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Title:Core-shell printing of functional polymer filaments
Author(s):Lorang, David
Advisor(s):Lewis, Jennifer A.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Direct Writing
Additive Manufacturing
Polymer Filaments
Optical Waveguides
Carbon Capture and Storage
Abstract:Direct-write assembly is a filamentary fabrication technique capable of producing functional microstructures with a variety of materials, sizes, and morphologies. In essence, ink materials are extruded continuously from a printhead while the printhead is translated on a 3D positioning stage at a constant rate of travel. In the present work, core-shell printing techniques are introduced to expand the capabilities of direct-write assembly. Through the use of a viscoelastic shell ink, it is possible to print continuous filaments of a Newtonian liquid core without leakage or droplet breakup. This technique is applied to enable the printing of optical waveguides of the commercial photopolymer OrmoClear using a sacrificial shell of an aqueous solution of the block copolymer Pluronic F-127. The waveguides are cured through ultraviolet exposure to a solid state, then the shell is removed by washing with water, yielding OrmoClear-core, air-cladding waveguides that transmit light with loss of ~0.1 dB cm-1 and can be printed in complex 2D and self-supporting 3D networks. We investigated the flow of core-shell ink systems in straight channels and observed that an annular plug of unyielded viscoelastic shell ink provides a solid-like structure to resist droplet breakup of the inner (core) fluid. By incorporating a tapered tip into core-shell printheads, the size of printed core-shell features can be reduced. Unique to these printheads, the core and shell inks co-flow in contact before exiting the printhead. While flowing through the printhead, the shell ink undergoes shear thinning when its yield stress is exceeded, therefore the ink system must be suitably designed to prevent droplet breakup. Using tapered printheads, OrmoClear waveguides as small as 55 µm were printed through a 120 µm nozzle. By adjusting the relative flow rates of the core and shell inks, the diameter of printed waveguides can be adjusted within the range of 15–77 µm without any change in the printhead dimensions. Using curable polydimethyl siloxane (PDMS) shells, hollow and liquid-filled filaments are printed. The PDMS shell provides viscoelastic support during printing, however upon curing it becomes a permanent structure rather than a sacrificial support. Liquid-filled PDMS filaments containing a 30 wt% solution of sodium carbonate are synthesized, for CO2 capture and storage applications. The encapsulated liquid sorbent is observed to form sodium bicarbonate crystals as the CO2 concentration increases, and can be regenerated by heating, releasing the CO2 for storage. The PDMS filaments are stable, robust, and suitable for use as monolithic, patterned CO2 absorber elements.
Issue Date:2014-01-16
Rights Information:Copyright 2013 David Lorang
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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