The behavior of liquid lubricant films on the disk surfaces in magnetic recording is analyzed using the concepts of disjoining and capillary pressure. Particular examples analyzed include lubricant distributions on rough and porous disk surfaces, lubricant flow, and the meniscus force acting on the recording slider sitting on the disk surface.

Application of disjoining and capillary pressure to liquid lubricant films in magnetic recording

The free-surface shape of a liquid in a uniformly rotating cylinder in the presence of surface tension is determined before and after the onset of dewetting at the bottom of the cylinder. Two scenarios of liquid withdrawal from the bottom are considered, with and without deposition of thin film behind the liquid. The governing non-linear differential equations for the axisymmetric liquid shapes are solved numerically by an iterative procedure similar to that used to determine the equilibrium shape of a liquid drop deposited on a solid substrate. The numerical results presented are for cylinders with comparable radii to the capillary length of liquid in the gravitational or reduced gravitational fields. The capillary effects are particularly pronounced for hydrophobic surfaces, which oppose the rotation-induced lifting of the liquid and intensify dewetting at the bottom surface of the cylinder. The free-surface shape is then analyzed under zero gravity conditions. A closed-form solution is obtained in the rotation range before the onset of dewetting, while an iterative scheme is applied to determine the liquid shape after the onset of dewetting. A variety of shapes, corresponding to different contact angles and speeds of rotation, are calculated and discussed.

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The shape of a liquid surface in a uniformly rotating cylinder in the presence of surface tension

Electron beam lithography on uneven resist for uniform Bragg gratings in GaSb based distributed-feedback lasers

Three-dimensional phase diagram for the centrifugal Calcium-alginate microcapsules production technology

Three-dimensional phase diagram for the centrifugal calcium-alginate microcapsules production technology

The mechanisms governing drop formation and detachment from liquid-filled capillaries in a centrifugal field have been studied. Two different systems, the “reservoir-connected” capillary and the “free” capillary, have been modeled and compared. In the former, the capillary is connected to an infinite reservoir of the liquid. In the latter, the capillary is open to the ambient atmosphere on its two ends and is initially full of liquid. Critical rotation speeds for drop detachment have been calculated for various capillary lengths and ratios of the outer to inner radius. Experiments were performed to test some of the theoretical predictions. The results show that for the reservoir-connected system, the drop detaches when it becomes approximately hemispherical, with a radius which is equal to the outer radius of the capillary. The behavior of the free capillary system is more complex and strongly depends on the radii ratio. In general, the free capillary system sustains a pendent drop at equilibrium at higher rotation speeds than the reservoir-connected system.

David K. Boadi

Papers

Drop formation and detachment from rotating capillaries

Equilibrium of a liquid in a rotating groove