  An object withdrawn from a liquid bath is coated with a thin layer of liquid.
Along with the liquid, impurities such as particles present in the bath can be
transferred to the withdrawn substrate. Entrained particles locally modify the
thickness of the film, hence altering the quality and properties of the
coating. In this study, we show that it is possible to entrain the liquid alone
and avoid contamination of the substrate, at sufficiently low withdrawal
velocity in diluted suspensions. Using a model system consisting of a plate
exiting a liquid bath, we observe that particles can remain trapped in the
meniscus which exerts a resistive capillary force to the entrainment. We
characterize different entrainment regimes as the withdrawal velocity
increases: from a pure liquid film, to a liquid film containing clusters of
particles, and eventually individual particles. This capillary filtration is an
effective barrier against the contamination of substrates withdrawn from a
polluted bath and finds application against biocontamination.
