Humidity influences the adhesion between the surfaces of hydrophilic particles. One reason is
capillary condensation. Under ambient conditions, water condenses into the gaps between neighboring
particles. Such a water meniscus causes an attrac¬tive force, called capillary force. Several aspects of
capillary forces are analyzed experimentally and theoretically:
Capillary forces of hydrophilic particles sensitively depend on the surface structure on the
0.5 nm scale. As a result, surface roughness has a drastic effect. A simple, approximate formalism
was developed to take surface roughness and heterogeneity into account when calculating capillary
- Butt, H.-J.: Capillary forces: Influence of roughness and heterogeneity. Langmuir 2008, 24, 4715-4721.
- Butt, H.-J. & M. Kappl: Normal capillary forces. Adv. Colloid Interface Sci. 2009, 146, 48-60.
Measurement of capillary forces by colloid probe experiments allows to characterize certain properties of
thin liquid films, such as the film thickness, the viscosity and the surface tension.
Ally, J., E. Vittorias, A. Amirfazli, M. Kappl, E. Bonaccurso, C.E. McNamee & H.-J. Butt:
Interaction of a microsphere with a solid supported liquid film. Langmuir 2010, 26, 11797-11803.
Capillary forces between soft elastic surface are stronger than between relatively stiff surfaces.
The capillary force was calculated and a criterion is suggested to distinguish between soft and stiff.
Butt, H.-J., W.J.P. Barnes, A. Del Campo-Becares, M. Kappl & F. Schoenfeld:
Capillary forces between soft, elastic spheres. Soft Matter 2010, 23, 5930-5936.
Strong electric fields enhance capillary condensation. A generalized Kelvin equation has been
derived to quantify this phenomenon. It is relevant for scanning tunneling microscopy and various
AFM based nanolithographies.
Butt, H.-J., M. Untch, A. Golriz, S.A. Pihan & R. Berger: Electric field-induced condensation:
An extension of the Kelvin equation. Phys. Rev. E 2011, 83, 061604.