Search for: All records

Electrospray deposition (ESD) has shown great promise for manufacturing micro- and nanostructured coatings at scale on versatile substrates with complex geometries. ESD exhibits a broad spectrum of morphologies depending upon the properties of spray fluids. Among them are nanowire forests or foams obtained via the in-air gelation of electrospray droplets formed from methylcellulose (MC) solutions. In this study, we explored MC ESD loaded with nanoparticles of various shapes and uncovered the effects of particle fillers on morphology evolution using coarse-grained simulations and physical experiments. Utilizing electrostatic dissipative particle dynamics, we modeled the electrohydrodynamic deformation of particle-laden MC droplets undergoing in-flight evaporation. The simulations quantitatively predict the suppression of droplet deformation as the size or concentration of spherical nanoparticles increases. While small particles can be readily encapsulated into the nanowire body, large particles can arrest nanowire formation. The model was extended to nanoparticles with complex topologies, showing MC nanowires emerging from particle edges and vertices due to curvature-enhanced electric stress. In all cases, strong agreements were found between simulation and experimental results. These results demonstrate the efficacy of the coarse-grained model in predicting the morphology evolution of electrosprayed droplets and lay the groundwork for employing MC nanowires for developing nanostructured composites. 

The diffusion of colloids, nanoparticles, and small molecules near the gas–liquid interface presents interesting multiphase transport phenomena and unique opportunities for understanding interactions near the surface and interface. Stratification happens when different species preside over the interfaces in the final dried coating structure. Understanding the principles of stratification can lead to emerging technologies for materials’ fabrication and has the potential to unlock innovative industrial solutions, such as smart coatings and drug formulations for controlled release. However, stratification can be perplexing and unpredictable. It may involve a complicated interplay between particles and interfaces. The surface chemistry and solution conditions are critical in determining the race of particles near the interface. Current theory and simulation cannot fully explain the observations in some experiments, especially the newly developed stratification of nano-surfactants. Here, we summarize the efforts in the experimental work, theory, and simulation of stratification, with an emphasis on bridging the knowledge gap between our understanding of surface adsorption and bulk diffusion. We will also propose new mechanisms of stratification based on recent observations of nano-surfactant stratification. More importantly, the discussions here will lay the groundwork for future studies beyond stratification and nano-surfactants. The results will lead to the fundamental understanding of nanoparticle interactions and transport near interfaces, which can profoundly impact many other research fields, including nanocomposites, self-assembly, colloidal stability, and nanomedicine.