High Interfacial Shear Strain in Polyurea–Carbon Nanotube Composite Sheets

Abstract

One of the factors limiting the performance of polymer–carbon nanotube (polymer–CNT) composites is the insufficient load transfer across their interface. In this study, interfacial strain in polyurea–CNT systems with two types of CNT sheet has been studied. These are (a) as manufactured CNT sheets (termed unbaked CNT sheets) containing amorphous carbon and (b) thermally treated CNT sheets (termed baked CNT sheets) with amorphous carbon eliminated. The process of baking not only eliminates amorphous carbon but also creates chemically active defects in CNTs as well as sp3 carbon. These factors serve to enhance interfacial strain in the polyurea–CNT system. The shift in the Raman G′ band, while the sheets were mechanically strained, has been used to estimate the polyurea–CNT interfacial strain. The maximum Raman G′ downshift in the range of 33–39 cm–1 has been observed in composites of baked CNT sheets with 53 wt % polyurea. This is more than a factor of 2 higher than the downshift reported for any polymer–CNT system to date and represents a local CNT strain of ∼0.9–1% or a local CNT stress of 9–10 GPa. This study opens a window toward achieving the mechanical properties potential of bulk polymer nanocomposite for applications including, but not limited to, structural materials.

The effects of processing and carbon nanotube type on the impact strength of aerospace‐grade bismaleimide based nanocomposites

“…To investigate the cause of the reduced impact strength in the nanocomposites, we first used Raman spectroscopy to examine any cure-induced stresses (tension or compression) in the CNT A (Figure 3). Raman spectroscopy has been employed in prior studies [60,61] for evaluating the tensile stress at the polymer-CNT interface, where the polymer-nanocomposites were stretched under a Raman spectroscope and their Raman spectra collected. The tensile strain in the CNTs results in a downshift of the Raman band frequencies (D $ 1300 cm À1 , G $ 1580 À1 , and G 0 $ 2600 À1 ) due to the weakening of C═C bonds.…”

Cure Behavior Changes and Compression of Carbon Nanotubes in Aerospace Grade Bismaleimide-Carbon Nanotube Sheet Nanocomposites

“…In our prior work using UB and B CNTs, the B CNT and its nanocomposite with polyurea demonstrated two additional WAXD peaks at ∼30 and 35.5° 2θ which were not observed in the UB CNT and its nanocomposite with polyurea. The X-ray photoelectron spectroscopy (XPS) results signified an absence of any “foreign particle”, i.e., a catalyst or an impurity in the B CNTs, to which the additional XRD peaks could be assigned to . The Raman I D / I G of the B CNT was ∼2× that of the UB CNT, signifying that the baking treatment created defects in the CNTs .…”

“…Next, we explored the effect of the cure of BMI on the CNTs within the nanocomposite. Raman spectroscopy has been used in prior studies for evaluating the tensile , or compressive stress , on the CNTs in the nanocomposites. In our prior work, CNTs were radially and axially compressed upon the cure of BMI in the nanocomposites containing 0.1 wt % pristine or functionalized CNTs.…”

“…Prior studies in the literature on the CNT-BMI nanocomposites which have used the solution assisted infiltration process, have relied on rapid evaporation of the solvent post infiltration through heating and/or using vacuum. ,,,, To understand the effect that the varying CNT content in different nanocomposites have on the inter-CNT spacing and how that could be critical for understanding the effects on the cure reactions and on the thermomechanical properties in BMI nanocomposites, an ideal CNT-polymer model has been employed. Two different kinds of CNT sheets have been used to prepare the nanocomposites, one containing amorphous carbon (termed as UB CNT) and another where the UB CNT are thermally treated to eliminate the amorphous carbon (termed as B CNT) . More details on the UB and B CNT sheets can be found in our prior work …”

New Insights into Segmental Packing, Chain Dynamics and Thermomechanical Performance of Aliphatic Polyurea Composites: Comparison between Silica Oxides and Titanium (III) Oxides

“…This is important so that it opens an avenue for PU to be employed in newer applications including heat dissipating coatings in printed circuit boards, [31] shock absorbers in fuel cells, [32] and antireflective coatings in PV cells. [33] A wide variety of fillers have been integrated into PU matrix in the past like carbon nanotubes, [34][35][36] carbon black, [37,38] nanoclays, [39,40] glass fibers, [13,41] and graphenes. [42][43][44] However, the studies on metal oxide or metalloid oxides including zinc oxide, titanium-based oxides (TiO, TiO 2 , or Ti 2 O 3 ), or silica oxides-based PU composites, to our best knowledge, are limited.…”