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Research Papers

Additive Manufacturing With Conductive, Viscoelastic Polymer Composites: Direct-Ink-Writing of Electrolytic and Anodic Poly(Ethylene Oxide) Composites

[+] Author and Article Information
Sepehr Nesaei

School of Mechanical and Materials Engineering,
Washington State University,
405 NE Spokane Street,
Pullman, WA 99164
e-mail: sepehr.nesaei@wsu.edu

Mitch Rock

School of Mechanical and Materials Engineering,
Washington State University,
405 NE Spokane Street,
Pullman, WA 99164
e-mail: darman.rock@wsu.edu

Yu Wang

School of Mechanical and Materials Engineering,
Washington State University,
405 NE Spokane Street,
Pullman, WA 99164
e-mail: yu.wang3@wsu.edu

Michael R. Kessler

School of Mechanical and Materials Engineering,
Washington State University,
405 NE Spokane Street,
Pullman, WA 99164
e-mail: michaelr.kessler@wsu.edu

Arda Gozen

School of Mechanical and Materials Engineering,
Washington State University,
405 NE Spokane Street,
Pullman, WA 99164
e-mail: arda.gozen@wsu.edu

1Corresponding author.

Manuscript received March 13, 2017; final manuscript received June 18, 2017; published online September 13, 2017. Assoc. Editor: Zhijian J. Pei.

J. Manuf. Sci. Eng 139(11), 111004 (Sep 13, 2017) (12 pages) Paper No: MANU-17-1146; doi: 10.1115/1.4037238 History: Received March 13, 2017; Revised June 18, 2017

Conductive viscoelastic polymer composites (CVPCs) consisting of conductive fillers in viscoelastic polymer matrices find numerous applications in emerging technologies such as flexible electronics, energy storage, and biochemical sensing. Additive manufacturing methods at micro- and mesoscales provide exciting opportunities toward realizing the unique capabilities of such material systems. In this paper, we study the direct-ink-writing (DIW) process of CVPCs consisting of electrically conductive additives in a poly(ethylene oxide) (PEO) matrix. We particularly focus on the deposition mechanisms of the DIW process and the influence of these mechanisms on the printed structure geometry, morphology, and functional properties. To this end, we utilized a novel practical approach of modeling the ink extrusion through the nozzles considering the non-Newtonian viscous effects while capturing the viscoelastic extensional flow (drawing) effects through the variation of the nozzle exit pressure. We concluded that inks containing higher amounts of high molecular weight (HMW) PEO exhibit drawing type deposition at high printing speeds and low inlet pressures enabling thinner, higher aspect ratio structures with ideal three-dimensional stacking. Under this deposition mechanism, the electrical conductivity of the anodic structures decreased with increasing printing speed, indicating the effect of the drawing mechanism on the printed structure morphology.

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Figures

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Fig. 1

DIW process and system details: (a) two different regimes of DIW, (b) the DIW system used in this study, and (c) schematic description of the ink flow path during the DIW

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Fig. 2

Results of the DIW experiments with electrolytic inks regarding the exit pressure variation and its impact on printing: (a) lines printed using EL0 at 5 psi inlet pressure and 180 mm/s printing speed, (b) lines printed using EL3 at 5 psi inlet pressure and 180 mm/s printing speed, (c) shear rheology of the electrolytic inks, (d) shear rate of the electrolytic inks during DIW as a function of printing speed, (e) Pd values calculated for the electrolytic inks as a function of the printing speed, (f) Pd values calculated for the electrolytic inks as a function of the inlet pressure, and (g) schematic description of the two different deposition mechanisms experienced by different electrolytic inks

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Fig. 3

Results of the DIW experiments with electrolytic inks regarding the printed structure geometry: (a) normal force measured during the flow ramp test of the electrolytic inks indicating the expansion of EL1, 2, and 3 with increasing shear rate, (b) microscopy image of the EL3 ink flowing out of the nozzle indicating the die-swell behavior, (c) width and (d) height of the electrolytic lines as a function of printing speed, (e) cross-sectional profiles of the printed multilayer electrolytic lines, and (f) results of the amplitude sweep of the electrolytic inks

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Fig. 4

Results of the rheological characterization and DIW experiments with anodic inks regarding the exit pressure: (a) shear rheology of the anodic inks obtained through the flow ramp test, (b) shear rate of the anodic inks during DIW as a function of printing speed, (c) Pd values calculated for the anodic inks as a function of the printing speed, (d) Pd values calculated for the anodic inks as a function of the inlet pressure, (e) normal force measured during the flow ramp test of the anodic inks, and (f) microscopy image of the AN3 ink flowing out of the nozzle

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Fig. 5

Results of the DIW experiments with anodic inks regarding the printed structure geometry: (a) width and (b) height of the anodic lines as a function of printing speed, (c) the aspect ratio of the anodic lines as a function of the printing speed, (d) flow rate of the AN0 and AN2 inks under various inlet pressures, (e) Pd values calculated for AN0 and AN2 inks under various inlet pressures, and (f) aspect ratio of the AN0 and AN2 lines printed under various inlet pressures

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Fig. 6

Results of the DIW experiments with anodic inks regarding multilayer stacking: (a) cross-sectional profiles of the multilayer AN3 lines, top inset: stereo microscopy image of the ten layer AN3 line, (b) cross-sectional profiles of the multilayer AN0 lines, top inset: stereo microscopy image of the ten layer AN0 line, (c) height/number of layers and (d) width of the anodic lines as a function of number of layer printed, (e) the microscopy image of the AN3 as it is printed, (f) and (g) SEM images of the multilayer AN3 lines, and (h) results of the amplitude sweep of the anodic inks

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Fig. 7

Electrical conductivity and morphology of the printed anodic structures: (a) variation of the electrical resistivity of AN0 and AN3 lines printed under various speeds, (b) statistical distribution of the deformation data obtained from PFQNM characterization of the printed anodic lines, (c) PEO matrix-graphite deformation difference for AN0 and AN3 at two printing speed levels, (d) topography and (e) deformation maps of the AN3 lines printed at 30 mm/s, and (f) topography and (g) deformation maps of the AN3 lines printed at 180 mm/s

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Fig. 8

(a) Optical image showing a set of anodic lines created during the DIW experiments, (b) magnified image of the test lines created to determine the minimum pressure for continuous line printing at 180 mm/s, (c) microscopy image of the electrical measurement configuration for anodic lines highlighting the EGaIn electrodes, (d) microscopy image of an anodic pendant drop used for surface tension measurements, and variation of the viscosity with shear rate for (e) electrolytic inks and (f) anodic inks

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