Zhiyong Liang

This invention offers a novel technique to fabricate large-scale, lightweight electrically conductive cable using carbon nanotubes (CNTs). CNTs have good intrinsic electrical conductivity. However, entangled structures of CNTs in the form of yam or sheet has lower conductivity due to intertube contact resistance and gaps in between. Lightweight and high electrically conductive CNT materials can be used for cables for such applications as signal or power transmission, electromagnetic interference (EMI) shielding in electronic devices and lightning protection in aircraft etc.

An integrated approach of three major steps was used to improve the CNT sheet conductivity:

1) Mechanical stretching of entangled CNT sheets provides CNT alignment. Random and pristine CNT sheets in rolls were continuously stretched producing narrow and densely packed CNT networks, which reduced intertube contact resistance. With increased alignment, conductivity improved two or three times higher compared to the pristine, randomly aligned CNT sheets. This process can be performed continuously and scale-up production is possible.

2) A doping approach increases the carrier concentration of CNTs. For this purpose, vapor phase iodine doping was adopted, which can be expanded to other oxidizing liquids (acids such as HNO3, HCI or SOCh). Upon this chemical doping process, conductivity improved 3-4 times and a final room temperature conductivity of 10,000 Siem (up to 13,000 Siem). The doping process is a typical diffusion process and conductivity saturated after several hours, and its speed is depended on the packing of CNTs and mobility of the dopant and followed by time.

3) An approach to coating dramatically increased the cable stability. After doping process, the dopants are diffused out and kept inside the CNT yams/sheets to maintain the conductivity. For this purpose, doped CNT sheets were dipped in air stable conducting polymer, poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)(PEDOT:PSS). The thin polymer coating on the surface provides synergetic effects for the conductivity and a protection layer. Different polymer layers, such as polyvinyl ch loride, polyethylene and rubber can also be used as protection layers as for conventional cables.

This invention provides a novel technique to make high-performance carbon nanotube (CNT) polymer composite through integrating alignment and tailored degree of functionalization of carbon nanotubes. Lack of alignment, weak interface bonding, and low CNT concentration are major obstacles for developing high mechanical performance CNT reinforced composites. The team at FSU has developed several unique techniques to realize alignment and interfacial bonding improvement through chemical functionalization. With the demonstrated alignment and tailored functionalization, record-high mechanical performance of CNT polymeric matric composites can be achieved. Active epoxide groups on CNTs created through the chemical functionalization can react with amine and phenolic hydroxyl groups. Therefore, interfacial bonding between nanotube and matrices, such as epoxy and bismaleimide (BMI) resin, can improve resulting nanocomposites. Specifically, the proper combination of alignment enhancement and tailored functionalization led to record high mechanical and electrical performance. This novel method created high mechanical properties exceeding state-of-the-art carbon fiber composites which are widely sued in aerospace, defense, and sporting goods, etc.

An innovative method to detect fiber preform problems and design optimum resin flow strategy in vacuum assisted resin transfer molding (VARTM) process, a common manufacturing process in composite industry has been created. In this new method, prior to part production, a removable test liquid, such as alcohol, is infused into the production mold with fiber preform laid up inside. The flow pattern of the test liquid is recorded for flow analysis purpose. The test liquid is then removed by vacuum and temperature. As the test liquid flow behavior is similar to that of resin, the acquired test liquid flow pattern information can be used to direct and optimize process design/control of resin flow to eliminate flow-induced defects. For instance, the test liquid flow pattern can be used to detect the locations where defects might occur and the corresponding control action can then be determined for production (resin flow).

An advantage of this method is that it does not need any sensors, but instead, uses the low cost test liquid (such as alcohol) to pre-infuse the fiber preform prior to the resin infusion to detect any fiber perform problems and to predict resin flow pattern, through which the optimum resin flow process design can be obtained. The method provides effective and practical technical solutions to facilitate process design and control of VARTM process for defect-free part fabrication. This new method can significantly reduce the manufacturing cost by improving first-time success rate (reducing the defects related wastes/cost). This technique is particularly useful for large and complex part fabrication where flow-induced defects are common in manufacturing.

