טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentIrena Levin
SubjectOptical Properties of Thin Polymer Films Containing
Aligned Nanofiber Composites with Carbon Nanotubes
DepartmentDepartment of Polymer Engineering
Supervisors Full Professor Cohen Yachin
Full Professor Zussman Eyal
Full Thesis textFull thesis text - English Version


Abstract

Among their outstanding characteristics, carbon nanotubes (CNTs) have attractive nonlinear optical properties, making them a good candidate for the construction of passive optical power limiters (OPLs). OPLs are devices that exhibit a drop in transmittance as the energy of incident laser pulses increases, usually above a certain threshold and have the potential for protecting optical sensors and human eyes from laser pulse damage. In addition, due to their large aspect ratio and one-dimensional topology, CNTs possess anisotropic absorption. Therefore, aligned anisotropic CNTs in a solution or film can be used as light polarizer. This research is aimed to develop a transparent optical coating consisting of aligned composite nanofibers (NFs), with embedded aligned multi-walled carbon nanotubes (MWNTs), and possessing optical power limiting and polarization properties. For this purpose, the electrospinnig (ES) technique was used to fabricate a thin layer of composite NFs from a homogenous polymer solution (poly(acrylonitrile)- PAN or poly(methylmethacrylate)- PMMA) with dispersed MWNTs. The electrospun NFs were deposited in an aligned manner on a glass surface attached to the rotating wheel collector with the MWNTs aligned along the fiber axis due to the sink-like and elongation flows in the ES process. A combined polarizer and OPL device was constructed using an optically compatible polymeric resin and the optical performance of the device was evaluated. A high degree of NFs alignment was achieved in both systems using a rotating wheel as the collector in the ES process. Optical devices with good limiting performances were constructed from the composite. However, the poor alignment of the MWNTs within the NFs resulted in low degree of polarization. Although general alignment of the MWNTs in the NFs was observed in electron microscopy images, some segments of the MWNTs were twisted or even emerging out of the NFs. The reduced NFs diameter, which was achieved by introducing the PAN matrix instead of PMMA, and the improved NFs alignment, were not as significant as the quality of the MWNTs, which was found to be the main obstacle in the fabrication of composite material with aligned MWNTs.

A triblock copolymer of PMMA-b-polystyrene-b-PMMA (MSM) was used as a dispersant in PMMA based system. Since the quality of the electrospun dispersion is of great importance, the structure of the MWNTs/copolymer hybrid was investigated by small angle neutron scattering using contrast variation technique. The calculated values from the suggested model were in agreement with the values estimated from cryoTEM images.