3 novembre 2020

[Nanotubes] – How Carbon Nanotubes Could Lead the Way in Next-Generation Smart Fabrics

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A growing demand for smart fabrics in different fields that not only serves traditional requirements of protection, safety, fashion, and convenience but also can adjust themselves according to the exterior environment has encouraged textile industries to work on next-generation smart fabrics.

What are Next-Generation Smart Fabrics?
First introduced in the early 1990s (Libertino, Plutino, & Rosace, 2018), smart fabrics are designed to add value to the conventional textiles by including communication, transformation and energy conduction that respond to the outside-the-body environment, as in keeping us warm in cold climates and cool in hot environments (Gaddis, 2014).

The medical field has already considered smart fabrics as a process to monitor body temperature, heart rate, or other vital signs and gives warnings of potential health conditions (Chandler, 2020). Smart fabrics are classified into three types according to their functionality (Mikhalchuk, 2017):

First-generation: Passive smart fabrics, consisting of sensors that can gather information about the surrounding environment
Second-generation: Active smart fabrics that consist of both sensors and actuators, and can memorize the shape, control temperature, and the heat of the fabric
Third-generation: An advanced ultra-smart fabrics, which works like a small built-in computer that can sense and interpret distinct data types, and make the materials fit the external conditions.
Materials used for Smart Fabrics
Many researchers are currently researching and developing composite materials for next-generation smart fabrics.
Formerly, the conductive fabrics have been made by wrapping fibers in fine metallic wire or applying adhesive circuits onto the surface (Ellis, 2019). However, their main drawbacks are not being able to be washed at high temperatures and their lack of stretchability.
In 2018, a British start-up company, Pireta (Moreton, 2018) introduced a solution for these problems that involved coating each fiber with a 2 nm thick layer of copper directly to any fabric of various kinds, such as woven or non-woven, natural or synthetic. They managed to keep the fabrics’ original breathable and stretchable characteristics.
Recent research (Chatterjee, Negi, Kim, Liu, & Ghosh, 2020) claims that a film made up of tiny carbon nanotubes shows extraordinary thermal, electrical, and physical properties that make this nanomaterial an appealing candidate for next-generation smart fabrics.

What are Carbon Nanotubes (CNTs)?
Quasi-one-dimensional CNTs are cylindrical molecules that consist of rolled-up sheets of single-layer graphene. They can be single-walled (SWCNTs) with a diameter of less than 1 nm or multi-walled (MWCNTs), with diameters reaching up to or more than 100 nm.
The covalently bonded carbon atoms through sp2 molecular orbitals with the fourth free valence electron that is highly mobile is available to give them their properties of high conductivity and high strength (Lekawa‐Raus, Patmore, Kurzepa, Bulmer, & Koziol, 2014).
Although MWCNTs have the same level of conductivity as metals, SWCNTs could be conductors, semi-conductors, or non-conductors depending on whether they are armchair, zigzag or chiral vectors (Berger, n.d).
CNTs are believed to have 400 times the mechanical tensile strength of steel, and a superior thermal conductivity to diamonds. They are also chemically stable and resist any chemical impact unless exposed to high temperature and oxygen. These desirable properties make the CNTs an ideal candidate for many applications, such as in smart fabrics.Role of Carbon Nanotubes in Next-Generation Smart Fabrics
Very light-weight CNTs with their unique electrical, thermal, and mechanical properties give them the ability to blend themselves in the development of new composite materials in the field of smart fabric technology. This makes them a primary choice in the development of ultra-thin sensors and electronic components (Libertino, Plutino, & Rosace, 2018).
A research team (Doshi & Thostenson, 2018) at the University of Delaware has demonstrated next-generation smart textiles using CNTs composite coatings on a wide range of fibers, including cotton, nylon and wool. The sensor prepared with this coating could be easily slipped into the soles of shoes, or stitched into clothing for detecting electrical changes during human motion.
Future of Next-Generation Smart Fabrics
Users of next-generation fabrics require flexibility, stability, simplicity, non-toxic elements and low costs, with efficient heating and cooling features.
Scientists have proven that CNTs could be a potentially affordable thermoelectric material that would absorb heat away or towards the body when an external source of current is applied. These outstanding properties of the material could contribute to further research in creating a very useful energy harvesting capability, additionally opening the door to new fabric-based conductive textiles in the broader market.

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