Biphasic Nanoparticle Inks for Direct Write Assembly of Three-Dimensional Periodic Structures
Rao, Ranjeet Balakrishna
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https://hdl.handle.net/2142/82833
Description
Title
Biphasic Nanoparticle Inks for Direct Write Assembly of Three-Dimensional Periodic Structures
Author(s)
Rao, Ranjeet Balakrishna
Issue Date
2008
Doctoral Committee Chair(s)
Jennifer Lewis
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
Novel nanoparticle inks have been created for the direct-write assembly of 3-D periodic structures with fine scale (∼ 10 mum) features. These nanoparticle inks are composed of two populations of nanoparticles defined by the type of dispersant used to stabilize them, either poly(acrylic acid)(PAA) or a comb polymer comprised of a PAA backbone and poly(ethylene oxide)(PEO) teeth (PAA/PEO). The PAA/PEO-coated nanoparticles remain stable, and hence behave as repulsive species in suspension under high ionic strength conditions or in the presence of oppositely charged polyelectrolytes. By contrast, PAA-coated nanoparticles aggregate under these same conditions, and hence behave as attractive particles. Mixtures of these two nanoparticle populations allow one to broadly tune the elastic properties of the resulting suspension either by varying their total volume fraction or ratio of attractive-to-repulsive species. The rheological properties of these biphasic mixtures were measured through shear viscometry, oscillatory shear rheology, and compressive rheology. Biphasic mixtures have shear elastic properties intermediary between repulsive glasses and attractive gels, yet the scaling of their elastic properties with respect to volume fraction is dominated by the gel phase. By contrast, their compressive yield stress exhibits a volume fraction dependence that varies systematically between that observed for glasses and pure gels. More importantly, the compressive-to-shear yield stress ratio exhibits a pronounced volume fraction dependence, such that biphasic mixtures of intermediate composition exhibit a greater resistance to pressure filtration (or jamming) during direct ink writing. Using these novel inks, 3-D periodic structures are patterned with features approaching 10 mum, which correspond to nearly an order of magnitude reduction in size compared to those produced from pure gel-based inks.
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