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.

Hydrodynamic force measurements under precisely controlled conditions: Correlation of slip parameters with the mean free path

“…Slip and accommodation can vary significantly over surfaces due to local fluctuations in interface properties. In good agreement with the reports of other authors, 29,62 we find that slip parameters generally differ by roughly 10% for measurements on distinct spots on the same substrate. We therefore propose that experiments aiming to investigate the dependence of slip on gas properties are being conducted (1) without lateral displacement of the surfaces relative to each other, (2) as local (with small areas) as possible, and (3) with a good characterization of the interfaces at the very position of the measurements.…”

“…29,62 Note that this variation between results obtained on different spots is larger by a factor ∼10 than the error in the determination from the fit. This finding confirms the strong dependence of hydrodynamic forces on the local details of the interface and suggests that in experiments with inherent averaging due to large surface areas (such as flow measurements with micro-channels) correlations between parameters may possibly be weak or not visible.…”

Techniques for physicochemical characterization of nanomaterials

“…The oscillating cantilever then scans over the surface of specimen to generate an image with a vertical resolution of around 0.5 nm (Tiede et al, 2008; Zhu et al, 2011). Like SEM and TEM techniques, AFM can be used for investigating the size, shape, structure, sorption, dispersion and aggregation of nanomaterials — the different scanning modes employed in AFM studies include noncontact mode (also called static mode), contact mode and intermittent sample contact mode (also called dynamic mode and tapping mode) (Hinterdorfer et al, 2012; Mavrocordatos et al, 2004; Picas et al, 2012; Sapsford et al, 2011; Song et al, 2011).…”

Casimir and hydrodynamic force influence on microelectromechanical system actuation in ambient conditions

“…Although other expressions for f à have been used in various studies depending on the nature of interacting surfaces, 17,[19][20][21][22][23][24][25] our tests indicated that the physical results remain qualitatively the same as those obtained with Eq. (2).…”

“…Several works indicated that the slip length depends on the morphology and material of the solid surface. [16][17][18][19][20][21][22][23] Nevertheless, it remains unexplored how the interplay of Casimir forces and hydrodynamic dissipation can affect actuation dynamics of MEMS/NEMS, and we consider this below. The modulation of the magnitude of the Casimir forces can also alter the interplay between dissipation and stiction dynamics, and for this aspect we consider PCMs, where the optical properties alter drastically during amorphous-crystalline phase transitions.…”