Junction-Controlled Elasticity of Single-Walled Carbon Nanotube Dispersions in Acrylic Copolymer Gels and Solutions

Abstract

Oscillatory shear rheometry is used to study the mechanical response of single-walled carbon nanotubes dispersed in solutions of acrylic diblock or triblock copolymers in 2-ethyl-1-hexanol. Thermal transitions in the copolymer solutions provide a route for the easy processing of these composite materials, with excellent dispersion of the nanotubes as verified by near-infrared photoluminescence spectroscopy. The nanotube dispersions form elastic networks with properties that are controlled by the junction points between nanotubes, featuring a temperature-dependent elastic response that is controlled by the dynamic properties of the matrix copolymer solution. The data are consistent with the formation of micelle-like aggregates around the nanotubes. At low temperatures the core-forming poly(methyl methacrylate) blocks are glassy, and the overall mechanical response of the composite does not evolve with time. At higher temperatures the enhanced mobility of the core-forming blocks enables the junctions to achieve more intimate nanotube−nanotube contact, and the composite modulus increases with time. These aging effects are observed in both diblock and triblock copolymer solutions but are partially reversed in the triblock solutions by cooling through the gel transition of the triblock copolymer. This result is attributed to the generation of internal stresses during gelation and the ability of these stresses to break or weaken the nanotube junctions.

Effect of graphene on the self-assembly and rheological behavior of a triblock copolymer gel

“…5 The Table 1 The values of fitted parameters to fit the experimental stressrelaxation data shown in Fig. Next, we try to hypothesize the location of graphene nanoplatelets in the gel.…”

“…Selecting nanoparticles with desired functionalities and then incorporating these nanoparticles in polymer gels can potentially result in materials with novel and interesting properties. [4][5][6][7] A typical polymer gel consists of two phases, polymer and solvent. The nanoparticles can have different affinities to these phases and can preferentially interact with one of these phases.…”

Nanoparticles as macromolecules

“… Block copolymers, including pluronics, have also been used with some success. Wrapping polymers such as single‐stranded DNA and certain aromatic polymers can also be effective dispersants, and SWCNTs have recently been stably sequestered in self‐assembled aqueous nanopores. Chemical functionalization is an alternative route to dispersion, although disruption of the pristine graphene lattice with what amounts to a chemical defect can have a significant effect on the optical and electronic properties of the nanotubes.…”

Length‐Dependent Mechanics of Carbon‐Nanotube Networks

“…CNT networks enhance the strength, [5,6] conductivity, [7][8][9] and flame resistance [10] of polymer composites, and have a spectacular effect on the rheology of CNT suspensions. [11][12][13][14][15][16][17] With recent progress in the ability to control CNT length, aspect ratio, defined as the ratio L/d, where L is nanotube length and d is diameter, has emerged as a key parameter in determining CNT percolation, [6,7] optical response, [18] toxicity, [19,20] and flow alignment. [21,22] Although in most commercial applications the network forming attributes of CNTs are critical, the influence of aspect ratio on the mechanics of such networks has received only limited attention.…”