This grant provides funding for research into a method for fabricating a new class of three-dimensional polymer matrix nanocomposites with custom designed functionally graded properties. The objective of the research is to synthesize structural composites designed with specific regions that have different stiffness, strength, and toughness values that optimize the overall mechanical and thermal performance of the composite. The materials of interest are formed from chemically reactive liquid crystal monomers containing carbon nanotubes. Liquid crystal monomers are unique in that they can be selectively oriented by magnetic or electric fields and can then be locked in place by photoreaction of the monomers in-situ. It is anticipated that orienting the liquid crystal molecules which contain nanotubes will cause self-alignment of the nanotubes, resulting in composites that have enhanced anisotropic mechanical properties. The nanocomposites can be formed by an inkjet deposition process and it is anticipated that local variations in alignment as well as composition can be accommodated by changing the direction of the applied field during processing. Modeling the material and process will enable the custom design of three dimensional nanocomposites with superior performance for advanced applications.
Using this process, it is possible to form nanotube-polymer composites that are stiffer, tougher, and at the same time lighter weight than the best available carbon fiber-epoxy composites. Fully computerized solid freeform fabrication processing via inkjet deposition could enable the direct production of nano-composites and eliminate the use of conventional casting, forging, machining, or molding processes and the use of expensive tooling. This process is fast and accurate and is potentially capable of forming large sized composite structures. The ability to produce custom shapes at will lends itself to rapid, flexible, customized production at any location such as on ships at sea for production of one-of-a-kind critical composite components.
The University of Oregon conducted a research program on a novel method for fabricating 3-dimensional ultra-strong nano-composites from molecules that can be aligned with a magnetic field. The materials of interest are formed from special molecules called liquid crystal monomers (LC) and contain carbon nanotubes (CNTs). These LC monomers are selectively oriented by magnetic or electric fields and the orientation is then locked in by photoreaction using UV light to convert the liquid into a polymer. The nano-composites are formed via an inkjet printing process (IJP) so that local variations in alignment as well as composition can be accommodated. The objective of the research was to synthesize structural composites designed with specific regions that have different stiffness and strength values defined so as to enhance their overall mechanical performance. One might refer to such composites with strategically designed, properties as "3D-designer composites". The inkjet deposition process (IJD) for fabricating these materials is a variation of the popularized computer controlled 3-D printing, which is a layered, additive-manufacturing approach. IJD is advantageous because it allows great flexibility for the introduction of local changes in material composition (or gradients) within the structure by incorporating various compositions during formation of the composite. Thus, composites formed by this method can be custom designed for superior performance in advanced applications, with the design directly integrated with the composite synthesis. The IJD process is fast and accurate. It also lends itself to forming large sized composite structures using current generation large-bed, high speed inkjet printers. This type of computer-controlled process allows for the direct production of high-performance composites without the use of conventional casting, forging, machining, or molding. It also does not require intermediate production steps or manual intervention. This offers possibilities for production cost savings in both time and labor as well as the ability to produce customized composite parts at sites where the parts are actually used. The ability to produce new shapes at will lends itself to rapid, flexible, customized production in various venues. The most important structural property for a polymer composite is its stiffness. We have shown that using the molecular alignment approach we have been able to produce composites that were up to 250% stiffer than the polymer using less than 1% of carbon nanotubes. The stiffness could be varied by changing the molecular orientation and concentration of the nanotubes. The stiffness values obtained were comparable to those for commercial carbon fiber-epoxy composites containing 35% of carbon fibers, while the LC nano-composites were half the weight. Practical aspects of constructing 3-D composites by inkjet printing include producing distinct and precise object borders and seamless interfaces between the printed layers. Techniques for achieving these were implemented. Software for converting design data into instructions for IJP composite part building also was developed. Research work on the program resulted in furthering the education of 2 post-doctoral researchers and 3 graduate students. There were 3 journal publications. The results provided case studies that have been incorporated into a graduate course at the University of Oregon. Composite design data were generated by work done by colleagues at Michigan Technological University who were partners on this project.
