Submitted to Annual Rheology Reviews, 2005.The progressive break-up of an initially stable fluid column or thread into a
number of smaller droplets is an important dynamical process that impacts many
commercial operations from spraying and atomization of fertilizers and pesticides, to
paint application, roll-coating of adhesives and food processing operations such as
container- and bottle-filling. The progressive thinning of a fluid filament is driven by
capillarity and resisted by inertia, viscosity and additional stresses resulting from the
extensional deformation of the fluid microstructure within the thread. In many
processes of interest the fluid undergoing break-up is non-Newtonian and may contain
dissolved polymer, suspended particles, surfactants or other microstructural
constituents. In such cases the transient extensional viscosity of the fluid plays an
important role in controlling the dynamics of break-up. The intimate connection
between the degree of strain-hardening that develops during free extensional flow and
the dynamical evolution in the profile of a thin fluid thread is also manifested in
heuristic concepts such as âspinnability’, âtackiness’ and âstringiness’. In this review
we survey recent experimental and theoretical developments in the field of capillarydriven
thinning and break-up with a special focus on how quantitative measurements
of the thinning and rupture processes can be used to quantify the material properties of
the fluid. As a result of the absence of external forcing the dynamics of the necking
process are often self-similar and observations of this âself-thinning’ can be used to
extract qualitative, and even quantitative, measures of the transient extensional
viscosity of a complex fluid.NASA, NSF, Schlumberger Foundatio
