Severe graphene nanoplatelets aggregation as building block for the preparation of negative temperature coefficient and healable silicone rubber composites

Abstract

With the request of higher performance in automotive products, sealing components and materials resisting to severe conditions, the performance requirements for silicones are becoming ever more diverse and sophisticated. In this article we prepared silicone rubber (SR)-graphene nanoplatelets (GNPs) composite via liquid mixing method; the mechanical strength of the GNPs estimated by applying quantized fracture mechanics suggested a severe GNPs agglomeration that was confirmed by scanning electron microscopy analysis. We observe that such SR/GNP composite behaves as a negative temperature coefficient material, exhibiting electrical resistance decrease with temperature increase. It was also shown how the damaged SR/GNP composite can be healed by simple thermal annealing. The healing mechanism was rationalized in terms of "living" reactive species that are not consumed by curing at room temperature and promote, when thermally activated, the crosslinking among the damaged network of oligomers. The healing efficiency, expressed as crack length vs. annealing temperature, has been estimated again applying the principles of quantized fracture mechanics. These results could satisfy many of the demanding requirements of the silicone rubber materials used in daily life and indicate that SR/GNP composites can act as healable and temperature sensor materials e. g. for seals, hoses and automotive sector.

Recent Achievements of Self-Healing Graphene/Polymer Composites

“…The simple mixing is the simplest and commonest method for preparing graphene or graphene derivative/polymer composites [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. Usually, graphene or graphene derivatives are blended with polymers by mechanical mixing or ultrasonic dispersion.…”

Nanocarbon Reinforced Rubber Nanocomposites: Detailed Insights about Mechanical, Dynamical Mechanical Properties, Payne, and Mullin Effects

“…Despite several advantages, the vulcanized neat silicone rubbers usually have poor mechanical properties and low thermal/electrical conductivity restricting its use in many industrial applications. Therefore, silicon rubber filled with carbon based nanofillers have been reported [ 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 197 , 198 , 199 , 200 ]. Room temperature vulcanized (RTV) vulcanizates on adding 2 phr of CNTs increased the Young’s modulus by 272% and reached as high as ~706% at 8 phr [ 116 ].…”

“…Such enhancements in mechanical properties of the nanocomposites are attributed to the homogeneous dispersion of silicone-g-MWCNTs in the silicone elastomer matrix. In addition, graphene [ 135 , 136 , 137 , 139 , 140 , 197 ] and graphene oxide [ 198 , 199 , 200 ] has been incorporated to enhance the mechanical properties of the silicone rubber. Mechanical property measurements of liquid silicone rubber/GO functionalized with triethoxyvinylsilane composites (0.3 wt %) displayed a 2.3-fold increase in tensile strength, 2.79-fold enhancement in tear strength, and 1.97-fold reinforcement in shear strength when compared with the neat liquid silicone rubber [ 199 ].…”

Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al2O3 Particles

“…It is composed of a linear Si-O-Si moiety with a bond-angle between 104 • and 180 • , which introduces flexibility to the polymer [11,12]. In addition, polysiloxane can be used permanently without any change at 150 • C, it is able to withstand 200 • C for 1000 h, and 350 • C for shorter periods of time [13,14]. However, some studies on the long-term reliability of silicone rubber suggest that commercial high-temperature silicones, which are being aged at 250 • C could suffer from severe thermal decomposition [15][16][17].…”