Elucidation of the reinforcing mechanism in carbon nanotube/rubber nanocomposites.

High-performance sealants using rubber composites containing multiwalled carbon nanotubes (MWNTs) were developed in order to probe and excavate oil in deeper wells. However, the stress-strain behavior and the reinforcing mechanism of highly concentrated MWNT/rubber composites subjected to large deformation remain largely unexplored. Here we report on the complete stress-strain relationships of MWNT/rubber composites under uniaxial tension before rupture, with a suggestion of a novel reinforcement effect of high concentration of MWNTs. A theoretical model is developed to understand the reinforcing mechanism and estimate the mechanical properties of MWNT/rubber composites under large deformation. We have demonstrated that persistence length and reorientation of MWNTs during stretch have a significant impact on mechanical properties, such as the modulus of the rubber composite. These results provide guidelines for developing MWNT-reinforced composites to achieve desired nonlinear and extreme mechanical performance for a wide range of applications.

Self-organization of low-symmetry adjacent-type metallophthalocyanines having branched alkyl chains.

Low-symmetry, adjacent-type metallophthalocyanines 1 and 2 with four branched alkyl chains on one side and a chiral bridging segment on the other were synthesized, and their self-organization properties were investigated. The synthesized adjacent-type phthalocyanines were liquid-crystalline and exhibited a phase transition from the crystalline phase to the mesophase below room temperature. X-ray diffraction indicated that the molecules are stacked in one-dimensional columnar aggregates with a hexagonal arrangement. The self-organization behavior of zinc complex 1 and cobalt complex 2 was also investigated with a monolayer experiment at the air-water interface. The adjacent-type phthalocyanines formed a stable monolayer at the air-water interface, and the monolayers could be transferred onto quartz substrates by a Y-type deposition. UV-vis, XRD, and CD measurements for the resulting Langmuir-Blodgett films indicated that 1 and 2 had different molecular orientations.

Nanoscopic fibrous assemblies made of metallophthalocyanine-terminated amphiphilic polymers.

Atom-transfer radical polymerization (ATRP) of acrylates from the initiator-modified zinc phthalocyanine yielded amphiphilic, phthalocyanine-terminated polymers with a narrow molecular-weight distribution. The disklike phthalocyanine moiety was incorporated into one end of the polymer chain. We investigated the aggregation behavior of phthalocyanine-terminated polymers in solution and in the solid state by using UV-visible, FT-IR, differential scanning calorimetry (DSC), and temperature-controlled powder X-ray diffraction (XRD) measurements. Amphiphilic phthalocaynine-terminated polymers that possess a poly[tri(ethylene glycol)methyl ether acrylate] chain aggregate in methanol to form a physical gel. Images from atomic force microscopy (AFM) and transmission electron microscopy (TEM) indicate that the physical gel contains a dense fibrous network structure, in which the zinc phthalocyanine groups were stacked into one-dimensional columnar aggregates through intermolecular pi-pi interactions between the pi-conjugated phthalocyanines and through van der Waals interaction of alkyl chains.