Multiscale Structures in Polymers and nanocompositesSanjeeva N. Murthy, University of Vermont & State Agricultural College, DMR 0513926

The increased modulus of nanotube-reinforced polyacrylonitrile (PAN) fibers was investigated by deforming single 20-100 m dia. filaments in an x-ray beam at the Argonne Photon Source. Data (Fig.1a) showed that nanotubes deform and contribute to the modulus. PAN chains were laterally compressed during elongation and underwent conformational changes from helix to zigzag (Fig. 1b). These changes were reversible even near the breaking strain (Fig. 1c) [W. Wang, N.S. Murthy, H.G. Chae and S. Kumar; Polymer 49, 2133-2145 (2008)].

Mechanical adhesion between the fibers and a matrix in composites was dramatically enhanced by micrometer-sized surface corrugations generated on the fiber surfaces by laser ablation. Symmetric and asymmetric corrugations were produced by irradiating Kevlar® fibers with high-fluence UV laser pulses (Fig. 2). The interfacial shear strength between the fibers and the matrix, measured using the microbond fiber-pullout, increased by 120% with symmetric corrugation profiles obtained with laser irradiation normal to the fiber-axis, and 5-fold with asymmetric corrugation profiles obtained with the laser incidence angle of 45 to the fiber axis [ F. Bédoui, N. S. Murthy and F. M. Zimmermann, J. Mat. Sci. (2008)].

Figure 1. (a) 2D X-ray diffraction pattern from PAN. (b) Overlay of a sequence of meridional 1D scans calculated from a 2D image of a PAN/MWNT composite fiber; S is the scan at start of the deformation, and F is after failure. Z is the peak due zigzag chains and H is the peak due to helical chains. (c) Changes in the axial strain, lateral strain and zigzag fraction through two loading and unloading cycles followed by strain to failure.

Figure 2. Scanning-electron micrographs of laser-ablated Kevlar fibers. Laser is incident at right-angle to the fiber-axis in (a) and at an angle to the fiber-axis in (b).

Z H

S

F

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(b)

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(a) (b)

Multiscale Structures in Polymers and nanocomposites

Sanjeeva N. Murthy, University of Vermont & State Agricultural College, DMR 0513926

Educational Activities

A graduate student (Mr. Wenjie Wang) working on this project is about complete is Ph.D. dissertation. He visited the Argonne National Laboratory four times to collect the data and gain experience working at a national facility. He is also working on other projects related to copolymers, fibers, films and plastics so as to broaden his expertise. A post doctoral student (Dr. Fahmi Bedoui), has almost finished his tenure on this project. He has been able to publish 2 papers and 3 more are about to be submitted for publication. Over the past year, he spent time in training several undergraduates and graduate students in their research. The PI is now involved in training undergraduate and graduate students in physical property evaluation of biomaterials at the Rutgers University.

Outreach● PI hosted an undergraduate student from U.S.

Virgin Islands during the summer of 2007 as a part of a larger program at Rutgers University. This student was involved with surface modification of polymers using laser ablation.

● PI hosted a graduate student from Singapore, as part of the larger program within the New Jersey center for biomaterials. This student worked on the influence of hierarchical structures in copolymers on their elastomeric properties.

● PI has been working with a company, X-ray Optical Systems (Albany, NY), to transfer the know-how in x-ray analysis into a commercial product through an SBIR Phase I proposal.