  We investigate the deformation of elastic microcapsules adsorbed at
liquid-liquid interfaces. An initially spherical elastic capsule at a
liquid-liquid interface undergoes circumferential stretching due to the
liquid-liquid surface tension and becomes lens- or discus-shaped, depending on
its bending rigidity. The resulting elastic capsule deformation is
qualitatively similar, but distinct from the deformation of a liquid droplet
into a liquid lens at a liquid-liquid interface. We discuss the deformed shapes
of droplets and capsules adsorbed at liquid-liquid interfaces for a whole range
of different surface elasticities: from droplets (only surface tension)
deforming into liquid lenses, droplets with a Hookean membrane (finite
stretching modulus, zero bending modulus) deforming into elastic lenses, to
microcapsules (finite stretching and bending modulus) deforming into rounded
elastic lenses. We calculate capsule shapes at liquid-liquid interfaces
numerically using shape equations from nonlinear elastic shell theory. Finally,
we present theoretical results for the contact angle (or the capsule height)
and the maximal capsule curvature at the three phase contact line. These
results can be used to infer information about the elastic moduli from optical
measurements. During capsule deformation into a lens-like shape, surface energy
of the liquid-liquid interface is converted into elastic energy of the capsule
shell giving rise to an overall adsorption energy gain by deformation. Soft
hollow capsules exhibit a pronounced increase of the adsorption energy as
compared to filled soft particles and, thus, are attractive candidates as foam
and emulsion stabilizers.
