Seisuke Ata

Mechanically Durable and Highly Conductive Elastomeric Composites from Long Single-Walled Carbon Nanotubes Mimicking the Chain Structure of Polymers

By using long single-walled carbon nanotubes (SWNTs) as a filler possessing the highest aspect ratio and small diameter, we mimicked the chain structure of polymers in the matrix and realized a highly conductive elastomeric composite (30 S/cm) with an excellent mechanical durability (4500 strain cycles until failure), far superior to any other reported conductive elastomers. This exceptional mechanical durability was explained by the ability of long and traversing SWNTs to deform in concert with the elastomer with minimum stress concentration at their interfaces. The conductivity was sufficient to operate many active electronics components, and thus this material would be useful for practical stretchable electronic devices.

Elastomeric Thermal Interface Materials with High Through‐Plane Thermal Conductivity from Carbon Fiber Fillers Vertically Aligned by Electrostatic Flocking

Electrostatic flocking is applied to create an array of aligned carbon fibers from which an elastomeric thermal interface material (TIM) can be fabricated with a high through-plane thermal conductivity of 23.3 W/mK. A high thermal conductivity can be achieved with a significantly low filler level (13.2 wt%). As a result, this material retains the intrinsic properties of the matrix, i.e., elastomeric behavior.

Controlling exfoliation in order to minimize damage during dispersion of long SWCNTs for advanced composites

We propose an approach to disperse long single-wall carbon nanotubes (SWCNTs) in a manner that is most suitable for the fabrication of high-performance composites. We compare three general classes of dispersion mechanisms, which encompass 11 different dispersion methods, and we have dispersed long SWCNTs, short multi-wall carbon nanotubes, and short SWCNTs in order to understand the most appropriate dispersion methods for the different types of CNTs. From this study, we have found that the turbulent flow methods, as represented by the Nanomizer and high-pressure jet mill methods, produced unique and superior dispersibility of long SWCNTs, which was advantageous for the fabrication of highly conductive composites. The results were interpreted to imply that the biaxial shearing force caused an exfoliation effect to disperse the long SWCNTs homogeneously while suppressing damage. A conceptual model was developed to explain this dispersion mechanism, which is important for future work on advanced CNT composites.

A dispersion strategy: dendritic carbon nanotube network dispersion for advanced composites

We propose a strategy utilizing carbon nanotube (CNT) agglomerates in solution, typically undesired precipitates from dispersions of isolated CNTs, for fabricating advanced composites. Importantly, long, single-walled carbon nanotubes (SWNTs) were necessary to make highly concentrated (above 3.0 wt%) and very stable CNT suspensions. SWNTs in the agglomerates formed a dendritic network similar to venation and vein patterns observed in nature. Through this strategy, we demonstrated a 10-fold increase in electrical conductivity of a rubber-composite. Our results showed that the two CNT dispersion strategies, i.e., isolated CNTs, and dendritic CNT agglomerates are complementary, and each demonstrated distinct advantages and disadvantages, and their application is intended toward different uses; our results show the individual values of each approach.

Influence of matching solubility parameter of polymer matrix and CNT on electrical conductivity of CNT/rubber composite

We report a general approach to fabricate elastomeric composites possessing high electrical conductivity for applications ranging from wireless charging interfaces to stretchable electronics. By using arbitrary nine kinds of rubbers as matrices, we experimentally demonstrate that the matching the solubility parameter of CNTs and the rubber matrix is important to achieve higher electrical conductivity in CNT/rubber composite, resulting in continuous conductive pathways leading to electrical conductivities as high as 15 S/cm with 10 vol% CNT in fluorinated rubber. Further, using thermodynamic considerations, we demonstrate an approach to mix CNTs to arbitrary rubber matrices regardless of solubility parameter of matrices by adding small amounts of fluorinated rubber as a polymeric-compatibilizer of CNTs. We thereby achieved electrical conductivities ranging from 1.2 to 13.8 S/cm (10 vol% CNTs) using nine varieties of rubber matrices differing in chemical structures and physical properties. Finally, we investigated the components of solubility parameter of CNT by using Hansen solubility parameters, these findings may useful for controlling solubility parameter of CNTs.

Stretchable electromagnetic-interference shielding materials made of a long single-walled carbon-nanotube–elastomer composite

By using long single-walled carbon nanotubes that possess a high aspect ratio and small diameter as fillers, we introduced electromagnetic interference (EMI) shielding to a fluorinated rubber without hardening and embrittling it. A sheet of this material with a thickness of 0.2 mm could decrease more than 90% of the strength of incident electromagnetic waves at microwave frequencies. Further, this material has a sufficient flexibility, which enables it to elongate to double its original length without any cracking, and has a higher mechanical strength than commercialized generic stocking (3.1 times the maximum tensile stress and 2.4 times the tear strength). Therefore, this material is useful for flexible and stretchable EMI shielding sheets that can wrap an arbitrarily shaped radiating object. This feature can be attributed to the fact that the carbon nanotubes could induce EMI shielding at a low loading level (only 1 wt%) without breaking the structure of the rubber matrix.