Direct Observation of Polymer Sheathing in Carbon Nanotube−Polycarbonate Composites

Abstract

A series of observations of polymer sheathing in multiwalled carbon nanotube (MWCNT)−polycarbonate composites are presented. This sheathing was observed in images of the composite fracture surface and is consistent with diameter distributions of the as-received and embedded MWCNTs. A novel nanomanipulation experiment, where the sheathing balls up when contacted by an AFM tip, confirms this phenomenon. This sheathing layer is direct evidence of substantial MWCNT−polymer interaction and will influence the mechanical properties of MWCNTpolymer composites.Due to the outstanding physical properties of carbon nanotubes, intense activity is being devoted to the development of carbon nanotube-polymer composites.1 Specifically, carbon nanotube-reinforced polymer composites have demonstrated high strength and stiffness, 2 which suggest their potential use as alternative materials for structural applications. Multifunctional nanotube-polymer composites are also under development, where in addition to improved mechanical properties, increases in electrical conductivity 3 and improved thermal properties 4 are obtained with small amounts of embedded nanotubes.One of the significant differences between micron-sized carbon fiber-filled polymers and nanotube-filled polymers is the large interfacial area of the nanotubes. This interfacial area provides an opportunity for altering the mobility and properties of a significant volume of polymer near the interface (i.e., the interphase region). Both the interface and interphase regions will play key roles in optimizing load transfer between the nanotube and the polymer matrix. While for traditional composites a variety of experimental techniques have been developed in an effort to quantify the fibermatrix interface, 5 for nanotube-polymer composites these tests are exceedingly difficult because of the small size of the nanotubes. In the process of developing nanoscale pullout tests of individual multiwalled carbon nanotubes from a polymer matrix, we have found several forms of evidence that suggest multiple polymer layers sheath the embedded nanotubes. This polymer sheathing is consistent with models of a nonbulk polymer interphase region that has been identified in nanotube-polymer composite systems. 6 The results presented in this paper are consistent with the findings of other researchers regarding the existence of intimate MWCNT-polymer interaction in nanotubepolymer composites. For example, strong polymer adherence has been reported in previous TEM studies of nanotubepolymer nanocomposite samples.7 Potschke et al. studied the rheological behavior of nanotube-polycarbonate composites, and their SEM observation of the fracture surface showed that the apparent nanotube diameters at the fracture surface were larger than the diameters of the original carbon nanotube material, indicating significant polymer wetting on the nanotube surface. 8 However, to date a detailed study of this polymer sheathing phenomenon in carbon nanotubepolymer nanocomposites has not been undertaken. ...

Graphitic nanofillers in PMMA nanocomposites—An investigation of particle size and dispersion and their influence on nanocomposite properties

“…Similar adhesion of polymer to carbon nanotubes during fracture pull-out was observed for MWNTs in polycarbonate. [53][54][55][56][57] The improved dispersion and adhesion of the PMMA to GNPs may be attributed to the modestly higher surface area, decreased crystallite size and greater surface roughness through the nanopores observed in the nanofiller (Fig. 2).…”

Visualization of the conductive paths in injection moulded MWNT/polycarbonate nanocomposites by conductive AFM

“…Features of CNTs such as excellent mechanical properties, electrical and thermal conductivity associated with their high aspect ratio and low density, have several potential benefits which are expected to manifest when they are employed as fillers in polymers [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…The CCI method is based on the fact that in case of certain SEM imaging conditions the nanotubes connected to electrical percolation paths, have different contrast to nanotubes not connected to it [20]. A. Noll and T. Burkhart characterized the electrical conductivity of multiwall carbon nanotubes poly(p-phenilene sulphide) composite using CCI of a low acceleration voltage SEM, revealing the electrical properties of the studied composite [18,19].…”

Role of atomic scale interfaces in the compressive behavior of carbon nanotubes in composites

“…In the case of carbon nanotubes, there are conflicting reports regarding the strength of interfaces. Several researchers report evidence for load transfer based on microstructural and spectroscopic observations [9,[23][24][25]. Ding and coworkers [25] have observed polymer sheathing of nanotubes in PMMAnanotube composite indicating strong interaction between nanotubes and PMMA.…”

“…Several researchers report evidence for load transfer based on microstructural and spectroscopic observations [9,[23][24][25]. Ding and coworkers [25] have observed polymer sheathing of nanotubes in PMMAnanotube composite indicating strong interaction between nanotubes and PMMA. Some investigators report low interfacial load transfer [14,26].…”