Graphene and Carbon Nanotube Auxetic Rubber Bionic Composites with Negative Variation of the Electrical Resistance and Comparison with Their Nonbionic Counterparts

Abstract

Microorganism metabolic activity can facilitate the formation of cellular material systems that have unusual mechanical and physical properties. In the living world microorganisms are commonly used for preparing porous food by fermentation; here carbon nanotubes, graphene nanoplatelets, and a mix of them are dispersed in liquid silicone rubber with single-cell fungi of commercial beer yeast. The fermentation of such microorganisms during the gelling of the silicone matrix results in bionic composites with buckled/collapsed cells that infer, as rationalized with an analytical model and excluded in a abiotic experimental comparison, auxetic properties. During stretching it is found that the Poisson's ratio of such composites changes sign, from negative to positive, and the variation of the electrical resistance is negative. In addition to the conductivity increment, a general increment of the stretchability and damage resistance with respect to the composites prepared by abiotic process is observed. Bionic composites, even if in their infancy, can thus be multifunctional and superior to their traditional/abiotic counterparts.

Engineered Living Materials: Prospects and Challenges for Using Biological Systems to Direct the Assembly of Smart Materials

“…In these bionic materials, both the living cells and the carbon materials contribute synergistically to the final properties of the materials. Finally, a recent example of a graphene, CNT, and liquid rubber composite produced through yeast fermentation was reported . CO 2 bubbles produced during fermentation along with collapsed yeast cells resulted in the transformation of conventional silicone rubber composites to auxetic robust rubber.…”

Bionicomposites

“…In the case of graphene sheets the bionic composite showed again a higher failure strength, and was able to self-repair after placing the composite material containing living yeast cells back into growth medium. 9 Finally, a recent example of a graphene, CNT, and liquid rubber composite produced through yeast fermentation was reported: 38 Poisson's ratio (i.e., the so called auxetic behavior) that will contract (expand) in the transverse direction when compressed (stretched). 39 Such materials may find in perspective practical applications; for example, once infiltrated in a cavity with a smaller dimension auxetic materials can be used as swell tools that expand by means of tensile stress to conform to the wellbore and to remain anchored to it.…”

Rubber Nanocomposites for Extreme Environments: Critics and Counterintuitive Solutions

“…Recently, the synergistic properties of NBR/CNTs/GNPs and ethylene-propylene-diene terpolymer rubber/carbon black/GNPs nanocomposites have been explored (Valentini et al, 2016(Valentini et al, , 2017(Valentini et al, , 2018. It was found that the combined effect of CNTs/GNPs hybrid filler, exhibited astonishing improvements in terms of mechanical properties, barrier properties, and thermal conductivity.…”

“…Rubber-like materials are those that once compressed along an axis expand in directions orthogonal to the applied load (e.g., positive Poisson's ratio) being the Poisson's ratio values for the majority of them about 0.5. Designed mechanical instabilities on soft materials have been used to realize materials with a negative Poisson's ratio (i.e., the so called auxetic behavior) that will contract (expand) in the transverse direction when compressed (stretched) (Bertoldi et al, 2010;Valentini et al, 2017). Such materials may find in perspective practical applications; for example, once infiltrated in a cavity with a smaller dimension auxetic materials can be used as swell tools that expand by means of tensile stress to conform to the wellbore and to remain anchored to it (Mody et al, 2013).…”