Abstract
While the green production and application of 2D functional nanomaterials, such as graphene flakes, in films for stretchable and wearable technologies is a promising platform for advanced technologies, there are still challenges involved in the processing of the deposited material to improve properties such as electrical conductivity. In applications such as wearable biomedical and flexible energy devices, the widely used flexible and stretchable substrate materials are incompatible with high-temperature processing traditionally employed to improve the electrical properties, which necessitates alternative manufacturing approaches and new steps for enhancing the film functionality. We hypothesize that a mechanical stimulus, in the form of substrate straining, may provide such a low-energy approach for modifying deposited film properties through increased flake packing and reorientation. To this end, graphene flakes were exfoliated using an unexplored combination of ethanol and cellulose acetate butyrate for morphological and percolative electrical characterization prior to application on polydimethylsiloxane (PDMS) substrates as a flexible and stretchable electrically conductive platform. The deposited percolative free-standing films on PDMS were characterized via in situ resistance strain monitoring and surface morphology measurements over numerous strain cycles, with parameters extracted describing the dynamic modulation of the film’s electrical properties. A reduction in the film resistance and strain gauge factor was found to correlate with the surface roughness and densification of a sample’s (sub)surface and the applied strain. High surface roughness samples exhibited enhanced reduction in resistance as well as increased sensitivity to strain compared to samples with low surface roughness, corresponding to surface smoothing, which is related to the dynamic settling of graphene flakes on the substrate surface. This procedure of incorporating strain as a mechanical stimulus may find application as a manufacturing tool/step for the routine fabrication of stretchable and wearable devices, as a low energy and compatible approach, for enhancing the properties of such devices for either high sensitivity or low sensitivity of electrical resistance to substrate strain.
Highlights
Green and flexible electronic technologies are attracting an ever-increasing amount of attention as an alternative for current rigid technologies due to their potential for realizing unique form factors, multifunctionality, improved sustainability, and greater conformability for incorporation into applications such as optoelectronics, soft robotics, and biomonitoring.[1−3] The utilization of graphene as an active component in these next-generation technologies provides an additional improvement, given the high theoretical electrical and thermal conductivities of this material.[4]
We focus on the following: first, exfoliation of graphene flakes in EtOH with the assistance of cellulose acetate butyrate (CAB) is demonstrated as a green approach
Thermogravimetric analysis (TGA) was employed to quantify the polymeric residue, which was estimated at ∼5 wt % for the final 2 h exfoliated material and at ∼10 wt % for the 4 h liquid-phase exfoliation (LPE) process
Summary
Green and flexible electronic technologies are attracting an ever-increasing amount of attention as an alternative for current rigid technologies due to their potential for realizing unique form factors, multifunctionality, improved sustainability, and greater conformability for incorporation into applications such as optoelectronics, soft robotics, and biomonitoring.[1−3] The utilization of graphene as an active component in these next-generation technologies provides an additional improvement, given the high theoretical electrical and thermal conductivities of this material.[4]. Rigid substrates, a high-temperature annealing step is often required to reduce the presence of insulating elements such as residual adsorbed solvents and polymers/other non-functional components.[14,15] In contrast, flexible substrates and stretchable platforms are not readily compatible with such thermal processing, as the structural stability of these substrate materials is compromised due to decomposition and increased stiffening at relatively high temperatures This thermal limitation requires the application of high but concentrated energy alternatives such as focused laser annealing and rapid photonic annealing to reduce the electrical resistivity.[11,16,17] alternative low-energy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
