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Here we report a new study on the boundary conditions for the flow of a simple liquid in a confined geometry obtained by measuring hydrodynamic drainage forces with colloid probe atomic force microscopy (AFM). In this work, we provide experimental data obtained using a best practice experimental protocol and fitted with a new theoretical calculation (Zhu, L.; Attard, P.; Neto, C. Langmuir 2010, submitted for publication, preceding paper). We investigated the hydrodynamic forces acting on a silica colloid probe approaching a hydrophobized silicon surface in a single-component viscous Newtonian liquid (di-n-octylphthalate), a partially wetting system. The measured average slip lengths were in the range of 24-31 nm at approach velocities of between 10 and 80 μm/s. Using our experimental approach, the presence of nanoparticle contaminants in the system can be indentified, which is important because it has been shown that nanoparticles lead to a large apparent slip length. Under our stringent control of experimental conditions, the measurement of the slip length is reproducible and independent of the spring constant of the cantilever.

A simple model of glass-forming liquid modeled via Dzugutov's pair potential is studied by means of the triplet hypernetted chain approximation as formulated by Attard [P. Attard, J. Chem. Phys. 93, 7301 (1990)]. This system, which is known to be mostly dominated by microscopic icosahedral ordering, eludes a correct description in terms of classical two-body integral equation theories. However, it is found here that the simple hypernetted chain approximation when applied at the three-particle level can yield a correct semiquantitative description of both the pair and triplet structure of the supercooled state, capturing features which escape more sophisticated closures implemented on the two-particle level.