Self-Limiting Electrospray Deposition on Polymer Templates

Abstract

<p>Electrospray deposition (ESD) applies a high voltage to liquids flowing through narrow capillaries to produce monodisperse generations of droplets down to hundreds of nanometers in diameter, each carrying a small amount of the delivered solute. This deposition method has been combined with insulated stencil masks for fabricating micropatterns by spraying solutions containing nanoparticles, polymers, or biomaterials. To optimize the fabrication process for micro-coatings, a self-limiting electrospray deposition (SLED) method has recently been developed. Here, we combine SLED with a pre-existing patterned polymer film to study SLED’s fundamental behavior in a bilayer geometry. SLED has been observed when glassy insulating materials are sprayed onto conductive substrates, where a thickness-limited film forms as charge accumulates and repels the arrival of additional charged droplets. In this study, polystyrene (PS), Parylene C, and SU-8 thin films of varying thickness on silicon are utilized as insulated spraying substrates. Polyvinylpyrrolidone (PVP), a thermoplastic polymer is sprayed below its glass transition temperature (T<sub>g</sub>) to investigate the SLED behavior on the pre-deposited insulating films. Furthermore, to examine the effects of in-plane confinement on the spray, a microhole array patterned onto the PS thin film by laser dewetting was sprayed with dyed PVP in the SLED mode. This was then extended to an unmasked electrode array showing that masked SLED and laser dewetting could be used to target microscale regions of conventionally patterned electronics.</p>

Determining the Self-Limiting Electrospray Deposition Compositional Limits for Mechanically Tunable Polymer Composites

“…Both of these effects are consistent with our past results with SU-8 possessing higher dielectric constant, but more facile solvent swelling and low glass transition due to the oligomeric nature of the substance. 20 It is interesting to note that the addition of either miscible or immiscible components does appear to stabilize the thickness of the SU-8, which is suggestive that additives offset this sensitivity to solvent.…”

“…We have previously observed that, while SU-8 is sensitive to solvent, its higher dielectric strength leads to it being more self-limiting as a mask material. 20 Taken together with the fact that blending seems to stabilize SU-8 sprays to solvent effects, it follows that adding PS to SU-8 would improve the stability.…”

“…An extension of ESD, coined self-limiting electrospray deposition (SLED) has been demonstrated by only spraying glassy insulating materials below their glass transition temperature (Tg) and mixed with a volatile solvent onto a sufficiently conducting substrate [18][19][20][21][22] . A limited thickness will be achieved as charges accumulate with increased spray time and spray is redirected to uncoated parts of the target.…”

Conformal Silver Films for EMI Shielding of SiP Architectures

“…This effect makes it difficult to build thick, continuous layers on insulators. To address this issue, we utilize a dielectric stencil to focus material to the underlying target substrate [19]- [21]. The stencil is a carefully selected material with a custom orifice that is placed on top of the target, as shown in Fig.…”

Controlling morphology in electrosprayed methylcellulose nanowires via nanoparticle addition: coarse-grained modeling and experiments

“…In addition, the spray of insulating polymers produces thicknesslimited films in which the charge accumulation repels incoming spray droplets. 4,11,12 This self-limiting behavior enables the conformal coating of complex 3D surfaces. 13 Recent work from our group has shown that methylcellulose (MC) forms a selflimiting coating with a unique nanowire architecture when processed by ESD from water : ethanol solutions.…”