|M.Sc Student||Katz Liran|
|Subject||Compounding and Orientating Nanofibers for the Formation of|
Transparent Optical Coatings
|Department||Department of Chemical Engineering||Supervisors||Professor Yachin Cohen|
|Professor Eyal Zussman|
|Full Thesis text|
Optical power limiting (OPL) components made of artificial nanostructured materials are highly desirable for the protection of various optical instruments, from fiber-optic telecommunication systems to everyday life purposes, such as sunglasses and windows. Their ability to control and regulate high intensities of light using only nonlinear light-matter interactions, make them simple and low-cost substitutes compared to conventional external (e.g., mechanical or electrical) options. An OPL device can limit high intensities of light while allowing high transmittance of low intensity ambient light. Different organic materials (e.g., carbon nanotubes - CNTs, fullerenes, porphyrins, carbon black, etc.) exhibiting nonlinear optical properties, can be embedded into a dielectric host to create OPL solutions and components. Due to their tubular structures made of graphite layers and their strong light absorption, aligned anisotropic CNTs in a solution or film can be used as a polarizer in addition to their limiting abilities.
In our work, we used a simple process named Electrospinning (ES) to fabricate composite nanofibers (NFs) of poly(methyl methacrylate) - PMMA with embedded CNTs from a common solution. The solution was successfully made as a homogenous CNT/PMMA dispersion by a unique nondestructive technique to ultimately yield a uniform film for the creation of the OPL device. The use of triblock copolymer - poly(methyl methacrylate)230,000-(styrene)162,000-(methyl methacrylate)230,000 and sonication methods significantly reduced the CNTs agglomerates and stabilized the solution for a period of several weeks. Using an alignment method, we created a semi-transparent OPL film (~50% transmittance) comprised of oriented nanofibers (standard deviation of 14º from the main director of the film) with different CNT compositions and film thicknesses. The nanofibers' alignment using the electrospinning process could create an alignment of the CNTs, so additional optical abilities (such as, polarization) can be reached. The optical devices showed spectral response at normal intensities of light throughout the visible light region. Furthermore, high limiting abilities (compared to works with similar compositions and purposes) were achieved with a limiting threshold of 1.5J/cm3 at about 50% linear transmittance. Light polarization was observed with some degree of polarization.