Session: 16-02-01: Poster Session: NSF Research Experience for Undergraduates (REU), NSF Posters

Paper Number: 99430

99430 - Non-Destructive Measurement of Optically Scattering Polymer Films Using Image Processing 

Self-limiting electrospray deposition (SLED) has been shown to be a means of creating thin, porous polymeric films conformally on complex 2- and 3D geometries. In this self-limiting regime, glassy insulating materials are sprayed onto conductive substrates, leading to charge accumulation in the film that redirects deposition to uncoated areas. The current challenge in measuring films manufactured through SLED is the high optical scattering. The hollow-sphere morphology causes optical scattering in films composed of otherwise low refractive index materials. Our previous studies have relied on the ease of post-processing of SLED films to measure an equivalent densified thickness: by placing the film in an environment above the glass-transition temperature or by exposing to the film to a favorable solvent environment, the porous morphology collapses into a dense film able to be measured through micro-reflectometry. We note current optical film measurement techniques are only applicable for dense films; or, the technique is destructive or highly-localized in nature (such as scanning electron microscopy (SEM)).

Our previous work has shown that these films can be mechanically tuned by while remaining thickness-limited by selectively incorporating non-self-limiting additives. However, this mechanical testing was limited in scope because the porous thickness of the SLED films could only be measured through micro-reflectometry of post-processed thermally densified samples. Therefore, non-destructive measurement of these films is needed for high-throughput mechanical analysis: samples must remain intact between measurement and mechanical testing. Here, we present a means of automatically and non-destructively measuring the thickness of porous polymeric thin films deposited through SLED.

This technique compensates for the scattering associated with porous films by using image processing on reflection and transmission optical micrographs. The transmission micrograph is used to isolate the film, which is seen in the reflection micrograph, from the background. By using the histogram of oriented gradients method, we determine the principal direction of the film. The film is then segmented using various edge-detection procedures (e.g., Canny). The film thickness and cross-sectional area can then be computed.

A comparative study between cross-sectional SEM (where scattering effects are diminished) and optical microscopy verifies that our optical microscopy technique can be used to consistently, non-destructively measure film thickness. The asymptotic thickness growth of SLED films initially shown through the measurement of thermally densified films is supported by the porous film measurements with the current image processing technique. Additionally, with minimal post processing, porosity can be easily calculated by thermally densifying the film after optical micrographs are taken and measuring the now-dense film using micro-reflectometry.

This work was funded by the NSF through CMMI Award 2019849.

Presenting Author: Noah McAllister Rutgers University

Presenting Author Biography: Noah M. McAllister was born outside of Philadelphia, and is a rising junior studying Aerospace Engineering at Rutgers University. An active member of the Rutgers chapter of the American Institute of Aeronautics and Astronautics (AIAA), Noah currently serves as the chapter President, and served as Judging Chair for the 2021 AIAA Student Conference, as well as the Secretary for the 2021–2022 academic year. He currently is the sub-team lead of the Propulsion Sub-team of RU Airborne, the Rutgers University AIAA Design-Build-Fly competition team. The team won first place for their design proposal in the 2020-2021 competition. Noah has been on the Dean’s List of the School of Engineering his entire college duration. A 2021 NSF REU fellow, Noah currently works in the Hybrid Micro/Nanomanufacturing Laboratory under Dr. Jonathan Singer, where he researches self-limiting electrospray deposition. Additionally, he works in the Digital Manufacturing Lab in the Air Force Research Lab, where he conducts robotic simulations. Following graduation, he intends to pursue graduate studies, with research interests including aerospace applications of thin-film deposition. Noah is an avid clarinetist and played in the Philadelphia Youth Orchestra.

Authors:

Noah McAllister Rutgers University
Maxim Arkhipov Rutgers University
Robert Green-Warren Rutgers University
Assimina Pelegri Rutgers University
Jae-Hwang Lee University of Massachusetts
Jonathan Singer Rutgers University