Simpkins P G, Kuck V J
Bell Laboratories, Murray Hill, NJ 07974, USA.
J Colloid Interface Sci. 2003 Jul 15;263(2):562-71. doi: 10.1016/s0021-9797(03)00347-3.
A series of experiments that clarify how air bubbles become entrained into coatings are described. The contact line dynamics at the air-liquid interface surrounding a fiber is characterized for a typical coating die operating under atmospheric and pressurized conditions. Glycerin and other viscous liquids are used to reveal that a critical fiber speed exists at which air entrainment begins. The observations confirm that the critical capillary number Ca(c) depends on the physical properties of the coating material, in the form of the Morton number. When the liquid supply is pressurized, the experiments show that adjusting the pressure can stabilize the displaced free surface interface at a prescribed location. Controlling the meniscus location in this way eliminates air entrainment. The threshold occurs when the applied pressure balances the shear exerted on the coating by the moving fiber. Using this approach it is possible to eliminate air entrainment and attain stable wetting at very large values of the capillary number, e.g., Ca congruent with 50.
本文描述了一系列阐明气泡如何混入涂层的实验。对于在大气和加压条件下运行的典型涂布模头，表征了围绕纤维的气液界面处的接触线动力学。使用甘油和其他粘性液体来揭示存在一个临界纤维速度，在该速度下空气夹带开始。观察结果证实，临界毛细管数Ca(c)取决于以莫顿数形式表示的涂层材料的物理性质。当液体供应加压时，实验表明调节压力可以将位移的自由表面界面稳定在规定位置。以这种方式控制弯月面位置可消除空气夹带。当施加的压力平衡移动纤维对涂层施加的剪切力时，就会出现阈值。使用这种方法，可以消除空气夹带并在非常大的毛细管数值下实现稳定的润湿，例如，Ca约为50。
