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

Abstract

Electrospray deposition (ESD) is a versatile micro-/nanocoating technology that utilizes the competition between the surface charge of a droplet and its surface tension to create monodisperse generations of micro-/nanodroplets. ESD can deposit uniform thin films by including dilute solutes in these droplets. One mode of ESD, self-limiting ESD (SLED), has been shown to exist when glassy polymers are sprayed in a volatile solvent below the polymer glass-transition temperature (T g). This leads to charge accumulation on the coating surface that slows the growth of the film thickness. Since solutes can be easily blended in dilute ESD solutions, we investigate the SLED limits of self-limiting and non-self-limiting solute blends. As a motivating application, we focus on the mechanical properties of the films. Specifically, we blend self-limiting polystyrene and SU-8 epoxy resin with different non-self-limiting mechanical modifiers, such as plasticizers and curing agents. To characterize the resulting morphologies and mechanical properties, we employ scanning electron microscopy and nanoindentation of the as-received porous and thermally smoothed films. The results illustrate the formation of composited polymers that exhibit self-limiting ability by SLED, depending on the interaction between the two components. Furthermore, mechanical properties could be effectively fine-tuned within these compositional ranges. This signifies that the 3D coating capabilities available through SLED can be enhanced by incorporating additional functionalities and properties beyond the base matrix.

Sub‐Micron Thickness Self‐Limiting Electrospray Deposition via Voltage Bias of Spray Target

“…[1] These droplets form due to competing interactions between surface tension and Coulombic repulsions. [2][3][4][5] ESD has been employed in several application areas, ranging from semiconductors to biotechnology, [6][7][8][9][10][11][12] as this process shows great promise as an emerging technology for surface coating applications. [1][2] With respect to photovoltaics and drug delivery, DOI: 10.1002/admi.202300982 ESD is particularly appealing for thin film coatings as it can effectively limit material loss as well as its facile production.…”

Viscoelastic properties of electrospray-deposited polymer shells via quartz crystal microbalance with dissipation (QCM-D)

“…[1][2][3][4] ESD is a technique notable for its ability to generate uniform polymer films with tunable morphologies. [5][6][7][8] Tunability, i.e., fine control of the microstructure, thickness, and porosity is achieved through manipulation of the electrospray parameters, such as input voltage, polymersolvent concentration, separation distance, and solution conductivity. 5,9 In the self-limiting electrospray deposition (SLED) regime, electrostatic charge build-up leads to the formation of conformal micron-scale porous coatings on 2D and 3D surfaces.…”

“…[5][6][7][8] Tunability, i.e., fine control of the microstructure, thickness, and porosity is achieved through manipulation of the electrospray parameters, such as input voltage, polymersolvent concentration, separation distance, and solution conductivity. 5,9 In the self-limiting electrospray deposition (SLED) regime, electrostatic charge build-up leads to the formation of conformal micron-scale porous coatings on 2D and 3D surfaces. 4,6,10 The ability of SLED to coat both conductive and non-conductive surfaces is highly advantageous for coating various materials, with past and current examples including, most commonly, metals and semiconductors, but also glass, hydrogels, living tissue, and gold plated quartz.…”

“…In our previously published report of the mechanical characterization of SLED films, we demonstrated the effects of film morphology on the quasistatic mechanical response of SLED films using various model polymers. 5 Nanoindentation with a conospherical tip was used to evaluate SLED film response to compressional loads at low strain-rates. Further, laser induced projectile impact test (LIPIT) is often utilized to evaluate a materials ability to dissipate the energy of high speed impact using ceramic or polymer based microprojectiles, 3-30 µm in diameter.…”

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

“…In addition, the spray of insulating polymers produces thickness-limited 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 self-limiting coating with a unique nanowire architecture when processed by ESD from water : ethanol solutions.…”