A Novel Graphene Foam for Low and High Strains and Pressure Sensing Applications
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A Novel Graphene Foam for Low and High Strains and Pressure Sensing Applications Yarjan Abdul Samad, Yuanqing Li and Kin liao Mechanical Engineering Department of Khalifa University of Sci. Tech. & Res. Abu Dhabi 127788, UAE ABSTRACT We are reporting the formation of free-standing graphene foam (GF) via a novel two-step process, in which a polyurethane (PU) foam is first dip-coated with graphene oxide (GO) and subsequently the dried GO-coated-PU is heated in nitrogen atmosphere at 1000qC. During the pyrolysis of the GO-coated-PU, GO is reduced to GF whereas PU is simultaneously decomposed and released completely as volatiles in a step wise mass-loss mechanism. Morphology of the formed GF conforms to that of the pure PU foam as indicated by the scanning electronic micrographs. Polydimethylsiloxane (PDMS) was successfully infiltrated inside the GF to form flexible and stretch-able conductors. The GF-PDMS composite was tested for it’s pressure and strain sensing capabilities. It is shown that a 30% compressive strain changes resistance of the GF-PDMS composite to about 800% of it’s original value. Since density of the formed GF is tunable, therefore, the pressure/strain sensivity of the GF-PDMS composite is also tunable. INTRODUCTION Since the successful realization of two-dimensional (2D) graphene, it has been desired to form a connected, three-dimensional (3D) structure of graphene so as to exploit its extraordinary thermal and electrical properties.[1] 3D graphene structures were first proposed to be formed theoretically and the architectures were simulated for different properties such as enhanced thermal transport and hydrogen storage.[2] Georgios et al. employed the density functional theory (DFT) and proposed the existence of a pillared carbon nanotube (CNT) and graphene structure, combining both in 3D, for enhanced hydrogen storage. Later experimentalists mainly used two methods in order to collect 3D graphene structure.[3] In the first method graphene foams (GFs) are formed using either freeze-drying of graphene oxide (GO), employing a self-assembly chemical process to construct the reduced graphene oxide (rGO) structures in 3D or dip-coating a template.[4-7] The second method is mainly a template-only based technique combined with a chemical vapor deposition (CVD) process where graphene is first deposited on metal/ceramic foam via a CVD process and then the template is etched out completely to form a pure 3D graphene structure.[8-13] These two methods produce GF with entirely different electrical, thermal, morphological, and mechanical properties with different levels of scalability.[14-17] While the latter method produces high quality porous graphene structures, the former is more facile and scalable. In general there are reports on obtaining 3D graphene structures with desired geometry, tunable densities, high electrical conductivity, and scalability to industry level along with suitable mechanical properties; nonetheless, there still is room for conducting complementary work of creating 3D graphene structu
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