L. M. Bogdanova

Mechanical properties of epoxy composites based on silver nanoparticles formed in situ

The mechanical and thermomechanical properties of metal-containing epoxy composite films based on silver nanoparticles synthesized in situ are investigated. There is a nonmonotonic dependence of the mechanical properties on the concentration of silver myristate used as a precursor. It is found for the first time that the breaking strength and elastic modulus increase by a factor of 1.8–1.5 relative to those of the unmodified matrix at a small concentration of precursor nanoparticles (on the order of 0.1 wt %). DSC and thermomechanical studies reveal that the glass-transition temperature decreases slightly (by 5–6°C) as the precursor concentration is increased to 0.5 wt %, thereby suggesting a weak plasticization of the modified epoxy matrix. On the basis of the spectrophotometry data measured in the region of surface plasmon resonance of silver nanoparticles (420–425 nm) and SEM data, it is inferred that the in situ strengthening of an epoxy nanocomposite based on epoxy resin ED-20, triethylamine, and silver myristate is attained because silver nanoparticles smaller than 20 nm in size and having a narrow particle-size distribution are formed during curing.

Effect of TiO2 nanoparticle additions on the conductivity of network polymer electrolytes for lithium power sources

Network copolymer electrolytes were synthesized from polyether (polyester) diacrylates with different structures and chain lengths of polyester diacrylate and polyethylene glycol diacrylate. The optimum matrix for ion transport in the electrolyte was formed from only one type of oligomer. The influence of TiO2 nanopowder additions (∼60 nm) on the conductivity of the copolymer electrolyte was studied. The addition of 10 wt % TiO2 led to an increase in the conductivity by an order of magnitude at 30°C; the effective activation energy decreased by 20%. At elevated temperatures, the mobility of polymer chains increased and the contribution of TiO2 nanoparticles in ion transport was only half of the order of magnitude of the conductivity at 100°C. The increase in the conductivity of the polymer electrolyte after the addition of TiO2 was presumably caused by the formation of a more mobile state of the lithium ion near the nanoparticle surface, as shown by pulsed field gradient (PFG) 7Li NMR.

Network polymer electrolytes based on poly(ester diacrylate), ethylene carbonate, and LiClO4

Network polymer electrolytes based on poly(ester diacrylate), LiClO4, and ethylene carbonate are synthesized and investigated via the methods of electrochemical impedance spectroscopy, DSC, and thermal analysis. It is found that, for the polymer-LiClO4 system, the conductivity is 4.2 × 10−7 S/cm at 20°C. With a gradual increase in the amount of ethylene carbonate, the conductivity first decreases and then increases. It is shown that, when poly(ester diacrylate) is crosslinked in ethylene carbonate, up to 45.5% of the latter compound is retained in the polymer and not lost during heating to 100°C. The conductivity of the electrolyte containing 45.6 wt % poly(ester diacrylate), 45.5 wt % ethylene carbonate, 7.5 wt % LiClO4, and 1.4 wt % benzoyl peroxide achieves 1.9 × 10−4 S/cm at 20°C.

New polymer electrolytes based on polyethylene glycol diacrylate–LiBF4–1-ethyl-3-methylimidazolium tetrafluoroborate with the introduction of alkylene carbonates

Polymer gel electrolytes based on polyethylene glycol diacrylate (PEG DA), salt LiBF4, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) were synthesized and studied in the presence of propylene carbonate and ethylene carbonate as solvents. The mechanism of ionic transport in the system was studied using electrochemical impedance spectroscopy, liquid mass spectrometry, pulse-field-gradient spin echo NMR spectroscopy. The range of operating temperatures of the gel electrolytes was determined by DSC. The total conductivity at room temperature in these systems is about 10–3 S cm–1. The self-diffusion coefficients on 7Li nuclei in the systems with a solvent attain the values about 10–10 m2 s–1, and in the PEG DA–LiBF4–EMIBF4 system they range from 10–13 to 10–12 m2 s–1. Ternary associates [(EMI)2(BF4)]+ and [Li+(BF4)2]– were found by liquid mass spectrometry to be the main charge carriers.

