  The effective dilatational and shear viscosities of a particle-laden fluid
interface are computed in the dilute limit under the assumption of an
asymptotically vanishing viscosity ratio between both fluids. Spherical
particles with a given contact angle of the fluid interface at the particle
surface are considered. A planar fluid interface and a small Reynolds number
are assumed. The theoretical analysis is based on a domain perturbation
expansion in the deviation of the contact angle from $90^\circ$ up to the
second order. The resulting effective dilatational viscosity shows a stronger
dependence on the contact angle than the effective shear viscosity, and its
magnitude is larger for all contact angles. As an application of the theory,
the stability of a liquid cylinder decorated with particles is considered. The
limits of validity of the theory and possible applications in terms of
numerical simulations of particle-laden interfaces are discussed.
