Homogeneous Gelation Leads to Nanowire Forests in the Transition Between Electrospray and Electrospinning

Abstract

<p>The morphology of coatings created by electrostatic deposition can be generally divided into three categories: wire mats (electrospinning), particles (electrostatic spray, electrospray deposition(ESD)), and films (all low-viscosity applications). There should exist nanowire forests as a mixture of wire and particulate deposition. Such a morphology has yet to be observed experimentally, which we propose is the result of spatially-varying viscosity in sprayed droplets. We utilized electrostatic dissipative particle dynamics (DPD) and ESD to explore the spray of methylcellulose (MC) in water:ethanol mixtures. MC possesses a lower critical solution temperature (LCST) in water and water:ethanol blends. DPD simulations reveal that the barrier to forming nanowire forests is the directional nature of evaporation, but they should form were evaporation homogeneous. In ESD conducted above the LCST, MC and water phase separate concurrently with the rapid evaporation of ethanol, forming a homogeneous gel phase. This gel can undergo the elongation of electrospinning on a drop-by-drop basis to create forests of individual nanowires. Our study indicates that this homogenous evolution of viscosity is necessary for nanowire forest formation and that the specific viscosity (along with droplet size) further controls the morphology of the forests.</p>

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

“…This method allows the deposition of versatile types of materials at nanograms per droplet into complex 2D and 3D micro-and nanostructures. [4][5][6][7] The relative simplicity and low cost of ESD also aid in the popularity of its use in various applications. Specifically, ESD has been used in the fabrication of microscale electronic devices, drug coating for improved longevity of release characteristics, and the encapsulation of compounds for use in food.…”

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

“…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.…”

“…Each of these parameters significantly impacts the thickness and morphology of thin films produced by SLED. For example, SLED coatings produced by in-air gelation of methylcellulose delivers nanowire SLED coatings as opposed to the rounded morphologies more frequently observed 22 .…”

“…Notably, SLED allows for uniform coatings on complex 3D structures as a post-processing treatment 18 , including 3D printed microlattices 23 and natural structures 22 .…”

“…Other than blending soluble polymers, solids have also been widely added into precursor solutions for spray. We have previously demonstrated that functional nanowires with tunable optical properties can be produced by spraying the composites of plasmonic nanoparticles and that they became better dispersed with the addition of a plasticizer 27 . In fabricating fuel cell electrodes, the spray of blended catalyst particles and electrolytic solutions led to 3D nanostructures with large porosity and high surface area, enhancing the device performance 7,28,29 .…”