Emmanuel P. Giannelis

Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes

The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations.

Polymer-layered silicate nanocomposites : Synthesis, properties and applications

Polymer nanocomposites, especially polymer-layered silicate (PLS) nanocomposites, represent a radical alternative to conventionally (macroscopically) filled polymers. Because of their nanometer-size dispersion, the nanocomposites exhibit markedly improved properties when compared with the pure polymers or conventional composites. These include increased modulus and strength, decreased gas permeability, increased solvent and heat resistance and decreased flammability. In addition to their potential applications, PLS nanocomposites are also unique model systems to study the structure and dynamics of polymers in confined environments. Using both delaminated and intercalated hybrids, the statics and dynamics of polymers confined over distances ranging from the radius of gyration of the polymer to the statistical segment length of the chains can be studied.

Formation Mechanism of Carbogenic Nanoparticles with Dual Photoluminescence Emission

We present a systematic investigation of the formation mechanism of carbogenic nanoparticles (CNPs), otherwise referred to as C-dots, by following the pyrolysis of citric acid (CA)-ethanolamine (EA) precursor at different temperatures. Pyrolysis at 180 °C leads to a CNP molecular precursor with a strongly intense photoluminescence (PL) spectrum and high quantum yield formed by dehydration of CA-EA. At higher temperatures (230 °C) a carbogenic core starts forming and the PL is due to the presence of both molecular fluorophores and the carbogenic core. CNPs that exhibit mostly or exclusively PL arising from carbogenic cores are obtained at even higher temperatures (300 and 400 °C, respectively). Since the molecular fluorophores predominate at low pyrolysis temperatures while the carbogenic core starts forming at higher temperatures, the PL behavior of CNPs strongly depends on the conditions used for their synthesis.

New advances in polymer/layered silicate nanocomposites

This review discusses some recent advances in polymer silicate nanocomposites. In particular, we highlight the properties of specific nanocomposites while emphasizing the lack of properties trade-offs in these systems. We also present our work on the structure and dynamics of the polymer/nanofiller interface and attempt to relate them to macroscopic nanocomposite properties.

High efficiency nanocomposite sorbents for CO2 capture based on amine-functionalized mesoporous capsules

A novel high efficiency nanocomposite sorbent for CO2 capture has been developed based on oligomeric amine (polyethylenimine, PEI, and tetraethylenepentamine, TEPA) functionalized mesoporous silica capsules. The newly synthesized sorbents exhibit extraordinary capture capacity up to 7.9 mmol g−1 under simulated flue gas conditions (pre-humidified 10% CO2). The CO2 capture kinetics were found to be fast and reached 90% of the total capacities within the first few minutes. The effects of the mesoporous capsule features such as particle size and shell thickness on CO2 capture capacity were investigated. Larger particle size, higher interior void volume and thinner mesoporous shell thickness all improved the CO2 capacity of the sorbents. PEI impregnated sorbents showed good reversibility and stability during cyclic adsorption–regeneration tests (50 cycles).

Relaxations of confined chains in polymer nanocomposites: Glass transition properties of poly(ethylene oxide) intercalated in montmorillonite

The relaxation behavior of poly(ethylene oxide) (PEO), intercalated in montmorillonite, a naturally occurring mica-type silicate, was studied by differential scanning calorimetry ( DSC and thermally stimulated dielectric depolarization ( or thermally stimulated current, TSC). The materials were synthesized by melt or solution-mediated intercalation. In both intercalates, the PEO chains were confined to ca. 0.8-nm galleries between the silicate layers. The solution intercalate contained a fraction of uninterca-lated PEO chains which exhibited a weak and depressed PEO melting endotherm in DSC. In contrast, the melt intercalate was starved such that almost all the PEO chains were effectively intercalated. For these melt intercalates, no thermal events were detected by DSC. TSC thermal sampling technique was used to examine the glass transition regions and to estimate the extent of cooperativity of chain motions. The motions of the intercalated PEO chains are inherently noncooperative relative to the cooperative T g motions in the amorphous portion of the bulk polymer. This is presumably due to the strong confining effect of the silicate layers on the relaxations of the intercalated polymer.

Polymer nanocomposites: a new strategy for synthesizing solid electrolytes for rechargeable lithium batteries

Abstract The ionic conductivity and lithium electrode-electrolyte interfacial stability have been measured for composite polymer electrolytes using micrometer- and nanometer-size alumina (Al2O3) with polyethylene oxide (PEO) and lithium tetrafluoroborate (LiBF4). The influence of the nanometer-size alumina particles increases ionic conductivity by an order of magnitude compared with micrometer-size particles. The interfacial stability is increased a factor of two. Characterization of layered nanocomposite polymer electrolytes based upon melt intercalation of PEO in layered silicates (montmorillonite) show that the intercalated PEO is amorphous.

MOLECULAR DYNAMICS SIMULATIONS OF ORGANICALLY MODIFIED LAYERED SILICATES

Molecular dynamics (MD) simulations are used to study the static and dynamic properties of 2:1 layered silicates ion exchanged with alkyl-ammonium surfactants. These systems are in the form of oligomeric alkanes grafted by cationic groups on atomically smooth crystalline layers 10 A thick and several microns wide. The organically modified layers self-assemble parallel to each other to form alternating, well-ordered organic/inorganic multilayers. By studying the systems at the experimentally measured layer separations, computer modeling directly provides the structure and dynamics of the intercalated surfactant molecules. The grafted-chain conformations are also expressed through the trans-gauche conformer ratios and transition frequencies which compare well with Fourier transform infrared spectroscopy (FTIR) experiments.

Multifunctional Graphene/Platinum/Nafion Hybrids via Ice Templating

We report the synthesis of multifunctional hybrids in both films and bulk form, combining electrical and ionic conductivity with porosity and catalytic activity. The hybrids are synthesized by a two-step process: (a) ice templation of an aqueous suspension comprised of Nafion, graphite oxide, and chloroplatinic acid to form a microcellular porous network and (b) mild reduction in hydrazine or monosodium citrate which leads to graphene-supported Pt nanoparticles on a Nafion scaffold.

Study of the interlayer expansion mechanism and thermal-mechanical properties of surface-initiated epoxy nanocomposites

Abstract The exfoliation mechanism and thermal–mechanical properties of surface-initiated epoxy nanocomposites were studied. Time-resolved high-temperature X-ray diffraction, DSC, and isothermal rheological analyses revealed that the interlayer expansion mechanism might be separated into three stages. These stages relate to the initial interlayer expansion, the steady-state interlayer expansion, and the cessation of interlayer expansion. It was found that differences in the activation energies of interlayer expansion and of curing influence the final nanostructures of the materials. The thermal–mechanical properties of the nanocomposites were studied using dynamic mechanical thermal analysis. Variations in ultimate properties were attributed to the formation of an interphase layer, where the interphase is hypothesized to be the epoxy matrix plasticized by surfactant chains.