A nanolaminate manufacturing technique for multifunctional materials and devices
A new method of quickly, simply, and efficiently assembling nanolayered materials and devices is developed. The method is called Spin-Spray Layer by Layer Self Assembly (SSLbL) and is a modification of the well-established Layer by Layer Self Assembly (LbL) method. SSLBL is a conceptually simple process. Very dilute, aqueous solutions of polymers, nanoparticles, or other colloids are sprayed onto a rapidly spinning substrate, quickly spreading over the surface. As the solvent evaporates, the chosen polymer or colloid adheres to the surface via electrostatic, physical, and other interactions. Typically this process is carried out in bilayers of colloids or polymers that are attracted to each other. Called nanolaminae, these bilayers are the fundamental building blocks of SSLbL. With thicknesses on the order of a single nanometer, nanolaminae consisting of different materials can be stacked in almost any sequence, allowing the creation of nanostructured materials.^ A model of the SSLbL process is developed based primarily on spin-coating physics. This model gives a qualitative understanding of the dynamic fluid processes as well as quantitative results. These quantitative results include the amount of solution that should be sprayed on a spinning disk, the solution concentration, and dry time. The parameters gained from the model are used as inputs for SSLbL experimentation.^ SSLbL experimentation is then shown to both validate the model as well as offer fine-tuning of the parameters for specific materials or applications. SSLbL represents a significant advancement of the state of the art by increasing the speed and efficiency of existing LbL techniques. It is demonstrated here to be capable of effectively building high quality nanolaminae similar to those produced via LbL. However, SSLbL is significantly faster, constructing each nanolamina in about 20 s, compared to 20min using LbL, an improvement of two orders of magnitude. Additionally, traditional LbL is quite wasteful, with less than 1% of the initial polymers or colloids being incorporated into the original film. In contrast, SSLbL is shown to have material usage efficiencies of over 50%, and this can be further improved. Three dimensional SSLbL structures are also demonstrated using shadow masks. This represents a very unique development by allowing any LbL-type material to be built with in-plane structure without the use of a removal step or the limitations of being able to use only a few specific materials with unique properties.^ Finally, a few sample applications utilizing SSLbL are demonstrated. These include a battery electrode and a strain gage. In neither case was a significant technological breakthrough achieved. However, both studies resulted in the further development and improvement of the SSLbL system and of fundamental work in electrically conductive nanolaminates. More importantly, these applications demonstrated the power of SSLbL to build a wide variety of different materials. This ability, combined with the speed, efficiency, and flexibility of the method give indication of the potential of this new method in both research and potential manufacturing environments.^
C. T. Sun, Purdue University.
Engineering, Materials Science
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