화학공학소재연구정보센터
Langmuir, Vol.30, No.26, 7716-7723, 2014
Solute Concentration-Dependent Contact Angle Hysteresis and Evaporation Stains
The presence of nonvolatile solutes in a liquid drop on a solid surface can affect the wetting properties. Depending on the surface-activity of the solutes, the extent of contact angle hysteresis (CAR) can vary with their concentration and the pattern of the evaporation stain is altered accordingly. In this work, four types of concentration-dependent CAH and evaporation stains are identified for a water drop containing polymeric additives on polycarbonate. For polymers without surface-activity such as dextran, advancing and receding contact angles (theta(a) and theta(r)) are independent of solute concentrations, and a concentrated stain is observed in the vicinity of the drop center after complete evaporation. For polymers with weak surface-activity such as poly(ethylene glycol) (PEG), both theta(a) and theta(r) are decreased by solute addition, and the stain pattern varies with increasing PEG concentration, including a concentrated stain and a mountain-like island. For polymers with intermediate surface-activity such as sodium polystyrenesulfonate (NaPSS), theta(a) descends slightly, but theta(r) decreases significantly after the addition of a substantial amount of NaPSS, and a ring-like stain pattern is observed. Moreover, the size of the ring stain can be controlled by NaPSS concentration. For polymers with strong surface-activity such as poly(vinylpyrrolidone) (PVP), theta(a) remains essentially a constant, but theta(r) is significantly lowered after the addition of a small amount of PVP, and the typical ring-like stain is seen.