The thinning dynamics of a liquid neck before break-up, as may happen when a drop detaches from a faucet or a capillary, follows different rules and dynamic scaling laws depending on the importance of inertia, viscous stresses, or capillary forces. If now the thinning neck reaches dimensions comparable to the thermally excited interfacial fluctuations, as for nanojet break-up or the fragmentation of thermally annealed nanowires, these fluctuations should play a dominant role according to recent theory and observations. Using near-critical interfaces, we here fully characterize the universal dynamics of this thermal fluctuation-dominated regime and demonstrate that the cross-over from the classical two-fluid pinch-off scenario of a liquid thread to the fluctuation-dominated regime occurs at a well-defined neck radius proportional to the thermal length scale. Investigating satellite drop formation, we also show that at the level of the cross-over between these two regimes it is more probable to produce monodisperse droplets because fluctuation-dominated pinch-off may allow the unique situation where satellite drop formation can be inhibited. Nonetheless, the interplay between the evolution of the neck profiles from the classical to the fluctuation-dominated regime and the satellites' production remains to be clarified.critical fluids | singularity formation F or a drop to detach from a capillary or a faucet, the liquid thread connecting them must thin and break. This break-up, or pinch-off, is an example of a singularity with well-established scaling laws and similarity solutions (1-5). Different regimes and scaling laws have been predicted and observed. For small liquid viscosities, the balance between inertia and capillarity leads to the so-called inertial thinning regime, with the thread radius vanishing as time to pinch-off to the power 2/3. When the radius of the thinning thread becomes smaller than the so-called viscous length scale L η ∼ η in 2 =γρ in (where γ, η in , and ρ in are respectively the surface tension, the shear viscosity, and the density of the fluid), viscous forces become important and the neck radius decreases linearly vs. time (1) as RðtÞ = CV η ðt* − tÞ, where V η ∼ γ=η in is a capillary velocity, C is a constant, and t* is the break-up time at neck pinch-off; a viscous time scale can be defined as τ η ∼ L η =V η . Two thinning regimes have been predicted and observed in this case: the so-called viscocapillary regime at low Reynolds numbers exhibiting symmetric necks with C = 0:071 (6) and the viscocapillary-inertial regime emerging when further thinning significantly increases the inner fluid velocity and thus inertia (7). In this latter case, the constant is C = 0:030 and the neck profiles are asymmetric. Note that more recently, other symmetric break-up dynamics have been found for a class of non-Newtonian fluids for which thinning is dictated by the rheological properties of the fluids (8, 9).When the viscosity of the outer fluid is no more negligible, as in the present investigation, ...
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