Adding Konjac Glucomannan for Enhancing the Whole Spraying Performance on Superhydrophobic and Hydrophilic Surfaces

Abstract

Spraying is a common way to coat solutions onto surfaces evenly. Improving spraying effectiveness can avoid wasting solutions and reduce pollution. In this study, a trace amount of natural polysaccharide, konjac glucomannan (KGM), was added into solutions to regulate the spraying performances including the breakup of liquid jets, size of produced droplets, and collision and spreading of droplets on both superhydrophobic and hydrophilic surfaces. The shear viscosity, extensive viscosity, and surface tension of the KGM solutions were tested. The results of spraying experiments showed that adding KGM inhibited the liquid jet from breaking into small droplets, avoided the breakage of droplets on superhydrophobic surfaces, and promoted the spreading of liquid films on hydrophilic surfaces. The numerical simulation showed the stretching of single macromolecules and quantified the energy stored in molecular chains in a shear-dominated flow field during the spreading of droplets on surfaces and an elongationaldominated flow field during the breakage of a liquid bridge. The storage and dissipation of energy during the stretching and relaxing of KMG macromolecules were important origins of the increase in the colloid viscosity and molecular mechanisms of the effect of the KGM additive on spraying performances. This study provided an understanding and a strategy for optimization and application of spraying additives.

A Superhydrophobicity–Slipperiness Switchable Surface with Magneto- and Thermo-responsive Wires for Repelling Complex Droplets

“…As shown in Figure b and Video S2, water droplets cannot rebound (vertically detach) from the surface but continuously slid off, indicating a successful transition from the superhydrophobic surface to the lubricant-impregnated surface by thermoinduced melting of the impregnated paraffin. In fact, we have also tested various complex droplets which remained pinned on conventional superhydrophobic surfaces, such as PAAM-laden , and KGM-laden droplets, and the successful removal of them are demonstrated in Figure S5.…”

“…Moreover, powered by a moving magnetic field, surface impurities can be removed by magneto-responsive wiresexcellent active repellency of impurity. When encountering various complex droplets that remained pinned on superhydrophobic surfaces, − , the 3S surface was heated, and the melted paraffin formed a lubricant layer in between the inclined wires and the complex droplets (a liquid–lubricant–gas system). This led to a continuous removal of various complex droplets under gravitysurface slipperiness.…”

“…The viscoelastic properties of such complex (non-Newtonian) fluids were measured by a rheometer (MCR 102e, Anton Paar, Austria) and detailed in Figure S3, and γ LG was measured by a tensiometer (DCAT 25, DataPhysics, Germany). In addition to water droplets containing PEO, − ,− we also tested various complex liquids made with aqueous solutions of 6 wt % polyacrylamide (PAAM, Macklin, China) , and 2 wt % konjac glucomannan (KGM, Aladdin, China) to demonstrate the wide applicability of 3S surfaces.…”