Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...

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Graphene/Polymer Nanocomposites

Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.

Silica-based mesoporous organic-inorganic hybrid materials.

Ordered mesoporous materials in catalysis

Water gelation by small organic molecules.

Vesicles consisting of a bilayer membrane of amphiphilic lipid molecules are remarkably flexible surfaces that show an amazing variety of shapes of different symmetry and topology. Owing to the fluidity of the membrane, shape transitions such as budding can be induced by temperature changes or the action of optical tweezers. Thermally excited shape fluctuations are both strong and slow enough to be visible by video microscopy. Depending on the physical conditions, vesicles adhere to and unbind from each other or a substrate. This article describes the systematic physical theory developed to understand the static and dynamic aspects of membrane and vesicle configurations. The preferred shapes arise from a competition between curvature energy, which derives from the bending elasticity of the membrane, geometrical constraints such as fixed surface area and fixed enclosed volume, and a signature of the bilayer aspect. These shapes of lowest energy are arranged into phase diagrams, which separate regi...

Configurations of fluid membranes and vesicles

Many types of amphiphilic molecules self-assemble in solution to form cylindrical tubules and helical ribbons. Some examples include diacetylenic lipids, amide amphiphiles, bile, and diblock copolymers. Researchers have proposed a variety of models to explain the formation of these high-curvature structures. These models can be divided into two broad categories:  models based on the chiral elastic properties of membranes, and models based on other effects, including electrostatic interactions, elasticity of orientational order, and spontaneous curvature. In this paper, we review the range of theoretical approaches and compare them with relevant experiments. We argue that the category of models based on chiral elastic properties provides the most likely explanation of current experimental results, and we propose further theoretical and experimental research to give a more detailed test of these models.

Theory of Self-Assembled Tubules and Helical Ribbons

Ordered mesoporous materials have been synthesized by co-condensation of bis(triethoxysilyl)ethane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS) under basic conditions with supramolecular templates of cetyltrimethylammonium chloride as structure-directing agents Incorporation of the templates into the mesoscopic composite was followed by surfactant extraction to form periodic mesoporous organosilicas These materials have been characterized by powder X-ray diffraction, nitrogen gas sorption, metal ion adsorption, elemental analysis, and high resolution thermogravimetric analysis The effects of AAPTS concentration in the initial solutions on the chemical and structural properties of the final products are examined

Amine-Functionalized Periodic Mesoporous Organosilicas

Methylene-, ethylene-, and phenylene-bridged periodic mesoporous organosilicas (PMOs) synthesized with nonionic alkylethylene oxide templates exhibited significantly better mechanical and hydrothermal stabilities than periodic mesoporous silica. Synthesis of PMOs utilized the acid-catalyzed hydrolysis and condensation of bis(triethoxysilyl) precursors around supramolecular polyoxyethylene(10) stearyl ether (Brij 76) templates. Nitrogen gas sorption, thermogravimetry, and X-ray diffraction have been used to characterize the effects of aging, mechanical compression, and hydrothermal treatment on these materials. Both as-synthesized composites containing surfactant templates and extracted PMOs showed no degradation after 10 months. The enhanced stability of these nanoporous organosilicas relative to meoporous silica makes them potential candidates for use in advanced catalysis and adsorption applications.

Mechanical and Hydrothermal Stabilities of Aged Periodic Mesoporous Organosilicas

Several techniques for controlling the morphology of self-assembled lipid tubules are investigated by using circular dichroism spectroscopy and electron microscopy. These studies show that variations in the molecular structure of the diacetylenic phospholipid, lipid concentration, and solution conditions allow for control of the number of bilayers in the tubule walls, but not their diameter. Tubules formed in water and mixtures of alcohols adopt interesting morphologies and allow for further control of tubule structure. In addition, studies of lipids with different acyl chains show that tubule morphology is sensitive to the degree of order within the chains. Because of the chiral molecular architecture in lipid tubules, intense peaks in their circular dichroism spectra are observed. These peaks can be monitored to obtain information on the tubule morphology. This information is correlated to direct observations made using electron microscopy. Results of these studies have led to the optimization of large ...

Controlling the Morphology of Chiral Lipid Tubules

Arylene- and ethylene-bridged polysilsesquioxane materials have been synthesized by the hydrolysis and condensation of alkoxysilyl precursors under basic conditions. Cetyltrimethylammonium chloride was used to increase the porosity and surface areas of these materials via the surfactant template approach. Structural characterization of these materials was carried out by nitrogen gas sorption and X-ray diffraction. The adsorption of three phenolic compounds (4-nitrophenol, 4-chlorophenol, 4-methylphenol) has been investigated by both batch and column testing. The arylene-bridged material exhibited a much greater affinity for all three phenols. The efficient removal of adsorbed phenols by a simple ethanol wash led to sorbent regeneration and separation of the aromatic species.

Mark S. Spector

Papers

Theory of Self-Assembled Tubules and Helical Ribbons

Amine-Functionalized Periodic Mesoporous Organosilicas

Mechanical and Hydrothermal Stabilities of Aged Periodic Mesoporous Organosilicas

Controlling the Morphology of Chiral Lipid Tubules

Porous polysilsesquioxanes for the adsorption of phenols.