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

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 elongational-dominated 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.