Abstract
Incorporating nanofillers into elastomers leads to composites with an enormous potential regarding their properties. Unfortunately, nanofillers tend to form agglomerates inhibiting adequate filler dispersion. Therefore, different carbon nanotube (CNT) pretreatment methods were analyzed in this study to enhance the filler dispersion in polydimethylsiloxane (PDMS)/CNT-composites. By pre-dispersing CNTs in solvents an increase in electrical conductivity could be observed within the sequence of tetrahydrofuran (THF) > acetone > chloroform. Optimization of the pre-dispersion step results in an AC conductivity of 3.2 × 10−4 S/cm at 1 Hz and 0.5 wt.% of CNTs and the electrical percolation threshold is decreased to 0.1 wt.% of CNTs. Optimum parameters imply the use of an ultrasonic finger for 60 min in THF. However, solvent residues cause a softening effect deteriorating the mechanical performance of these composites. Concerning the pretreatment of CNTs by physical functionalization, the use of surfactants (sodium dodecylbenzenesulfonate (SDBS) and polyoxyethylene lauryl ether (“Brij35”)) leads to no improvement, neither in electrical conductivity nor in mechanical properties. Chemical functionalization enhances the compatibility of PDMS and CNT but damages the carbon nanotubes due to the oxidation process so that the improvement in conductivity and reinforcement is superimposed by the CNT damage even for mild oxidation conditions.
Highlights
Elastomer-composites consist of a crosslinked rubber matrix and several additives to reach the performance needs and to fulfill processing, technical, and economical requirements
As an appropriate pre-dispersion step enables to break up carbon nanotube (CNT) agglomerates due to
As an appropriate pre-dispersion step enables to break up CNT agglomerates due the decrease of particle–particle interactions, different pre-dispersion approaches were to the decrease of particle–particle interactions, different pre-dispersion approaches were investigated in this study
Summary
Elastomer-composites consist of a crosslinked rubber matrix and several additives to reach the performance needs and to fulfill processing, technical, and economical requirements. CNTs consist of rolled up graphene sheets leading to a high specific surface area and a high aspect ratio [1] implying improvements regarding the reinforcement of elastomers. This has been proven successfully for several times [2,3,4,5,6,7]. Nanofillers exhibit high particle–particle interactions due to van der Waals forces and tend to form agglomerates [9,10] It is challenging when incorporating CNTs into a polymer matrix as the agglomeration behavior hinders the formation of a homogeneous filler dispersion in the polymer matrix. To take benefit of the enormous potential of carbon nanotubes it is inevitable to break up the agglomerates to disperse the carbon nanotubes adequately and to offer a high contact surface area for optimal polymer–filler interactions
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