A new method for the preparation of graphene nanoplatelets (GNP) from graphite intercalation compounds (GICs) was investigated. Donor-type ternary GICs of natural graphites, lithium ions and tetrahydrofurane (NG-Li-THF) were synthesized via a solution process, with the lithium ions in the GICs then exchanged with different tetra alkyl ammonium cations to expand the interlayer distance (d-spacing) of these GICs. Microwave irradiation of these GICs resulted in the exfoliation of GICs, forming so-called 'worm-like exfoliated graphites.' Sonication of the worm-like exfoliated graphites in acetone resulted in GNPs with different aspect ratios. Powder X-ray diffractometry, scanning electron microscopy and transmission electron microscopy were employed to characterize the GICs and GNPs. It was found that the ion-exchange of NG-Li-THF increased the volume expansion ratios, and the molecular structure of the tetra alkyl ammonium cations affected the aspect ratios of the GNPs after exfoliation.

A resin mixture of vinyl ester and carboxyl terminated butadiene diluted with styrene shows an increase of viscosity when shearing the sample. Unlike previous reports on rheopexy and shear induced gelation of unfilled systems, this behavior leads to permanently elevated levels of viscosity. FT-IR found no indication of a chemical reaction, and therefore, the changes must be physical in naturebelieved to be an increase in the number of hydrogen bonds. On the basis of the results, it is concluded that a physical network based on supramolecular attractions between the −COOH groups of the carboxyl terminated butadiene is formed, which leads to a time-dependent behavior and increase in viscosity at certain shear rate, at longer shearing times. This is a new effect, which we call "irreversible shear induced gelation by supramolecular bonding".

The rheological properties of epoxy resins filled with organoclay and colloidal nanosilica were investigated by employing a parallel plate rheometer in flow mode at 25 degrees C. Shear thickening and shear thinning behaviors were observed in the epoxy resins filled with a mixture of organoclay and colloidal nanosilica. Minima were observed in the relaxation time of the systems consisting of epoxy resins filled with organoclay and colloidal silica as the content of colloidal nanosilica was increased. It seems that the colloidal nanosilica increased the mobility of the filled epoxy resins and reduced the interactions between the silicate layers in the systems.

No abstract