The present invention describes a method of creating lightweight efficient parabolic solar panels and a unique approach to realize improved alignment of nanotubes in buckypaper materials.

This invention provides a new method to align carbon nanotubes in buckypapers by stretching thermoplastics/buckypaper films. Buckypaper is a thin film (approximately 20µm) of nanotube networks, which can be utilized in various products, such as composites, electronic devices and sensors. Since nanotubes are highly anisotropic in nature, the alignment of nanotubes in buckypaper is critical for achieving high mechanical performance and high electrical and thermal conductivity.

Applications:

• This invention has an excellent potential for use in the mass production of high-performance nanotube and nanofiber-reinforced epoxy composites
• The significantly improved alignment is key factor toward realizing the potential of nanotubes for high mechanical, electrical and thermally conductive applications in composites and electronic devices
• The high-performance buckypaper nanocomposites can be used for EMI shielding, thermal management and structural materials applications
• Immediate applications include composite applications for aircraft and thermal management for electronic device package. High-performance buckypaper materials are also expected to be widely used to develop lightweight-conducting films and current-carrying materials for electronic products

FSU researchers created a lightweight and flexible heat sink based on carbon nanotube (CNT) sheet which can also be expanded to other lightweight sheets such as graphene and boron nitride free-standing sheets. CNTs have good electrical and thermal conductivity with large surface to volume ratio due to its nanostructures and these properties are good for heat dissipation. Compared to the conventional aluminum heat sink or copper heat pipes, CNT sheets are more lightweight and have more flexibility; this reduces the manufacturing cost and makes it possible for versatile application with easier shape deformations.

Different CNTs can be used for free-standing sheet fabrication either multi-walled CNT and/or double-walled CNT. Entangled CNT structures show voids and large surface area and this also increase the convective heat dissipation in addition to the thermal conduction. Also the novel heat sink design has increased surface area to enhance the convective heat dissipation and flexible CNT sheet can increase the design freedom of the heat sink with higher number of fins for larger surface area for convection. Furthermore, the overall thermal conductivity is low.

FSU researchers created a novel technique to improve the lightweight electromagnetic interference (EMI) shielding properties based on preformed thin films or buckypaper layers made of single-walled carbon nanotube (SWNT), multi-walled carbon nanotube (MWNT), carbon nanofibers (CNF), and their mixed forms in composites.  Carbon nanotubes are promising material for EMI shielding because of their electrical conducting properties and lighter weight compared to metal. Film materials made of entangled network using carbon nanotubes, called buckypapers (BP), provides free standing films. The film materials are easy to be use and integrate into various structures and composites fabrication processes to reduce manufacturing cost. Nanotube buckypapers can have an areal density from 18.1 g/m² to 21.5 g/m², while offering electrical conductivity as high as 50S/cm to 8,000S/cm.

To improve the EMI shielding effectiveness (SE), layers of BP were stacked together. The absorption loss increased due to the increased thickness of conducting material since the thickness of individual BP layers is usually less than 30 mm. However, in experiments, the EMI SE does not linearly increase with the increased of number of BP layers directly stacked together. Since the absorption contribution to the total SE is small as a result of directly stacking multiple BP layers together, we discovered a new method to effectively utilize internal multiple reflection effects to further improve the SE. This invention achieves high EMI shielding effectiveness by inserting polymer insulators in between conducting nanotube buckypaper layers in composites.

The present invention describes a carbon-materials-based membrane electrode assembly (MEA) for a fuel cell comprising a catalyst layer.

