Ambient electrostatic deposition has been widely used industrially, such as in automotive painting. Based on the different dynamic viscosity of deposited materials during processing, the morphology of coating surface from electrostatic deposition can be generally divided into three categories: wire mats (electrospinning), particles (electrostatic spray, electrospray deposition), and films (all low-viscosity applications). At intermediate regimes between electrospinning and electrospray, 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. To investigate this mechanism, we utilized electrospray deposition (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. Above the LCST, MC and water phase separate concurrently with the rapid evaporation of ethanol, forming a shear-thickening, homogeneous gel phase. This gel can undergo the elongation of electrospinning on a drop-by-drop basis to create forests of individual nanowires. To verify this mechanism, we employed different viscosities of MC by ESD through changes in (1) molecular weight, (2) loading concentration, and (3) additive content. The results reveal that lowering the viscosity of the gel increases the aspect ratio of formed nanowires. Similarly, the incorporation of additives and volatile additives that lead to too high or too low a viscosity prevents the formation of nanowires in ESD. Our study indicates that the homogenous evolution of viscosity is necessary for nanowire forest formation and that the specific viscosity further controls the morphology of the forests. Moreover, obtaining a wide nanowire forests with low-temperature spray possesses high potential for scalable manufacturing processing of nanowires on a variety of 3D surfaces.

Electrospray deposition of nanowire forests through spinodal gelation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.