Influence of the spring constant of cantilevers on hydrodynamic force measurements by the colloidal probe technique

There is a substantial disagreement in literature on the interpretation of hydrodynamic forces measured with the colloidal probe technique (CPT). While some authors find indications of slip of polar liquids on hydrophilic surfaces (including two of the authors), Honig and Ducker [Phys. Rev. Lett. 98 (2007) 028305] noticed no slip when they used relatively stiff cantilevers. Here, we tested a number of cantilevers with different shapes, dimensions, and spring constants to analyse their influence on hydrodynamic force measurements. In accordance with Honig and Ducker, we show that results obtained with the CPT do not contradict the no-slip boundary condition if the experiments are carried out with stiff cantilevers. The slip lengths inferred from the measurements can be related to the cantilever spring constant, the velocity at which the cantilever is dragged through the liquid, and the viscosity of the liquid. An empirical threshold value is suggested that could help avoiding artefacts.