| dc.description.abstract | This study contains two topics: atypical liquid-infused surface and meniscus-induced motion of tiny objects.
Part I - Atypical liquid-infused surface
Atypical liquid-infused surfaces (ALIS) which demonstrate very high bubble/drop angles (> 160o) and ultra-low contact angle hysteresis (CAH < 2o) have been facilely fabricated. Porous hydrophilic nano-filtration membrane and hydrophobic stretched polytetrafluoroethylene film were submerged in water (water-infused surface) and in decane (alkane-infused surface), respectively. The air bubble/liquid drop (2 L) can move with ease on ALIS in submerged conditions at a low tilted angle of 2o. The rolling motion of a water drop is observed, similar to its motion on superhydrophobic surface. It is known that the addition of surfactants can reduce the interfacial tensions of water drop and intensifies CAH of water drop on superhydrophobic surfaces. But it has negligible effects on wetting properties of ALIS. In the presence of surfactant, the fluid particle moves readily on ALIS but its velocity exhibits a non-monotonic variation with surfactant concentrations due to surface remobilization. Mechanically damaged ALIS demonstrates the self-healing ability of its wetting properties and preserves the particle motion even at low inclination.
Part II - Meniscus-induced motion of tiny objects
In nature, some water-walking insects have developed the meniscus-climbing technique depended on surface tension. They ascended by fixing their body posture without moving their legs. In this work, the effects of floating particle shape and meniscus curvature on the meniscus-ascending behavior are explored. The flat particles with millimeter-size are made of polyethylene terephthalate (PET) sheets, and their shapes vary from triangle, square, to rectangle. Three types of menisci are considered, including pendant drop, liquid bridge, and sessile drop. For particles with triangular and square shapes, they tend to slide down and stay at the bottom of menisci because the gravitational force wins over the capillary force. However, the rectangular sheet is able to climb the meniscus surface due to uneven lateral capillary force. The meniscus curvature of its equilibrium position is close to zero, but the upward capillary force balances the particle weight. Next, we replace PET sheet with smaller flaky aluminium powder and put it on the surface of menisci. The result show the powder will spread and cover the meniscus rapidly. | en_US |