Electrospray Printing of Polyimide Films Using Passive Material Focusing

Kingsley, Bryce J.; Pawliczak, Emma E.; Hurley, Thomas R.; Chiarot, Paul R.

doi:10.1021/acsapm.1c01073

Cited by 21 publications

(35 citation statements)

References 58 publications

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“…The conductive FTO film is connected to a grounded aluminum base plate using copper tape. Under the influence of a strong electric field, the highly charged particles are directed to grounded surfaces. , The SU-8 photoresist acts as a surface energy pattern to modulate the wetting properties of the substrate, which defines the contact line (and, consequently, the interface geometry) of the target droplet. Additionally, SU-8 is a cross-linked polymer and an excellent electrical insulator.…”

Section: Resultsmentioning

confidence: 99%

Probing Colloidal Assembly on Non-Axisymmetric Droplet Surfaces via Electrospray

et al. 2022

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Microparticles trapped on the surface of a sessile droplet interact via electrostatic and capillary forces. The assembly of colloids at a fluid−fluid interface is governed by particle size, surface chemistry, and contact line roughness. We created nonspherical droplets using surface energy patterning and delivered microparticles to the liquid−air interface with electrospray atomization. Using a water droplet as the target, the particle assembly was observed over time. We found that the underlying surface energy pattern significantly influenced the colloidal assembly and drove particles toward the center of the droplet. The particles were arranged into a single, non-close-packed cluster with local hexagonal ordering but left a clear region with very few particles near the contact line. This depletion region is attributed to long-range electrostatic repulsion from the photoresist used to create the surface energy pattern, which retained electric charge from the electrospray. To understand the effect of electrostatic interactions, we explored target droplets with dissimilar dielectric properties. Using patterned substrates and electrospray for particle deposition, we can harness the assembly of colloids at a fluid interface to build repeatable monolayer patterns.

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Section: Resultsmentioning

confidence: 99%

Probing Colloidal Assembly on Non-Axisymmetric Droplet Surfaces via Electrospray

et al. 2022

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“…The volatility of the carrier solvent, along with the electrospray and environmental conditions, governs the extent of solvent evaporation from the emitted droplets. In many cases (e.g., when using a highly volatile solvent), the solvent evaporates very quickly, resulting in dry (solvent-free) particles or aggregates of material delivered to the target surface. , However, if the solvent does not completely evaporate, the residual is delivered to the target along with the material and dramatically alters the deposited film morphology and microstructure. ,,, We define these two regimes as dry (solvent-free) and partially wet ESD, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Lei et al and Kovacevich et al have shown how electrosprays can be used to deposit polymer surface coatings on complex shapes and 3D-printed lattice structures. , Additionally, conformal coatings can be delivered to micro-scale geometries, such as biological stents . Unlike other deposition techniques, ESD films and coatings are self-limiting and grow nonlinearly due to charge accumulation in the growing film. , This is beneficial for providing uniform film coverage, especially for conformal coatings on intricate surface geometries.…”

Section: Introductionmentioning

confidence: 99%

“…This polymer is an important material for many industrial applications. For example, in electronics manufacturing, it is used for its excellent thermal and dielectric properties. , We have previously reported on the electrospray printing/deposition of polyimide, where we found that passive electrostatic focusing could be used to improve the rate of film growth. However, the efficiency was very low since substantial material was lost to surfaces neighboring the electrospray.…”

Section: Introductionmentioning

confidence: 99%

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Polyimide Films Manufactured Using Partially Wet Electrospray Deposition

Kingsley

Chiarot

2023

ACS Appl. Polym. Mater.

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In electrospray deposition (ESD), solute material is dispersed in a carrier solvent and atomized into a cloud of microdroplets under the influence of a strong electric potential. The volatility, ESD parameters, and environmental conditions determine the rate of solvent evaporation. Complete in-flight solvent evaporation produces dry particles of material that are deposited on the target. In contrast, when the evaporation is incomplete, some residual solvent is delivered with the material. We define these regimes as dry (complete evaporation) and partially wet (incomplete evaporation) ESD. Here, we compare the microstructure and functional characteristics of films deposited in both regimes. We selected polyimide as our solute material given its importance in electronic, health, and environmental applications. An electrospray printhead that provides a tunable solvent evaporation rate via co-flowing air is used to deploy the polyimide. The dry and partially wet regimes can be selected by altering the solution flow rate and the air co-flow rate. Particulate films are formed when the polyimide is delivered to the target dry (solventfree). When solvent is delivered with the polyimide, a dense (partially wet) film is formed on the target. A numerical model of droplet evaporation was developed, which shows the dominant effects of solution flow rate and freestream vapor concentration on the ESD regime. The dry and partially wet films were compared for various functional characteristics including dielectric strength, optical characteristics, and corrosion resistance. For most metrics, the partially wet ESD films outperformed the dry ESD films. Compared to the dry ESD films, the partially wet films had far greater dielectric strength (up to 340 V/μm) and higher optical transparency. Both ESD regimes provided comparable corrosion resistance, which enhanced the reliability of metallic bond joints in an electronics package.

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“…Indeed, the only report of deposition efficiency in near-field templates comes from recent work of Kingsley et al, where they showed that for a still macroscopic (3 mm thick) insulating mask, the deposition efficiency using a SLED compatible material was reported to be less than 5%. 25 All additional material ostensibly found other grounded targets in their spray chamber. Angkawinitwong et al experimented with the coating of microneedle arrays (MNAs).…”

Section: Introductionmentioning

confidence: 99%

Efficient electrospray deposition of surfaces smaller than the spray plume

Park

Liu

D'Souza

et al. 2022

Preprint

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Electrospray deposition (ESD) uses charged droplets at the micro- and nano-scale to create a wide variety of particles and coatings. In ESD, an electrostatic force is applied to a solution, which then disperses charged droplets loaded with the materials to be deposited on a grounded target. Because the droplets carry charge, repulsive effects due to accumulation of charge in a coating (self-limiting electrospray) or “crowding” of the spray droplets can reduce the efficiency of the approach. This is especially the case when the targets are smaller than the characteristic size of the spray plume. For this reason, while many studies have presumed high efficiency in ESD, the actual measured efficiencies for small targets are much lower. Here, it is shown how architecting the local “charge landscape” can lead to ESD coatings approaching 100% deposition efficiency on both flat and microneedle array targets composed of multiple model materials, including biocompatible polymers, proteins, and bioactive small molecules. In this way, ESD can be considered a viable alternative to other conformal approaches, such as dip or inkjet coating.

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Electrospray Printing of Polyimide Films Using Passive Material Focusing

Cited by 21 publications

References 58 publications

Probing Colloidal Assembly on Non-Axisymmetric Droplet Surfaces via Electrospray

Probing Colloidal Assembly on Non-Axisymmetric Droplet Surfaces via Electrospray

Polyimide Films Manufactured Using Partially Wet Electrospray Deposition

Efficient electrospray deposition of surfaces smaller than the spray plume

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