Polymer electrolytes based on poly(ester diacrylate), ethylene carbonate, and LiClO4: a relationship of the conductivity and structure of the polymer according to IR spectroscopy and quantum chemical modeling data

New polymer electrolytes based on poly(ester diacrylate) (PEDA), LiClO4, and additives of ethylene carbonate (EC) have a Li+ ion conductivity comparable with that of liquid electrolytes. The conductivity first decreases by an order of magnitude at an EC content of ∼5 wt.% and then increases by three orders of magnitude at 55 wt.% EC. To understand the nature of this extreme dependence, a comprehensive study using IR spectroscopy and quantum chemical modeling was performed. It was found that the changes in the IR spectra with an increase in the EC content were stepwise to form at final stage the same absorption peaks that were observed for the IR spectra of LiClO4 solutions in EC. The density functional theory studies of the energy and structures of mixed Li+ complexes and LiClO4 with EC and PEDA, which was modeled by oligomers H-((CH2)2COO(CH2)2O)n-CH3 (n ≤ 10) showed a stronger binding of the lithium ion with the polymer matrix in the mixed complexes with one EC molecule at a low content of EC resulting, most likely, in a decrease in the conductivity. Less stable mixed complexes with three EC molecules can be formed with an increase in the EC fraction and they become unstable in EC excess because of the transition of the Li+ ions to solvate complexes containing only EC molecules.

Synthesis and free-radical polymerization of water-soluble acrylamide monomers

Water-soluble acrylamide monomers N-(hydroxymethyl)acrylamide, N-(hydroxymethyl)methacrylamide, N,N-diethanolacrylamide, N,N-diethanolmethacrylamide, N,N-methylethanolacrylamide, and N,N-methylethanolmethacrylamide have been synthesized and characterized. The kinetics and thermodynamics of the free-radical polymerization of these monomers and of the model compounds N-isopropylacrylamide and acrylamide have been studied by the methods of isothermal and scanning calorimetry. The structure and the solubility of the said polymers in water and organic solvents have been investigated and their molecular-mass characteristics and temperatures of glass transition (T g) and melting (T m) have been examined by DSC, liquid chromatography, 1H NMR and IR spectroscopy, and chemical analysis of functional groups. Hydrogels and amphiphilic network polymers based on acrylamide monomers have been prepared and characterized.

Synthesis of amphiphilic network copolymers based on poly(ester dimethacrylates)

Poly(ester dimethacrylate) has been synthesized by condensation of the ɛ-caprolactone-based macromonomer and 2-hydroxyethyl methacrylate with dicyclohexylmethane diisocyanate. Network copolymers of different compositions capable of swelling in water, THF, and toluene are obtained by the free-radical copolymerization of poly(ester dimethacrylate) with N-isopropylacrylamide or 2-hydroxyethyl methacrylate. The rate constants and equilibrium swelling indices of network copolymers in these solvents are measured. The amphiphilic properties of the network copolymers can vary in a wide range depending on the composition of copolymers and the nature of a hydrophilic monomer. The copolymers of poly(ester dimethacrylate) with N-isopropylacrylamide are characterized by pronounced thermal sensitivity.

The Study of Formation of Amphiphilic Network Block Copolymer of N -Isopropylacrylamide

The regularities of formation of the structure of amphiphilic network copolymers on radical copolymerization of N-isopropylacrylamide and polyester dimethacrylate are investigated. The kinetic laws of the consumption of functional groups and the increase in the gel content during formation of a crosslinked product are studied. It is shown that the synthesis of crosslinked amphiphilic copolymers proceeds via competing reactions of N-isopropylacrylamide homopolymerization and its copolymerization with polyester dimethacrylate. With the excess of the monofunctional monomer, a homogeneous rubber-like network copolymer is formed, whereas the excess of the bifunctional reagent results in the morphological inhomogeneity of the reaction product.

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10−2–105 Hz. The temperature dependence of σ dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ dc = σ dc0exp{‒DT 0/(T-T 0)} (where T 0 is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T g. At the same time, T 0 does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T g. The value of σ dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T g. The obtained dependence of σ dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.

Kinetics of the thermal degradation of polycarbonate films containing silver nanoparticles

The kinetic features of thermal degradation of polycarbonate films containing 0.02–0.13 wt % silver are investigated. The analysis of surface plasmon resonance spectra shows that the composite films contain silver nanoparticles with sizes from 10 to 200 nm. The shapes and sizes of particles are determined via scanning electron microscopy. It is shown that the rates of thermal degradation of the nanocomposites are much higher than the rate of degradation of the initial polycarbonate; the highest catalytic activity is exhibited by spherical silver nanoparticles with sizes below than 40 nm, while particles shaped as bipyramids and having sizes of 100–200 nm are less active catalytically.