טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLiberman Solomon Lucy
SubjectNanostructural Phase Behavior Study of Carbon Nanotubes in
Superacid Solutions
DepartmentDepartment of Chemical Engineering
Supervisor Professor Emeritus Yeshayahu Talmon
Full Thesis textFull thesis text - English Version


Abstract

Carbon nanotubes )CNTs), on their molecular level, are characterized by a special combination of mechanical strength, electrical and thermal conductivity, and low mass density. These excellent properties turn CNTs into leading candidates for development of wide variety of CNT-based applications. The best way to translate the superior single molecule properties into macroscopic material, is through liquid-phase processing.

The integration of CNTs in applications was significantly promoted with the discovery of spontaneous molecular dissolution of CNTs in chlorosulfonic acid (CSA), which results in a thermodynamically stable solution. The phase behavior of the CNT/CSA system exhibits different stages as a function of CNTs concentration. At low concentrations, the CNTs are individually dispersed in an isotropic phase, while higher CNT content leads to the formation of an ordered nematic liquid crystalline phase. The properties of the CNT-based macroscopic structures are dictated by the properties and the degree of alignment of the CNTs.

 In our research we used a variety of advanced electron microscopy techniques, especially, cryogenic-electron microscopy (cryo-EM), while combining these with complementary indirect techniques, such as Raman spectroscopy and small-angle neutron scattering (SANS) for the nanostructural and chemical characterization of CNT/CSA, and other liquid systems. We explored the effect of varying system parameters for the basic understanding of the phase behavior of the CNT/CSA solutions, which is crucial for the optimization of liquid phase processing, towards a multifunctional CNT-based applications.

By applying unique cryo-EM specimen preparation and imaging methodologies suitable for strong acids, developed in our lab, we were able to follow the nanometric evolution of the CNT/CSA phases as a function of their aspect ratio, diameter, number of walls, and purity. Based on our research, we observe that most of the CNT/CSA systems follow the phase behavior of rigid rod polymers. However, we discovered a new phase behavior regime for small diameter, high aspect ratio CNTs, which results from their higher flexibility, and more degrees of freedom. Moreover, with SANS we were able to study quantitatively the bulk solution properties of CNT/CSA solutions as a function of concentration and aspect ratio.

To improve our cryo-SEM imaging methodology, we have studied the micrograph contrast mechanism at low-voltage SEM and cryo-SEM of different systems. Optimization of the SEM parameters improves the micrograph contrast, which is essential for the study of different-scale features in ceramics, polymers, organic materials, and liquids, and, especially, in biological research. We examined the effect of the acceleration voltage and detector type on the contrast of materials with different electrical conductivity and atomic number, with emphasis on materials rich in carbon and oxygen, e.g., water, oils, and CNTs.

We took advantage of our cryo-TEM skills and the state of the art new FEI Talos 200C, and studied the insertion of alpha-hemolysin (αHL) into lipid membranes to form active, and functional pores. We directly imaged native αHL induced pores in lipid bilayers for the first time. αHL protein is subject of fundamental biological research and is being applied in advanced biotechnological developments.