arXiv subjects

Leanne Friedrich

Publications and source records attributed to Leanne Friedrich.

3 recordsLinked to original sources

arXiv2021

Kaleidoscope Eyes: Microstructure and Optical Performance of Chiton Ocelli

The chiton Acanthopleura granulata uses aragonitic lenses embedded in its shell to focus light onto photoreceptors. Because aragonite is biaxially birefringent, the microstructure of the lens greatly impacts the optical performance. In addition, the chiton lives in the intertidal, so lenses experience two environments with different refractive indices: air and water. Using EBSD, we find that the lens is polycrystalline and contains curved grain boundaries. A combination of large, twinned grains and nanotwins ensure that the aragonitic <001> axis is consistent across the lens. However, the orientation of the <001> axis relative to the shell varies between lenses. Ray tracing simulations predict the optical performance of lenses of various microstructures in wet and dry environments. Though twinning helps to limit birefringence-induced aberrations, variations in the orientation of the <001> axis between lenses lead to variations in focal lengths between lenses and cause image doubling in some lenses. As such, the birefringence of aragonite does not help the lens to transmit focused images in both air and water.

physics.bio-ph↗

arXiv2020

Corner accuracy in direct ink writing with support material

3D printing methods which enable control over the position and orientation of embedded particles have promising applications in cell patterning and composite scaffolds. Extrusion-based additive manufacturing techniques such as fused deposition modeling and direct ink writing can experience particle patterning defects at corners which could hinder cell survival at corners and create unintended property gradients. Here, we propose models which predict the behavior of deposited lines at corners for moderate viscosity inks which are impacted by both capillarity and viscous dissipation. Using direct ink writing with acoustophoresis and a Carbopol-based support gel, we write polygons out of dental resin-based composite inks containing a narrow distribution of microparticles at the center of the filament. A Laplace pressure differential between the inner and outer surfaces of the corner drives corner smoothing, wherein the inner radius of the corner increases. Double deposition, or printing on the same area twice, drives corner swelling, wherein excess ink is diverted to the outer edge of the corner. Fast turns at corners produce ringing, wherein vibrations in the stage manifest in oscillations in the print path. Swelling and ringing effects are apparent in the particle distributions at corners immediately after deposition, while smoothing effects are apparent after the printed structure has had time to relax. When the nozzle returns to write a neighboring line, it imposes shear stresses which mitigate inconsistencies in microstructure at corners by erasing defects which appeared during relaxation. Using a support bath instead of layer-by-layer support suppresses microstructural corner defects.

physics.app-ph↗

arXiv2019

Flexible Conductive Composites with Programmed Electrical Anisotropy Using Acoustophoresis

3D printing mechanically flexible composite materials with high electrical conductivity is currently hindered by the need to use high loading of conductive filler, which severely limits flexibility. Here, microstructural patterning of composite materials via acoustophoresis imparts these materials with high conductivity and flexibility simultaneously, filling a technology gap in the field. Acoustophoresis patterns filler particles into highly efficient percolated networks which utilize up to 97\% of the particles in the composite, whereas the inefficient stochastic networks of conventional dispersed-fiber composites utilize $<5$\%. These patterned materials have conductivity an order of magnitude higher than conventional composites made with the same ink, reaching 48\% the conductivity of bulk silver within the assembled silver-particle networks (at 2.6v\% loading). They also have low particle loading so that they're flexible, withstanding $>$500 bending cycles without losses in conductivity and changing conductivity only $5$\% within cycles on average (for 2.6v\% composites). In contrast, conventional unpatterned composites with the same conductivity require such high loading that they're prohibitively brittle. Finally, modulating the shape of the applied acoustic fields allows control over the anisotropy of the conductive networks and produces materials which are either 2-D conductive, 1-D conductive, or insulating, all using the same nozzle and ink.

physics.app-ph↗