Browsing by Author "Rodriguez-Macias, Fernando J."

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    Fully integrated single-walled carbon nanotube thermoplastic composites
    (2004) Rodriguez-Macias, Fernando J.; Barrera, Enrique V.
    The development of composites of single-walled carbon nanotubes (SWNTs) with thermoplastics requires methods for good dispersion and achieving good interaction between SWNTs and the matrix. This thesis presents a new method to achieve good dispersion by a preliminary treatment called incipient wetting. The SWNTs dispersed in a solvent are mixed with polymer particles and deposited over them as the solvent is evaporated to give an initial dispersion. Factors that make this more effective are: good wetting of the polymer by the solvent, swelling of the polymer, high surface area of the polymer. Swelling enhances the initial dispersion with some initial mixing. A high surface area is achieved using polymer powder. High shear mixing alone does not achieve the same uniform and repeatable level of dispersion that the combination with incipient wetting allows. The incipient wetting method was studied and applied to different polymers. The possibility of recovering SWNTs from thermoplastics by dissolving or burning away the matrix is an extension of this study. A new comprehensive approach to control the interface of thermoplastics with SWNTs is studied. This is based on achieving direct chemical bonding between polymer molecules and functional groups on oxidized open ends, sidewalls, or both, in the SWNTs. Different concepts and approaches to these "fully integrated nanotube composites" are discussed. The concepts have been applied to epoxies elsewhere and are tested here with nylon-6,6 as a model system. Nylon was synthesized by interfacial polymerization in the presence of SWNTs resulting in excellent dispersion in the composite without further processing. The essential requirement for good dispersion is that the SWNTs are well dispersed in the solvent. Interfacial polymerization opens the way to many types of polymer-SWNT composites. Tests of full integration of SWNTs with open ended nanotubes showed promising results and hints of integration but were limited by dispersion in the solvent. Fluorinated SWNTs were dispersed effectively with dichlorobenzene, another solvent may be better. There is no conclusive evidence of integration with F-SWNTs but they may react with the polymer chain with thermal post-processing.
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    Large-scale production and purification of single-walled carbon nanotubes
    (1999) Rodriguez-Macias, Fernando J.; Smalley, Richard E.
    Single Walled Nanotubes were produced in large scale by Laser Vaporization with maximum yields of 50%. Optimization experiments give relative yields of (Nickel Cobalt (1:1 atomic % each)) = (Nickel Tungsten (1:1)) $>$ (Nickel Yttrium (1.6:0.4)/Cobalt Platinum (0.9:0.3)) $>$ (Nickel Platinum (0.9:0.3)/Cobalt Platinum (1:1)/Nickel Yttrium (4.2:1)/Nickel Molybdenum (1:1)) $\gg$ (Ruthenium (0.5)). For changes in atmosphere the yields are Argon (500 torr) = Carbon Monoxide (700 torr) = Argon (700 torr) $\gg$ Helium (500 torr). Differences in yields are discussed and compared to results from the electric arc technique. The setup has been successfully scaled-up and operates for more than 36 hours. The target preparation and SWNT material purification procedures have been optimized and scaled-up accordingly to obtain grams of 95% pure SWNT routinely. High quality material is now available, from a facility called "tubes@rice", for research purposes.
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    Oriented nanofibers embedded in a polymer matrix
    (2011-03-01) Barrera, Enrique V.; Rodriguez-Macias, Fernando J.; Lozano, Karen; Chibante, Luis Paulo Felipe; Stewart, David Harris; Rice University; United States Patent and Trademark Office
    A method of forming a composite of embedded nanofibers in a polymer matrix is disclosed. The method includes incorporating nanofibers in a plastic matrix forming agglomerates, and uniformly distributing the nanofibers by exposing the agglomerates to hydrodynamic stresses. The hydrodynamic said stresses force the agglomerates to break apart. In combination or additionally elongational flow is used to achieve small diameters and alignment. A nanofiber reinforced polymer composite system is disclosed. The system includes a plurality of nanofibers that are embedded in polymer matrices in micron size fibers. A method for producing nanotube continuous fibers is disclosed. Nanofibers are fibrils with diameters of 100 nm, multiwall nanotubes, single wall nanotubes and their various functionalized and derivatized forms. The method includes mixing a nanofiber in a polymer; and inducing an orientation of the nanofibers that enables the nanofibers to be used to enhance mechanical, thermal and electrical properties. Orientation is induced by high shear mixing and elongational flow, singly or in combination. The polymer may be removed from said nanofibers, leaving micron size fibers of aligned nanofibers.