Graduate Thesis Or Dissertation
 

Leveraging Fluids with Weak Yield Stress for Directed Alignment and Distribution of Magnetic Disks in Novel Inks

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1n79h9186

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  • Additive manufacturing and 3D printing have become household names as both hobbyistsand industrial manufacturers utilize fast, inexpensive prototyping and production of functionalparts. Additive manufacturing is being revolutionized with 3D printers such as theMulti Jet Fusion 3D from HP, Inc., where each volume pixel, or voxel, can be independentlyfunctionalized. Voxel-by-voxel printing allows each voxel to be printed with characteristicsthat are independent from its neighbor, producing gradients in color, elasticity, surfaceproperties, strength, and higher-order functionality. Voxel-level functionality enables forproduction of high-value-added, highly customizable parts. The potential for higher-orderfunctionality (e.g., anisotropic material properties) revolutionizes 3D printed parts from beingconfined by material properties to being driven by the ability to vary material propertieswithin the printed part. Novel inks are currently being developed that provide functionalitywith the addition of inclusions, such as magnetic disks.Two common problems that are experienced while functionalizing inks with magneticdisk inclusions are sedimentation and chaining. Studying the timescales that are associatedwith particle sedimentation, orientation, and translation during the printing processpresents the need for development of a fluid that prevents sedimentation and translationwhile allowing for particle orientation. Characteristic flow behavior of non-Newtonian fluidsexhibit a range of performance regimes with their ability to suspend particles at rest whilealso allowing for inkjet ejection. Fluids that exhibit a yield stress, the specific stress thatmust be applied to achieve flow, have been shown to assist in preventing particle sedimentation.Weak yield stress fluids (xanthan gum T622 and gellan gum CG-HA, CP Kelco)were characterized using rotational rheometry to correlate bulk rheological behavior withphenomena that is exhibited in particle-orientation and particle-sedimentation experiments.A protocol to easily identify yield stress in a low-viscosity, high-molecular-weight fluid wasdeveloped. Effects of polymer concentration on the yield stress was examined. Standardrheological characterization under steady shear and small-amplitude-oscillatory shear is alsoreported. Finally, this work provides a proof-of-concept for utilizing a fluid with a weak yieldstress that prevents sedimentation and translation during directed alignment of magneticparticles in a rotating magnetic field. Magnetic particles with a random orientation distributionwere successfully aligned and uniformly oriented, without translation, to maintaincenter-of-mass particle distribution within the fluid.
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