Direct Measurements of the Mechanical Strength of Carbon Nanotube–Poly(methyl methacrylate) Interfaces

Abstract

Understanding the interfacial stress transfer between carbon nanotubes (CNTs) and polymer matrices is of great importance to the development of CNT-reinforced polymer nanocomposites. In this paper, an experimental study is presented of the interfacial strength between individual double-walled CNTs and poly(methyl methacrylate) (PMMA) using an in situ nanomechanical single-tube pull-out testing scheme inside a high-resolution electron microscope. By pulling out individual tubes with different embedded lengths, this work reveals the shear lag effect on the nanotube-polymer interface and demonstrates that the effective interfacial load transfer occurs only within a certain embedded length. These results show that the CNT-PMMA interface possesses an interfacial fracture energy within 0.054-0.80 J/m(2) and a maximum interfacial strength within 85-372 MPa. This work is useful to better understand the local stress transfer on nanotube-polymer interfaces.

The mechanical and electrical properties of direct-spun carbon nanotube mat-epoxy composites

“…It is known from fractography [33] that the layer of epoxy surrounding the bundles has a yield strength much above that of the epoxy matrix which fills the voids within the bundle network: Images of the fracture surface of direct-spun CNT mat-epoxy composites reveal that CNT bundles protruding from the fracture surface are coated with this sheath of epoxy. Pull-out tests upon individual CNTs embedded in epoxy reveal that the strength of the epoxy layer which coats CNTs can be over 350 MPa [84,85], even reaching 630 MPa [86]. The epoxy adheres adjacent CNTs within the outer layer of the bundle, and thereby increases the bundle longitudinal shear strength.…”

Fracture toughness of the sidewall fluorinated carbon nanotube-epoxy interface

“…21) and thus comparable to the values reported for nanotube pullout from a polyethylene-butene matrix (4-70 J/m 2 ), 14 pristine graphitized and oxidatively functionalized vapor grown carbon nanofibers from an epoxy matrix (0.65 and 3.3 J/m 2 , respectively) 13 and the double walled CNT-PMMA interface (0.13-0.23 J/m 2 ). 17 The values were still, however, approximately one order of magnitude lower than that for engineered composite materials (16-34 J/m 2 ). 26…”

“…Indirect analysis techniques, such as macro-scale composite specimen testing and strain induced Raman shift measurements, have been found to be extremely convenient and thus commonly used to assess the strength and load transfer efficiency of CNT-matrix interfaces, 1,11,12 although there have been a handful of reports that discuss nanoscale single CNT/CNF pullout. [13][14][15][16][17] Implementation of a single fiber pull-out analysis is considered extremely desirable within the composite science community, since few assumptions need be made when interpreting experimental data and because they provide extremely accurate and reliable results. The single fiber pull-out experiment is a quantitative method for the localized characterization of interfaces and involves the application (and measurement) of a precise load to eject an individual fiber from a matrix.…”

Interfacial Interactions in 1D and 2D Nanostructure-Based Material Systems

“…Therefore, it is of advantage to use small-diameter tubes in exploring their polymer nanocomposites applications. Recently, an innovative single-tube pull-out testing scheme based on in situ electron microscopy nanomechanical characterization techniques is proposed to quantitatively characterize the mechanical strength of interfaces formed by individual DWCNTs (3.1 nm in median diameter) and poly(methyl methacrylate) (PMMA) and epoxy [168,169]. Figure 10.16a illustrates the in situ nanomechanical single-tube pull-out testing scheme inside a SEM chamber.…”