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

Single-layer graphite oxide can be viewed as an unconventional type of soft material and has recently been recognized as a promising material for composite and electronics applications. It is of both scientific curiosity and technical importance to know how these atomically thin sheets assemble. There are two fundamental geometries of interacting single layers: edge-to-edge and face-to-face. Such interactions were studied at the air−water interface by Langmuir−Blodgett assembly. Stable monolayers of graphite oxide single layers were obtained without the need for any surfactant or stabilizing agent, due to the strong electrostatic repulsion between the 2D confined layers. Such repulsion also prevented the single layers from overlapping during compression, leading to excellent reversibility of the monolayers. In contrast to molecular and hard colloidal particle monolayers, the single layers tend to fold and wrinkle at edges to resist collapsing into multilayers. The monolayers can be transferred to a substr...

Langmuir-Blodgett assembly of graphite oxide single layers.

Critical phenomena and renormalization-group theory

A new structural model for graphite oxide

Graphene nanosheets for enhanced lithium storage in lithium ion batteries

The adiabatic elastic constants of magnesium single crystals have been measured by an ultrasonic pulse technique. The values at 298\ifmmode^\circ\else\textdegree\fi{}K are in good agreement with the recent values of Long and Smith. The values extrapolated to 0\ifmmode^\circ\else\textdegree\fi{}K are ${c}_{11}=0.635$, ${c}_{33}=0.664$, ${c}_{44}=0.1842$, ${c}_{12}=0.259$, ${c}_{13}=0.217$ in units of ${10}^{12}$ dynes/${\mathrm{cm}}^{2}$. A Debye characteristic temperature, $\ensuremath{\theta}$, of 388\ifmmode\pm\else\textpm\fi{}3\ifmmode^\circ\else\textdegree\fi{}K has been calculated at 0\ifmmode^\circ\else\textdegree\fi{}K by averaging the inverse cube of the longitudinal and transverse elastic wave velocities over all directions of propagation. Atomic force constants for a central-force model with an electron gas term are also obtained.

Elastic Constants of Magnesium from 4.2°K to 300°K

MEMBRANES composed of bilayers of amphiphiles such as phospholipids generally exhibit two-dimensional liquid-like structure within the layers. When the constituent molecules of such a membrane are permanently cross-linked to each other, the membrane becomes less flexible, forming a two-dimensional solid. Solid membranes are expected to exhibit very different behaviour from their liquid counterparts1–3, including transitions between a two-dimensional flat phase, a crumpled phase of fractal dimension 2.5 and a compact, three-dimensional phase. Experimental evidence for the crumpled phase has, however, been lacking. As this phase was not observed in computer simulations4–6, it has been suggested that it may always be absent for self-avoiding (and therefore all real) membranes4–6. To the contrary, we report here the experimental observation of the crumpled conformation in an aqueous suspension of graphite oxide membranes. Static light scattering measurements indicate the presence of membrane conformations with a fractal dimension of 2.54 ±0.05. As the intra-membrane affinity is enhanced by changing the composition of the solvent, the membranes collapse to a compact configuration.

Crumpled and collapsed conformation in graphite oxide membranes

High-resolution calorimetric studies have been made of the liquid crystal phase transitions for several dispersions of 70-{Angstrom}-diam silica spheres (aerosil) in octylcyanobiphenyl (8CB) as a function of silica density {rho}{sub S}. The excess specific heat peaks associated with the nematic-isotropic (N-I) and the nematic{endash}smectic-{ital A} (N-SmA) transitions both exhibit shifts to lower temperatures, decreases in the specific heat maximum values, and decreases in the transition enthalpies as {rho}{sub S} is increased. Two distinct regimes of {rho}{sub S}-dependent behaviors are observed with a crossover between them at {rho}{sub S}{congruent}0.1thinspgthinspcm{sup {minus}3}. For lower silica densities, sharp second-order C{sub p} peaks are observed at the N-SmA transitions, characterized by effective critical exponents that decrease monotonically with {rho}{sub S} from the pure 8CB value toward the three-dimensional {ital XY} value, and two closely spaced but distinct first-order C{sub p} features are observed at the N-I transition. For higher silica densities, both the N-SmA and the N-I transitions exhibit a single rounded C{sub p} peak, shifting in temperature and decreasing in total enthalpy in a manner similar to that observed in 8CB+aerogel systems. Small angle x-ray scattering data are qualitatively aerogel-like and yield temperature-independent mass-fractal dimensionalities for aerosil aggregates that differ for samples with silicamore » densities above and below the crossover density. {copyright} {ital 1998} {ital The American Physical Society}« less

https://users.wpi.edu/~gsiannac/pubs_files/prE58p005966y98.pdf

Calorimetric and small angle x-ray scattering study of phase transitions in octylcyanobiphenyl-aerosil dispersions

Light scattering and precision calorimetry show that the nematic ordering of octylcyanobiphenyl (8CB) filling the connected network of pores of a silica aerogel does not occur via the first-order phase transition characteristic of the bulk. Rather, ordering is continuous with an orientational correlation length never increasing beyond the aerogel pore size. The heat-capacity anomly of the second-order nematic--smectic-A phase transition seen in the bulk is absent or greatly broadened in the aerogel.

Phase behavior of the liquid crystal 8CB in a silica aerogel.

A high-resolution computerized calorimeter capable of fully automatic operation in either ac or relaxation modes is described. Emphasis is given to a new version of the relaxation technique in which the heater power is ramped linearly in time. This improvement results in superior performance and convenience in studying both first- and second-order phase transitions and allows quantitative evaluation of latent heats as well as pretransitional heat capacity variations. Examples are given for the use of this calorimeter in the study of liquid crystal phase transitions.

Carl W. Garland

Papers

Elastic Constants of Magnesium from 4.2°K to 300°K

Crumpled and collapsed conformation in graphite oxide membranes

Calorimetric and small angle x-ray scattering study of phase transitions in octylcyanobiphenyl-aerosil dispersions

Phase behavior of the liquid crystal 8CB in a silica aerogel.

Nonadiabatic scanning calorimeter