Abstract
Flexible optoelectronic technologies are becoming increasingly important with the advent of concepts such as smart-built environments and wearable systems, where they have found applications in displays, sensing, healthcare, and energy harvesting. Parallelly, there is also a need to make these innovations environmentally sustainable by design. In the present work, we employ nanocellulose and its excellent film-forming properties as a basis to develop a green flexible photonic device for sensing applications. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were used as matrix materials along with a black thermochromic pigment to prepare thermoresponsive hybrid films. Optical properties of nanocellulose films such as transparency and haze were tuned by varying pigment loading. Nearly 90% transparent CNF and CNC films could be tuned to reduce the transmission to as low as 4 and 17%, respectively. However, the films regained transparency to up to 60% when heated above the thermochromic transition temperature (31 °C). The thermoresponsive behavior of the prepared films was exploited to demonstrate an all-optical modulation device. Continuous infrared light (1300 nm) was modulated by using a 660 nm visible diode laser. The laser intensity was sufficient to cause a localized thermochromic transition in the films. The laser was pulsed at 0.3 Hz and a uniform cyclic modulation depth of 0.3 dB was achieved. The demonstrated application of functional nanocellulose hybrid films as a light switch (modulator) could be harnessed in various thermally stimulated sensing systems such as temperature monitoring, energy-saving, and anti-counterfeiting.
Highlights
The demand for flexible electronic and photonic technologies is arising with the introduction of revolutionary concepts such as smart-built environments and wearable systems
Two different types of nanocellulose hybrid films were prepared in this present work using Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) as matrix materials, in order to study the effect of morphology on the formation of hybrid film structures
Both nanocellulose materials were doped with a leuco dye-based thermochromic pigment at four different addition levels, viz., 5, 10, 20, and 30% based on dry cellulose mass
Summary
The demand for flexible electronic and photonic technologies is arising with the introduction of revolutionary concepts such as smart-built environments and wearable systems. Flexible optoelectronics typically utilizes ultrathin glass, metal foil, and various plastics, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), poly-dimethyl siloxane (PDMS), and polyimides (PI), as substrates.[2−4] These materials are typically used as passive substrates having no active role in the applications. Post usage, these plastics can cause serious environmental concerns due to their nonbiodegradable nature and the resulting accumulation in the environment, referred to as “white pollution”.5. There is a pressing need for renewably sourced (biobased) and biodegradable material alternatives, which can match the performance of conventional materials in optoelectronics applications
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