The thinning of viscous liquid threads.

The thinning neck of dripping droplets is studied experimentally for viscous Newtonian fluids. High speed imaging is used to measure the minimum neck diameter in terms of the time $\tau$ to breakup. Mixtures of water and glycerol with viscosities ranging from 20 to 363 mPa s are used to model the Newtonian behavior. The results show the transition from potential to inertial-viscous regimes occurs at the predicted values of $\sim$Oh$^2$. Before this transition the neck contraction rate follows the inviscid scaling law $\sim \tau^{2/3}$. After the transition, the neck thinning tends towards the linear viscous scaling law $\sim \tau$.