The catalyst layer can include a plurality of catalyst nanoparticles, e.g., platinum, disposed on buckypaper. A particular feature of the MEA, according to the invention, is that the buckypaper film is fabricated with carbon nanotubes, nanofibers, or a mixture thereof, with little or no binder. The buckypaper additionally can be treated with high temperature for improving electrical and/or mechanical properties of the structure. The microstructure of the buckypaper can be tailored by adjusting the starting materials and nanotubes dispersion so as to achieve a desired porosity, pore size, surface area, and electrical conductivity for use as the catalyst layer of the MEA. The catalyst nanoparticles are preferably deposited directly at the most efficient sites of the buckypaper to thereby maximize the three-phase reaction coefficient.

The MEA so fabricated can have a higher catalyst utilization rate at the electrodes, can provide higher power output, and can have enhanced oxidation resistance, and well as a longer service life, as compared to conventionally-fabricated fuel cells.

Carbon nanotubes are ideal for polymer matrix composites due to their mechanical and electrical properties. However, to date, the overall properties of CNT-polymer composites have not reached their full potential due to poor dispersion and low concentrations of CNTs. Our new scalable process yields high-CNT content (60 wt%) polymer composites using a simple, three-step process:

1. A filament winding process that allows for control of CNT orientation and overall composite thickness.
2. A mechanical stretching process that has shown improved CNT alignment and overall composite properties.
3. A curing process under tension that further stretches and aligns the CNTs in the stress direction.

These improved polymer composites are ideal for defense applications and deep space exploration.

This invention provides a novel technique to enhance carbon nanotube dispersion and interfacial bonding in epoxy-based nanotube nanocomposites through in-situ polymerization. The in-situ polymerization reaction grafts peroxide groups onto the surfaces of nanotubes and the functionalized carbon nanotubes or nanofibers react with epoxy resin during nanocomposites fabrication. This in-situ polymerization can lead to high-exfoliation and uniform dispersion of carbon nanotubes or nanofibers in the epoxy polymer matrix during modification of nanotube surface characters. Furthermore the in-situ reaction produces covalent bond between nanotubes or nanofibers and the epoxy polymer matrix during composite fabrication through drafted peroxide groups to substantially improve load-transfer between nanotubes and resin. The significantly improved dispersion and interface bonding considerably increase the load-transfer and acquire high performance.

Applications:

• This invention has excellent potential for use in the mass production of high-performance nanotube and nanofiber reinforced epoxy composites for multifunctional applications, such as lightweight high-performance structural materials, electromagnetic interference, and thermal management materials, etc.
• Immediate applications include composite applications for aircraft, thermal management for electronic device package, etc. The yield rate using this method is almost I 00% and has the excellent potential for low cost mass production and scale-up.

This present invention describes a novel technique to fabricate carbon nanotube or nanofiber thin films (buckypapers)/solid electrolyte actuator devices for lightweight, high performance actuator and morphing structure applications. The method includes two nanoscale fiber films adjacent to a solid polymer electrolyte positioned at least partially in between. Moreover, the solid polymer electrolyte is affixed to the two nanoscale fiber films. The nanoscale fiber films may be buckypapers made of carbon nanotubes. The actuator is capable of dry actuation.

This new approach to prepare buckypaper actuators can eliminate the need to use insulation layer in structures and retains high concentration and conducting of nanotube networks in the actuators, which are critical to achieve high performance actuation. More importantly, all the actuators can work properly in open air, which is critical for real-world applications. High nanotube loading and good conducting networks in buckypapers lead to improved actuation performance. Furthermore, the actuator can be easily laminated or encapsulated with polymer films or coating to resist environmental effects. Through improvements of nanotube dispersion, alignment and conductivity of buckypapers, we can further enhance and optimize actuation performance. The invention is a technical breakthrough to realize real-world engineering applications of nanotube-based actuators. The invention overcomes the major technique barriers, such as working in liquid electrolyte and lower performance, of current liquid electrolyte and nanotube/polymer mixture-based actuator systems.

Due to exceptional high mechanical properties and lightweight of carbon nanotube and nanofiber materials, lightweight and high performance actuation can be expected for both immediate and near future engineering applications, such as morphing structures of aircraft and nanoscale/microscope actuators for device applications (for instance, actuators for driving microscale).