  The states of gas accumulated at the liquid-solid interface are analyzed
based on the continuum theory where the Hamaker constant is used to describe
the long-range interaction at the microscopic scale. The Hamaker constant is
always negative, whereas the gas spreading coefficient can be either sign.
Despite the complexity of gas, including that the density profile may not be
uniform due to absorption on both solid and liquid surfaces, we predict three
possible gas states at the liquid-solid interface, i.e. complete wetting,
partial wetting and pseudopartial wetting. These possible gas states correspond
respectively to a gas pancake (or film) surrounded by a wet solid, a gas bubble
with a finite contact angle, and a gas bubble(s) coexisting with a gas pancake.
Typical thickness of the gas pancakes is at the nanoscale within the force
range of the long-range interaction, whereas the radius of the gas bubbles can
be large. The state of gas bubble(s) coexisting with a gas film is predicted
theoretically for the first time. Our theoretical results can contribute to the
development of a unified picture of gas nucleation at the liquid-solid
interface.
