  Volatile viscous fluids on partially-wetting solid substrates can exhibit
interesting interfacial instabilities and pattern formation. We study the
dynamics of vapor condensation and fluid evaporation governed by a one-sided
model in a low Reynolds number lubrication approximation incorporating surface
tension, intermolecular effects and evaporative fluxes. Parameter ranges for
evaporation- dominated and condensation-dominated regimes and a critical case
are identified. Interfacial instabilities driven by the competition between the
disjoining pressure and evaporative effects are studied via linear stability
analysis. Transient pattern formation in nearly-flat evolving films in the
critical case is investigated. In the weak evaporation limit unstable modes of
finite amplitude non-uniform steady states lead to rich droplet dynamics,
including flattening, symmetry breaking, and droplet merging. Numerical
simulations show long time behaviors leading to evaporation or condensation are
sensitive to transitions between film-wise and drop-wise dynamics.
