title: Reliable measurements of interfacial slip by colloid probe atomic force microscopy. II. Hydrodynamic force measurements.
abstract: 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.
authors.affiliation: School of Chemistry, F11, The University of Sydney, NSW 2006, Australia.
authors.forename: Liwen
authors.initials: L
authors.lastname: Zhu
authors.forename: Phil
authors.initials: P
authors.lastname: Attard
authors.forename: Chiara
authors.initials: C
authors.lastname: Neto