【摘要】 目的用毛细管投影传感技术(MPCP)定量表征经典生物材料表面的液固界面摩擦力,揭示滚动角测试所无法揭示的液固界面作用规律。方法利用毛细管投影传感技术(MPCP)表征了水滴在荷叶、玫瑰花瓣和蝴蝶翅膀表面的摩擦力,并进一步探讨了样品干燥、水滴大小和移动速度对液固摩擦力的影响规律。结果当液滴体积由2μL增大到10μL时,水滴在新鲜荷叶表面的静摩擦力F_S从(10.01±0.75)μN增大到(15.99±1.99)μN,动摩擦力F_K由(9.10±1.30)μN增大到(11.31±0.75)μN;干燥过程使得FS由(22.11±3.44)μN上升到(34.72±1.99)μN,F_K由(10.40±0.75)μN增大到(20.42±3.00)μN。与荷叶不同的是,新鲜玫瑰花瓣的静摩擦力F_S和动摩擦力F_K均高于冻干玫瑰花瓣,且随着水滴尺寸的增大而明显增大。由于蝴蝶翅膀结构的各项异性,顺着蝴蝶翅膀D_F方向的F_S和F_K比反向D_O方向要明显小一些,有利于水滴从体表滚落。当液滴移动速度由0.05mm/s增大到2.05mm/s时,荷叶表面的F_S和F_K变化不明显;新鲜玫瑰花瓣的F_S由(70.22±1.99)μN减小到(60.21±1.99)μN,F_K由(44.21±2.25)μN显著减小到(18.21±1.30)μN。而冻干玫瑰花瓣表面的F_S和F_K,随着液滴移动速度的增大而略微减小。蝴蝶翅膀的摩擦力对液滴移动速度表现出一定的方向依赖性,随着液滴移动速度的增大,D_F向的F_S和F_K保持恒定,而D_O向的F_S和F_K减小则显著一些。结论用毛细管投影传感技术MPCP可以揭示水滴在固体表面的摩擦特征,定量表征摩擦力,弥补了滚动角只能表征液滴滚落一瞬间固体对水滴滑动的阻力,无法表征液固动摩擦的不足;定量地揭示了样品干燥、水滴大小和移动速度对水滴在荷叶、玫瑰花瓣和蝴蝶翅膀表面摩擦力的影响规律。更多还原

【Abstract】 Contact angle and sliding angle are usually used to characterize the wettability of solid surfaces, though the technique has its own inherent limitations. In the current work, a newly established technique for the measurement of liquid-solid interfacial friction is employed to quantitatively characterize the classical biological surfaces with superwettabilities, including lotus leaves, rose petals and butterfly wings. The liquid-solid friction forces of these classical surfaces are characterized by the technique of MPCP(monitoring the projection of capillary position). The influences of sample drying, size and moving velocity of water droplet on the liquid-solid friction force are also discussed. When the droplet volume is increased from 2 μL to 10 μL, the static friction force, F_S, of fresh lotus leaves increases from(10.01±0.75) μN to(15.99±1.99) μN, while the kinetic friction force, F_K, slightly increases from(9.10±1.30) μN to(11.31±0.75) μN. The drying process increases both the F_S and F_K of lotus leaves that F_S increases from(22.11±3.44) μN to(34.72±1.99) μN, and F_K increases from(10.40±0.75) μN to(20.42±3.00) μN upon the increase of droplet volume. Different from lotus leaves, both F_S and F_K of rose petals increase significantly upon the droplet-volume increase, and are larger than that of the dried ones. Due to the anisotropic structures on butterfly wing, F_S and F_K along the DF direction of butterfly wings are significantly smaller than that along DO direction, facilitating the rolling off of water droplets. When the moving speed of the droplet increases from 0.05 mm/s to 2.05 mm/s, F_S and F_K do not change obviously; in contrast, F_S of fresh rose petals decreases from(70.22±1.99) μN to(60.21±1.99) μN, and F_K significantly decreases from(44.21±2.25) μN to(18.21±1.30) μN, while F_S and F_K of dried rose petals slightly decreases. The velocity dependence on butterfly wings shows directional dependence that F_S and F_K along D_F direction are almost constant and significantly decreased in the opposite direction D_O. The MPCP technology has the capability to reveal all the detailed features of a friction process and to quantitatively characterize the wettability of solid surfaces. It overcomes the drawbacks of the measurement of sliding angle which measures the instant force when water droplet starts to sliding. Moreover, the quantitative characterization of the influences of the sample drying, size and moving velocity of water droplet on the liquid-solid friction force is helpful to reveal the scientific rules that cannot be revealed by the tests of contact angle and rolling angle.更多还原