Fabrication and Nanocompression Testing of Aligned Carbon‐Nanotube–Polymer Nanocomposites

Abstract

The exceptional electronic, thermal, and mechanical properties of carbon nanotubes (CNTs) have motivated extensive research on their manufacturing and applications. At bulk scales, there is particular interest in property enhancements by adding CNTs to polymers to make composite materials. Most work on CNT-based composites presented in the literature to date has focused on dispersion of single-or multiwalled CNTs (SWNTs or MWNTs) in the matrix; however, bulk CNTs embedded in a polymeric matrix tend to form aggregates that are not only poorly adhered to the matrix but also concentrate stresses, compromising the effect of the CNTs as reinforcement.[1] On the other hand, establishing order and alignment among CNTs within a composite matrix offers significant further potential to harness the properties of individual CNTs at bulk scales by realizing the anisotropic properties of CNTs in desired directions, and by enabling packing and dispersion of CNTs at much higher volume fractions than in tangled configurations. In this work, CNT-polymer composites are manufactured by wetting as-grown arrays of vertically aligned CNTs rapidly and effectively (lack of voids) using off-the-shelf polymers. The wetting process not only preserves the alignment of the CNTs, but also allows the controlled manufacturing of nanocomposite test structures. Direct characterization of the mechanical properties of the nanocomposite structures is also presented in this work. The mechanical-reinforcement results support the feasibility of using these CNT arrays in large-scale hybrid advanced composite architectures reinforced with aligned CNTs. Such composites will also benefit from multifunctional property (e.g., electrical conductivity) enhancements owing to the aligned CNTs.The mechanical properties (e.g., Young's modulus, hardness) of thin films containing randomly oriented CNTs inside a polymer matrix have been assessed using various techniques, that is, analytical models, [2][3][4][5] standard tension and compression tests, [6][7][8][9][10] and nanoindentation techniques. [11][12][13][14][15] The composite modulus along the CNT axis (stiff axis) of well-aligned CNT-polymer composites has not been studied to date. In the most relevant related work, Fang et al. [16] usedBerkovich nanoindentation to determine the hardness of chemical vapor deposition (CVD)-grown aligned MWNTparylene nanocomposites, but did not report their modulus. Parylene is a gas-phase deposited polymer typically used for electrical isolation. Modulus characterization in the transverse direction (i.e., CNTs aligned perpendicular to the direction of modulus measurement) indirectly inferred from structural tests was reported, with a significant increase (by a factor of 20-30) over the assumed modulus of parylene. Modulus characterization using direct measurement methods, not dependent on structural models, is preferred when available. The present work is the first to characterize the mechanical properties of well-aligned CNT-epoxy nanocomposites along the CNT axis using direct...

Epoxy resin nanocomposites reinforced with ionized liquid stabilized carbon nanotubes

“…With CNTs having become commercially available in recent years, more effort from both academic and industrial communities has been put toward their applications. In fact, the CNTs have realized their first real application in terms of the CNTs-based nanostructural and functional materials [5][6][7]. CNT/polymer nanocomposites have been pursued with the aim of delivering the properties of the CNTs to the hosting polymer matrix [8][9][10].…”

Three-dimensional elastic constitutive relations of aligned carbon nanotube architectures

“…However, due to the limitations of sample size and testing techniques, which commonly include either bulk compression or nanoindentation, [18][19][20] previous studies were not able to determine the full constitutive relations for such materials. 18,20 Using uniaxial tensile tests, we quantify the mechanical behavior of high V f (up to ∼ 20 vol. %) aligned CNT (A-CNT) architectures along the longitudinal, transverse, and shear directions, and develop the first full set of elastic constitutive relations for an A-PNC material.…”

“…1,2, 8,[11][12][13][14][15][16][17] To take full advantage of the anisotropic properties, a number of recent studies focused on the integration of aligned carbon nanotubes (CNTs) at a variety of CNT volume fractions (V f ) into a polymer matrix architecture, [18][19][20][21][22] forming an aligned CNT polymer nanocomposite (A-PNC). However, due to the limitations of sample size and testing techniques, which commonly include either bulk compression or nanoindentation, [18][19][20] previous studies were not able to determine the full constitutive relations for such materials.…”

Epoxy-based Carbon Nanotubes Reinforced Composites

“…Above the 0.3 wt%, CNTs agglomerated. In another report, García and co-workers [García et al, 2007] manufactured epoxy nanocomposites by wetting as-grown arrays of vertically grown CNTs (synthesized by CVD) by the submersion method. Two grades of SU-8 UV-curing thermoset epoxy (Microchem 2000.1 and 2025) were selected to prepare the composites.…”

“…The properties decreased at higher amount of CNTs. Garcia and co-workers [García et al, 2007] used dimensions measured from SEM images to predict the Young's modulus of a vertically aligned (VA) CNT array-epoxy composite. The Young's modulus increased from 3.7 to 12 GPa, and the reinforcement for the CNT pillars was 220%, showing effective reinforcement.…”