Design And Preparation Of Carbon Nanotubes-based Nonlinear Optical Polymer Functional Materials

Optical limiting is an important application of nonlinear optics, useful for the protection of human eyes, optical elements, and optical sensors from intense laser pulses. An optical limiter is such a device that strongly attenuates high intensity light and potentially damaging light such as focused laser beams,whilst allowing for the high transmission of ambient light. CNTs-based functional materials exhibit a broadband optical limiting response covering the visible to infrared region. But for CNTs, the lack of solubility and their difficult manipulation in any solvent have, imposed great limitations on their use. Many efforts have currently been invested into design and prepare soluble CNTs functionalized with polymers, which improve solubility and allow for the fabrication of films, coatings, or suspensions required for the use of nanotubes in a real optical limiting application.In the first Chapter, the optical limiting properties of carbon nanotube suspensions, solubilized carbon nanotubes, small molecules doped carbon nanotubes and polymer/carbon nanotube composites have been reviewed. The optical limiting responses of carbon nanotube suspensions are shown to be dominated by nonlinear scattering as a result of thermally induced solvent-bubble formation and sublimation of the nanotubes, while the solubilized carbon nanotubes optically limit is more complex.In the second Chapter, a novel MWNTs covalently functionalized with conjugated polymer PCBF-NH2, was synthesized. In the N1s XPS spectrum of MWNT-PCBF, an appearance of new peak at 402 eV corresponding to N bound to the carbonyl C (i.e., NH-C=O), which provides essential and useful information for the covalent attachment of the polymer onto the surface of MWNTs. Unlike PCBF-NH2, which only displayed a weak optical limiting response at 532 nm, Z-scan for MWNT-PCBF exhibited a much broader reduction in transmission and a scattering accompanying on the focus of the lens at both 532 nm and 1064 nm, indicating a prominent broadband optical limiting response. The thermally induced nonlinear scattering is responsible for the optical limiting.In the third Chapter, a new poly(N-vinylcarbazole)-covalently grafted single-wall carbon nanotubes(SWNT-PVK) hybrid material was synthesized by an in situ anionic polymerization reaction of N-vinylcarbazole and the negatively charged SWNTs. Incorporation of the PVK moieties onto the SWNTs surface considerably improves the solubility and processability of SWNTs. At the same level of linear transmission, the SWNT-PVK dispersions show better optical limiting performance than the pristine SWNT dispersions, which manifest this material a suitable candidate for viable optical limiting devices. Micro-plasmas and/or micro-bubbles induced nonlinear scattering is considered as the main mechanism for optical limiting.In the forth Chapter, a new conjugated polymer PFC-CHO with pendent aldehyde groups in the polymer sidechains was synthesized by the Suzuki coupling reaction. Then, the polymer was successfully added to the MWNT surface via a simple 1,3-dipolar cycloaddition reaction to give a soluble MWNT-PFC hybrid material. In contrast to the Raman spectrum of MWNTs, the D-to G-band intensity ratio (ID/IG) for MWNT-PFC increased, which provides useful information for the attachment of the polymer onto the surface of MWNTs.In the last Chapter, we used polymer PVK to prepare PVK-NH2,which was reacted with MWNTs with surface-bonded acryl chloride moieties to give a soluble MWNT-PVK hybrid material. The stretching mode of an amido bond at 1706 cm(vNH-C=O) was detected in the IR spectrum of MWNT-PVK, which provides useful information for the attachment of the polymer onto the surface of MWNTs.