Highly sensitive nanofiber-embedded touchscreens

(Nanowerk News) Flexible touchscreen panels (TSPs) are part of many modern electronic devices. Among diverse touch-sensing methods, the capacitive TSP has practically dominated the market due to its multitouch functionality.
Since most wearable electronic devices such as smartphones and watches can suffer from daily wear and tear, they need to have a protective layer. Currently this is provided by a thin layer of glass (such as gorilla glas) on top of the TSP.
However, with flexible electronics on the horizon, TSPs can no longer use glass because of its fragility, and the inevitable result has been the use of plastic films as the cover layers for flexible TSPs. Unfortunately, commercial transparent plastic films have relatively low dielectric constants (k between 2 and 4 – dielectric constants (k) are important for high touch sensitivities) and modest mechanical properties. That makes them unsuitable for use with flexible TSPs that must have high sensitivity and outstanding durability.
Researchers in Korea now have demonstrated the fabrication of transparent and flexible cellulose nanofiber (CNF) films with high k values by incorporating ultralong metal nanofibers.
In a paper in Advanced Materials ("High Dielectric Performances of Flexible and Transparent Cellulose Hybrid Films Controlled by Multidimensional Metal Nanostructures"), they report an unconventional approach for forming flexible and transparent cellulose nanofiber films.
Preparation of ultralong silver nanofibers
Preparation of ultralong silver nanofibers (AgNFs). a) Schematic illustration of the fabrication process for the ultralong AgNF solution. Optical images of cracked PVP sacrificial layer and disconnected AgNFs according to stretching rate of b) 12.5, c) 25, d) 37.5, e) 50 cm s-1, respectively. f) AgNF length as a function of stretching rate. The red solid line represents the linear relationship between fiber length and stretching rate. Scale bars are 100 µm. (© Wiley-VCH Verlag) (click on image to enlarge)
The team produced aligned arrays of these metal nanofibers continuously by electrospinning a suspension of metal nanoparticles onto a rotating drum collector, and their lengths were controlled by a stretching method for cracking these aligned fibers.
Embedding these metal nanofibers into cellulose hybrid films resulted in transparent films with significantly high k values (above 12.9), compared to the k values of conventional glasses.
Also, the remarkable mechanical and thermal stabilities of the cellulose hybrid films made them suitable for use as the protective cover layers of flexible and sensitive TSPs in wearable electronic devices that are exposed to diverse outdoor activities.
"We believe this approach provides a promising strategy for next-generation, wearable electronics," the authors conclude.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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