Carbon nanotube yarn, muscle and transparent sheets

Carbon nanotubes
Carbon nanotubes (CNTs) have high strength and modulus, high electrical and thermal conductivities, are stable at relatively high and low temperatures. Individual nanotubes can be 100 times stronger than steel.
To effectively exploit the exceptional properties of individual nanotube’s in various applications, continuous pure CNT yarns and high CNT content composite yarns need to be fabricated.
MWCNTs reinforced PAN fibers and CNT/cellulosic continuous bamboo yarns can be used to manufacture CNTs filled multifunctional products by electro spinning. This process can give significant improvements of the mechanical, thermal and electrical properties of the yarn by incorporation of CNT into the nanofibers. SWCNT fibers can also be manufactured from liquid crystal solutions to get continuous neat CNT fibers.
Making CNT yarn
A continuous CNT fiber yarn using multiple threads of high purity double walled carbon nanotubes can be fabricated in a horizontal CVD gas flow reactor with water vapor densification by the spinning process. Water vapor is used for obtaining homogeneous shrinking of the CNT sock-like assembly with dense thread of thickness 1–3 mm and highly porous structure (99%) with mechanically strong and electrically conductive properties. The CNT yarn can have well controlled continuous winding.  The yarn can be infiltrated with polymers to form a composite and mixed with other yarns to form a blend to be used for various CNT based structural and functional applications.
Artificial muscles made of CNT
Carbon nanotubes can be used to construct artificial muscles as CNTs can be made into yarns which are seamless, hollow cylinders made from the graphite layers.
Researchers claim that the artificial muscles developed by them can provide large, ultra fast contractions to lift weights that are 200 times heavier than possible for a natural muscle of the same size. But at present the artificial muscle is unsuitable for directly replacing muscles in the human body.
Making CNT muscles
The artificial muscles are made by infiltrating a volume-changing paraffin wax into twisted yarn made of carbon nanotubes. Heating the wax-filled yarn, either electrically or using a flash of light, causes the wax to expand, the yarn volume to increase, and the yarn length to contract.
The volume increase of yarn and decrease of length results because of the helical structure produced by twisting the yarn.
Applications of muscles
These yarn muscles are simple and have high performance and muscle contraction or actuation can be ultra fast, occurring in 25-thousandths of a second for both actuation and reversal. They can be used for diverse applications in robots, catheters for minimally invasive surgery, micro motors, and mixers for micro fluidic circuits, tunable optical systems, micro valves, positioners and even toys.
Carbon Nanotube Sheets
There are difficulties in assembling the trillions of nanotubes into macro-sized objects without the use of binders. This aspect has retarded the growth of practical applications.
By simultaneously rotating carbon nanotubes in vertically oriented nanotube arrays (forests) wide and long transparent sheets can be formed. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aero gel that can be densified into strong thin sheets. These nanotube sheets have been used for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes.


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