Technology - Nano 201 - Zyvex Perfomance Materials

Nano 201

Due to their high-aspect ratio, small diameter, lightweight, high mechanical strength, high electrical and thermal conductivity, carbon nanotubes (CNTs) have been termed by experts as the material of the 21st century. Fueled by potentially important applications for these materials, CNTs research has increased to a surprising scale, opening new challenges and opportunities for the chemistry of these important structures. The physio-chemical nature of CNTs, which essentially can be viewed as fully conjugated polyaromatic macromolecules with a hollow, inert interior and reactive exterior and ends, drives applications in many fields such as composites, electronics, chemistry and biology.

While fundamental research of CNTs focuses on the intrinsic properties of individual tubes, many commercial applications heavily rely on the interactions of bulk nanotubes with their environment. Due to their high polarizability and smooth surface, CNTs form strong van der Waals interactions between one another, reaching approximately 500 eV per/micrometer of nanotube length. The lack of process-ability and the difficult manipulation in any host matrix have imposed great limitations to the use of CNTs in various applications. In addition, the poor solubility of CNTs in organic solvents and aqueous solutions is a considerable challenge for their manipulation, separation and assembly which, in fact, are key factors in many applications. Furthermore, research shows that un-functionalized sidewalls produce poor adhesion between the nanotubes and the polymer matrix. As a result, previous research and study have failed to produce nanotube/polymer composites that fully realize CNT’s important properties.

To overcome traditional difficulties in CNT integration, and to enable preparation of CNT-reinforced composites, a large-scale effort has been invested into the development of an efficient surface treatment and functionalization technique for improving the dispersion and interfacial interaction of CNTs with various matrices. To date, the main approaches for the surface modification of CNTs can be grouped in two broad categories:

) Covalent functionalization through reactions onto the p-conjugated skeleton of CNTs
) Non-Covalent adsorption or wrapping of various molecules on the side-wall of CNTs

Covalent functionalization has been widely investigated and has produced an array of modified nanotube structures bearing small molecules, polymers and inorganic species. However, sidewall functionalization of CNTs is strongly dependent on the CNT diameter. For example, SWNTs with a smaller diameter have more reactive sidewalls than SWNTs with a larger diameter. Furthermore, changes to CNT properties caused by covalent functionality attached groups can be dramatic and permanent and are not always controllable. As a result, the desired multi-functionality of CNTs may be sacrificed. Additionally, this approach is not amenable to scale-up for high volume and high rate production.

Recognizing the disadvantages associated with each of the major approaches for surface modification of CNTs, ZPM has developed a patented versatile and non-damaging chemistry platform using rigid conjugated polymers and is called Kentera. In this animation, the rigid rod backbone (indicated in white) of Kentera is designed to adhere to the surface of the CNT while the side chains (indicated in red) are designed for enhanced compatibility, adhesion to the host matrix and to create a steric-barrier that prevents aggregation of the nanotubes. The major interaction between the polymer backbone and nanotube surface occurs through π- π interaction. Although π- π interaction is a weaker bond than covalent bonding, the sum of π- interactions creates a large net-stabilizing energy that results in superior and stable systems.

In supramolecular chemistry, p-p interactions are the result of intermolecular overlapping of p-orbitals in p-conjugated systems. This non-covalent interaction becomes stronger as the number of p-electrons increases. The p-p interactions act strongly on flat polycyclic aromatic hydrocarbons, such as anthracene, triphenylene and coronene because of the many delocalized p-electrons

The development of the Kentera technology platform as a non-covalent functionalization method for carbon nanotubes was inspired by the magnitude of p-p interactions in extended p-conjugated systems. By molecular design and by applying the rules and the structural requirement of p-p interactions in host-guest systems, we can design and develop a polymer with strong affinity to CNTs sidewalls. It is even possible to design a conjugated polymer that has irreversible association with CNTs through p-p interactions.

Kentera can be used under a wide range of resin curing regimens because of its thermal stability. An additional distinction of ZPM’s technology is the flexibility of the Kentera platform chemistry that allows ZPM to fine tune the p-p interaction of the backbone to the CNT surface. The overall flexible design of the Kentera platform permits numerous modifications of the backbone and the side chains which in turn make it suitable for various applications. In contrast with other competitive approaches, the Kentera platform works with SWNTs, DWNTs, MWNTs and other graphitized carbon nanomaterials: to date no competing technology can do this.

The benefit to our customers of this unique technology is the transfer of the exceptionally high intrinsic properties of CNTs into a wide variety of polymer composite systems. This transfer of properties enables our customers to utilize our composites and resins to develop and produce lighter, stronger, and stiffer products for their markets.