We investigate the effects of inertia on the hydrodynamics in the microscopic vicinity of moving contact lines. These hydrodynamics control the macroscopic shape and spreading of fluid bodies across solid surfaces. We perform experiments at low capillary number (Ca<0.1) and negligible (10−4) to moderate (Re∼1) Reynolds number. On a microscopic scale, inertia decreases the dynamic curvature of the free surface near the contact line compared to the case with Re=0 at the same Ca. On a macroscopic scale, inertia lowers the apparent contact angle of the static-like macroscopic interface compared to the situations with the same Ca but negligible Re.

We explore the effects of thin films on the hydrodynamics of macroscopic fluid bodies spreading over solid surfaces. To examine these effects, we measure the interface shape within microns of moving contact lines and compare those measurements to two asymptotic models in the limit of small capillary number, Ca. One model requires that the films affect the hydrodynamics only in a microscopic region near the contact line and allows the macroscopic meniscus to exhibit a nonzero effective contact angle. The other model describes the film as containing mobile fluid and specifically models the flow as fluid moves into or out of the film as the contact line moves. We examine fluids advancing and receding on wetting and nonwetting surfaces with spontaneously forming (molecular scale) and pre-existing (micron scale) films. Our results emphasize the importance of the mobility of the molecules in these very thin films in determining the hydrodynamics governing the moving contact line. The first model, which describes fluids advancing over dry surfaces, also accounts for the hydrodynamics of liquids advancing over very thin, immobile films. Surprisingly, the same model fails when fluid recedes on a nonwetting surface and no film is present. For mobile pre-existing films, the second model, based on Landau and Levich’s theory, accounts for the hydrodynamics in the limit of small Ca.

No abstract

No abstract

We have successfully demonstrated longitudinal recording at areal density of 130 Gb/in2 at a data rate as high as 170 Mbps (21 MB/s) and at a bit-aspect-ratio (BAR) of 2.9, using merged inductive-write/spin-valve-read heads on low noise thin film disks. The heads were fabricated with the standard photolithography and wafer pole trimming used in our currently available commercial products. The reader is a bottom synthetic spin valve (BSSV) with a 0.09 μm gap, and the writer has a conventionally trimmed pole with 0.09 μm gap. The reader magnetic read width (MRW) was measured at 0.10 μm. At read bias of ∼4 mA we measured reader sensitivity as high as 20 mV/μm. The write head was also optimized for tracks as narrow as 0.14 μm operating at overwrite (OW) of 36 dB and nonlinear transition shift (NLTS) better than −25 dB at 610 kBPI, without precomp. Using conventional media we measured total spectral SNR∼18 dB. The media to electronics noise ratio was 4.8, showing that we are still operating in a media noise limited system. Low-flying air bearing surface (ABS) design and advanced pole tip recession (PTR) control were required to achieve magnetic spacing of about 15 nm.