Buckypaper is a thin sheet made from an aggregate of

carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

or carbon nanotube grid paper. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups, showing promise as

vehicle armor Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fighti ...

personal armor Body armor, also known as body armour, personal armor or armour, or a suit or coat of armor, is protective clothing designed to absorb or deflect physical attacks. Historically used to protect military personnel, today it is also used by variou ...

, and next-generation

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

and displays.

Background

Buckypaper is a macroscopic aggregate of carbon nanotubes (CNT), or "buckytubes". It owes its name to the

buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a soccer ball. Each of its 60 carbon atoms is bonded ...

, the 60 carbon

fullerene A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...

(an

allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...

of carbon with similar bonding that is sometimes referred to as a "Buckyball" in honor of R. Buckminster Fuller).

Synthesis

The generally accepted methods of making CNT films involves the use of

surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...

s, such as

Triton X-100 Triton X-100 (''n'') is a nonionic surfactant that has a hydrophilic polyethylene oxide chain (on average it has 9.5 ethylene oxide units) and an aromatic hydrocarbon lipophilic or hydrophobic group. The hydrocarbon group is a 4-( 1,1,3,3-tetramet ...

and

sodium lauryl sulfate Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium Salt ...

, which improves their dispersibility in aqueous solution. These suspensions can then be membrane filtered under positive or negative pressure to yield uniform films. The

van der Waals force In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...

's interaction between the nanotube surface and the surfactant can often be mechanically strong and quite stable and therefore there are no assurances that all the surfactant is removed from the CNT film after formation. Washing with methanol, an effective solvent in the removal of Triton X, was found to cause cracking and deformation of the film. It has also been found that Triton X can lead to cell lysis and in turn tissue inflammatory responses even at low concentrations. In order to avoid adverse side-effects from the possible presence of surfactants, an alternative casting process can be used involving a

frit compression Frit compression is the technique used to fabricate buckypaper and buckydiscs from a suspension of carbon nanotubes in a solvent. This is a quick, efficient method over surfactant-casting or acid oxidation filtration of carbon nanotubes. Background ...

method that did not require the use of surfactants or surface modification. The dimensions can be controlled through the size of the syringe housing and through the mass of carbon nanotubes added. Their thicknesses are typically much larger than surfactant-cast buckypaper and have been synthesized from 120 μm up to 650 μm; whilst no nomenclature system exists to govern thicknesses for samples to be classified as paper, samples with thicknesses greater than 500 μm are referred to as buckydiscs. The frit compression method allows rapid casting of buckypaper and buckydiscs with recovery of the casting solvent and control over the 2D and 3D geometry. Aligned multi-walled carbon nanotube (MWNT) growth has been used in CNT film synthesis through the

domino effect A domino effect or chain reaction is the cumulative effect generated when a particular event triggers a chain of similar events. This term is best known as a mechanical effect and is used as an analogy to a falling row of dominoes. It typically ...

. In this process, "forests" of MWNTs are pushed flat in a single direction, compressing their vertical orientation into the horizontal plane, which results in the formation of high-purity buckypaper with no further purification or treatment required. By comparison, when a buckypaper sample was formed from the 1 ton compression of chemical vapor deposition (CVD) generated MWNT powder, any application of a solvent led to the immediate swelling of the film till it reverted into particulate matter. It appears that for the CNT powder used, compression alone was insufficient to generate robust buckypaper and highlights that the aligned growth methodology generates ''in situ'' tube-tube interactions not found in CVD CNT powder and are preserved through to the domino pushing formation of buckypaper. Recently, a new scalable CNT film fabrication method has been developed: Surface-Engineered Tape Casting (SETC) technique. The SETC technique solves the main challenge of tape-casting which is the detachment of the dried and the typically sticky CNT film from the supporting-substrate. To achieve a perfect detached film, the supporting-substrate has to be engineered with micro-pyramid pore structure morphology. SETC produces large area films from any commercially available carbon nanotubes with tunable length, thickness, density and composition.

Properties

Buckypaper is one tenth the weight yet potentially 500 times stronger than steel when its sheets are stacked to form a composite. It could disperse heat like brass or steel and it could conduct electricity like copper or silicon.

Applications

Among the possible uses for buckypaper that are being researched: *Fire protection: covering material with a thin layer of buckypaper significantly improves its fire resistance due to the efficient reflection of heat by the dense, compact layer of carbon nanotubes or carbon fibers. *If exposed to an

electric charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respe ...

, buckypaper could be used to illuminate computer and television screens. It could be more energy-efficient, lighter, and could allow for a more uniform level of brightness than current

cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...

(CRT) and

liquid crystal display A liquid-crystal display (LCD) is a flat panel display, flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liqui ...

(LCD) technology. *Since individual carbon nanotubes are one of the most thermally conductive materials known, buckypaper lends itself to the development of heat sinks that would allow computers and other electronic equipment to disperse heat more efficiently than is currently possible. This, in turn, could lead to even greater advances in electronic miniaturization. *Films also could protect electronic circuits and devices within airplanes from

electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...

interference, which can damage equipment and alter settings. Similarly, such films could allow military aircraft to shield their electromagnetic "signatures", which can be detected via radar. *Buckypaper could act as a filter membrane to trap microparticles in air or fluid. Because the nanotubes in buckypaper are insoluble and can be functionalized with a variety of functional groups, they can selectively remove compounds or can act as a sensor. *Produced in high enough quantities and at an economically viable price, buckypaper composites could serve as an effective armor plating. *Buckypaper can be used to grow biological tissue, such as nerve cells. Buckypaper can be electrified or functionalized to encourage growth of specific types of cells. *The

Poisson's ratio In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Pois ...

for carbon nanotube buckypaper can be controlled and has exhibited

auxetic Auxetics are structures or materials that have a negative Poisson's ratio. When stretched, they become thicker perpendicular to the applied force. This occurs due to their particular internal structure and the way this deforms when the sample i ...

behavior, capable of use as artificial muscles. *Electrode materials for

supercapacitor A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor, with a capacitance value much higher than other capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable ba ...

lithium-ion batteries A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...

, and vanadium redox flow batteries.

References

External links