Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 149657

149657 - Self-Limiting Electrospray Deposition of Nanoparticle Composites via Sub-Percolation Assembly 

Electrospray deposition (ESD) uses strong electric fields to produce monodisperse droplets from dispersions and solutions that are driven toward grounded targets. Self-limiting electrospray deposition (SLED) is a regime of ESD that achieves controlled targeted coatings by trapping charge in the growing film and redirecting incoming droplets to uncoated areas of the substrate. However, when conductive nanoparticles are added to self-limiting (SL) sprays, the buildup of charge required to repel incoming material becomes disrupted as particle loading increases. This work aims to maximally deliver nanoparticles in the controlled SL regime. Methylcellulose (MC) was chosen as the SL binder due to its ability to form high aspect ratio nanowires, which should increase the interparticle spacing. MC was sprayed in the SLED regime with nanoparticles varying in size, aspect ratio, electrical properties, and surface chemistry at different concentrations. The SL behavior was characterized by measuring the growth of films on 2D patterned gratings and flat wafers. When sprayed, large spherical particles (>200 nm) suppress nanowire formation while smaller particles (<70 nm) are encapsulated. 2D particles, however, still allow for nanowire formation due to field focusing on sharp corners. To determine the SL limit, the MC/nanoparticle blends were sprayed on electrode test patterns of conductive features of varying width (20-240µm) on a silicon wafer with unpatterned areas insulated with 4-5 µm Parylene. In the literature on polymer composites, the bulk conductivity of a composite has been best understood through percolation theory. Consistent with earlier work, particle delivery to the features remained steady below the particle’s percolation limit. Upon reaching the percolation limit, the spray was no longer in the SL regime, causing uncontrolled deposited growth on the features. This percolation limit varies with the conductivity and aspect ratio of the nanoparticle, with silver nanoparticles having the highest conductivity and thus the lowest percolation limit, while a non-conductive nanoparticle such as ITO doesn’t reach its percolation limit even at close to 100 vol%. The percolation limit for the large MXene nanoflakes, small MXene nanoflakes, ITO nanoparticles, was found to be 4.7%, 28%, and above 79% respectively. Silver’s percolation limit was less than 1.2vol%. Pyrolyzing the MC kept the deposited composite morphology porous, while minimally affecting the fine nanoparticle features. When maximally delivering 2D MXene nanoflakes to interdigitated electrodes with 50 μm features, the device showed a 450x increase in capacitance compared to the unfunctionalized device. SLED is unique as a hybrid manufacturing technique on the micron scale because of its scalability, efficiency, flexibility, and ability to be done under ambient conditions.

Presenting Author: Jouan Yu Rutgers University

Presenting Author Biography: Undergraduate Mechanical Engineering Student at Rutgers University.

Authors:

Michael Grzenda 3Spray
Jouan Yu Rutgers University
Maria Atzampou Rutgers University
Christopher Shuck Rutgers University
Yury Gogotsi Drexel Nanomaterials Institute
Jeffery Zahn Rutgers University
Jonathan Singer Rutgers University