at the first modification step. The characteristics of surface structure were interpreted in terms of density of polymer-silica bonds at the interfaces that, usually, are reduced for modified surfaces, in a coupling with conformation model that accented the shape of chains (arch- and console-like) adsorbed on solid surfaces.

Effect of Surface Hydride, Vinyl, and Methyl Groups on Thermal Stability of Modified Silica-Divinylbenzene-Di(Methacryloyloxymethyl)Naphthalene Composites

Divinylbenzene (DVB)-di(methacryloyloxymethyl)naphthalene (DMN)/modified silica composites were studied by means of IR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The results show that filling with modified fumed silica decreases the initial temperature of DVB-DMN copolymer thermal-oxidative degradation; however, the activation energy of this process generally increases. The partial modification of silica surface turned out to be more efficient than the total functionalization and silicas containing surface methyl in combination with hydride groups were found to be the best fillers for DVB-DMN copolymer among all those investigated.

Hydroxyapatite composites with multiwalled carbon nanotubes

The structure of composites based on hydroxyapatite filled with multiwalled carbon nanotubes was investigated using differential scanning calorimetry analysis and X-ray diffraction spectroscopy. Hydroxyapatite was prepared by the wet synthesis in the presence of pristine and oxidised carbon nanotubes. An influence of nature of functional groups of the nanotubes boundary layer on a crystallinity of the inorganic part was evaluated using differential scanning calorimetry analysis and X-ray diffraction spectroscopy. Morphology of composites obtained was studied by nitrogen adsorption/desorption technique and scanning electron microscopy. The hydroxyapatite/nanotubes interface was characterised using electrochemical methods. The parameters of the electrical double layer: A density of surface charge versus pH, zeta potential versus pH were described. The study has shown that the synthesis of hydroxyapatite/nanotube composites by formation of inorganic part in the presence of carbon filler significantly affect the microstructure, phase composition, crystallinity, hydroxyl content, chemical composition of the mineral part, as well as thermal properties and electrokinetic properties of composite.

Silver nanoparticles deposited on pyrogenic silica solids: Preparation and textural properties

Silver-based nanomaterials and composites are important components in materials science and engineering due to the reactivity of silver nanophase based on exceptional surface effects. Ag-doped SiO2 nanocomposites were synthesized by wet impregnation procedure of aminopropyl-functionalized silica materials with submicrometer structure. Aminopropyl-functionalized pyrogenic silicon dioxide with amount of amino groups established as half and close to full monolayer was used to immobilize the nanosilver phase obtained from ammoniacal silver complex as a noble metal precursor. Pyrogenic silicon dioxide as an inexpensive nanostructured material with useful properties including adsorptive affinity for noble metal ions and organic macromolecules was applied as a support for diamminesilver(I) ions and finally for silver nanoparticles. In the present study, the effect of amino-functionalization and silver nanoparticles deposition was monitored by investigation of the textural properties and thermal stability of obtained nanocomposites. The properties of the nanocomposites were investigated by transmission electron microscopy, nitrogen adsorption–desorption isotherms, and thermal analysis (thermogravimetry/differential scanning calorimetry).

Immobilization of Polymeric Luminophor on Nanoparticles Surface.

Polymeric luminophors with reduced toxicity are of the priorities in the production of lighting devices, sensors, detectors, bioassays or diagnostic systems. The aim of this study was to develop a method of immobilization of the new luminophor on a surface of nanoparticles and investigation of the structure of the grafted layer. Monomer 2,7-(2-hydroxy-3-methacryloyloxypropoxy)naphthalene (2,7-NAF.DM) with luminophoric properties was immobilized on silica and carbon nanotubes in two ways: mechanical mixing with previously obtained polymer and by in situ oligomerization with chemisorption after carrier’s modification with vinyl groups. The attached polymeric (or oligomeric) surface layer was studied using thermal and spectral techniques. Obtained results confirm the chemisorption of luminophor on the nanotubes and silica nanoparticles at the elaborated synthesis techniques. The microstructure of 2,7-NAF.DM molecules after chemisorption was found to be not changed. The elaborated modification approach allows one to obtain nanoparticles uniformly covered with polymeric luminophor.

DSC study of silicas with immobilized polysiloxane layer of different architecture

Core–shell structured nanocomposites of polydimethylsiloxane with different polymerization degree (PMS100 and PMS50) and polymethylphenylsiloxane (PMPS4) immobilized onto fumed silica nanoparticles were studied by means of differential scanning calorimetry. The polysiloxanes were attached to the particles’ surface using thermally stimulated binding and modification in the presence of depolymerization activator—dimethyl carbonate (DMC). Single- and multi-stage processes were applied in order to obtain a different architecture of polymeric layer on the silica nanoparticles surface. The effect of polysiloxane/DMC ratio on phase transitions of obtained polymeric layers was evaluated. The grafting of polydimethylsiloxane at the presence of chain scissor resulted in cross-linking of the attached polymeric layers. When using a multi-step modification with PMPS, a dense cross-linked layer was formed on the silica surface. Unlike the samples obtained by one-step modification with different polymer content, for which the amount of polymer attached to silica surface changes the parameters of the relaxation process in polymeric layer, for composites synthesized using multi-stage modification, a greater influence has the length of the oligomer introduced on first stage. The best results were achieved for composite with PMPS when using on the first stage of modification the PMPS/DMC mixture with low content of depolymerization agent (oligomers with long chain, respectively). A notable increase in the mobility of the polymeric layer was detected due to the formation of isotactic macromolecular chains.

Effect of Carbon Nanotubes Surface Modification on Structure of Forcibly Ordered Films of Filled Polystyrene

The effect of surface modification of multi-walled carbon nanotubes (MWCNTs) with different modifiers on the filler dispersibility in polystyrene and the influence of the external magnetostatic field on the structure of obtained composites have been studied. The surface modification of as-synthesised and oxidized carbon nanotubes was performed by treatment with hydrochloric acid or ammonia hydroxide solutions. The composite films were casted on glass plates with or without the influence of magnetostatic field at the desired directions of the magnetic lines. A combination of MWCNTs surface treatment and directed influence of the magnetostatic field was shown to be an effective route to change the structure of composites.