In this work we study experimentally the lifetime of oil droplets pressed b
y buoyancy against a large oil/water interface, in a system containing prot
ein (bovine serum albumin). The stability of the drops depends strongly on
their size, which can be explained with the hydrodynamics of thinning of th
e gap region. Two distinct size intervals with different thinning regimes m
ay be discerned: (i) Very small drops (below similar to 20 mu m). They rema
in practically nondeformed up to coalescence; in this case the lifetime dim
inishes with increase of the drop radius. The latter trend may be described
qualitatively in terms of the Taylor law (or mixed Stokes-Taylor law) for
viscous resistance. (ii) Large drops. They form films, and the lifetime ris
es with the increase of the size, which complies with the Reynolds law for
the friction in the gap. The overall dependence of the lifetime on the drop
radius passes through a shallow and broad minimum-here for the first time
this is proved by direct measurement in a real system: only the drop size i
s varied with all other experimental conditions being the same.