This work stands apart: the nearest neighbors study drops, but from other angles: whole elastic drops, solution spreading on glass, rain and microplastics, and time crystals. Here, the focus is on the breakup of a liquid filament with surface rheology, which is closer to classical hydrodynamics than to neighboring topics. Previous attempts to suppress satellite drops either required complex equipment (active methods with waveform optimization) or changed bulk viscosity or viscoelasticity, which narrowed the operating window and risked clogging nozzles. Surfactants were known to influence filament breakup, but low-molecular-weight surfactants only slowed thinning and did not fully eliminate satellites. Macromolecular surfactants such as proteins form a gel-like layer with its own viscoelasticity, but experimental evidence of their ability to completely remove satellite drops was lacking.
Experiments were conducted with aqueous solutions of bovine serum albumin (BSA) in NaCl buffer. Protein concentration was varied from 0.001 to 5 g/L, and surface aging time from 100 to 600 seconds, to control the degree of adsorption and thus surface viscoelasticity. A cylindrical filament with a radius of 0.32 mm and a length of about four radii was clamped between two blunt needles, held for a set time to allow the protein layer to form, then slowly stretched to induce quasi-static thinning and breakup. The process was recorded with a high-speed camera. Surface tension was measured using the pendant drop method, surface shear rheology with a rotational rheometer equipped with a double-ring module in oscillatory mode, and surface dilatational rheology using the oscillating pendant drop method. To rule out Marangoni effects, control experiments were performed with the low-molecular-weight surfactant sodium dodecylbenzenesulfonate (SDBS) up to its critical micelle concentration. Additionally, a one-dimensional theoretical model was constructed, including continuity, Navier-Stokes, and surface stress equations based on the Boussinesq-Scriven model, and solved numerically using a finite-difference method with a fifth-order WENO scheme.
At a BSA concentration of 0.001 g/L, the filament breaks just like a pure liquid: the radius minimum shifts toward the two filament-bead transitions, forming a double neck that pinches off a satellite drop. But already at 0.1 g/L, the neck remains at the filament center until breakup, and satellite drops disappear completely. The Ohnesorge number in all experiments was 0.006-0.008, meaning the flow was nearly inviscid, so the suppression cannot be explained by bulk effects. Control experiments with SDBS showed behavior indistinguishable from the pure liquid, ruling out Marangoni stresses. Surface rheology measurements revealed that the surface shear viscosity of BSA at a characteristic frequency of 100 Hz reaches the order of $10^{-2}$ mPa·s·m, three orders of magnitude higher than that of low-molecular-weight surfactants. The surface dilatational elastic modulus was 50-70 mN/m. Numerical simulations reproduced the elimination of satellites and showed that at the late stage of thinning, the surface shear viscous force balances the capillary force, suppressing the inertial nonlinear effects that, in a pure liquid, shift the point of maximum thinning away from the center. This keeps the fastest-thinning point at the filament center, preventing the formation of a double neck. Dilatational elasticity plays a secondary role: it shortens the filament and prevents the emergence of new necks. For the neck radius near breakup, a scaling law was derived: the minimum radius is proportional to the time to breakup divided by the surface Ohnesorge number.
This work differs from neighboring studies in that it is the first to experimentally demonstrate complete elimination of satellite drops via surface viscoelasticity, rather than bulk rheology or active control. Neighboring studies dealt with drops bouncing off whole, spreading on glass, or launching microplastics via rain; here, the focus is on filament breakup with a surface protein layer, which is new for this group. The theoretical model and scaling law provide a quantitative explanation that was previously missing. This fills the gap between theory, which predicted the dominance of surface viscosity, and experimental data.
The topic could evolve toward more complex surface rheologies: mixed protein layers, particles, polymers. It may be possible to study the influence of surface viscoelasticity on other breakup topologies: drops in collisions, bubbles, jets. Extending the model to three-dimensional flows and accounting for non-equilibrium adsorption is promising. From a practical standpoint, optimizing concentrations and aging times for specific industrial liquids is of interest.
The results could directly affect inkjet printing, microfluidics, bioprinting, and extreme ultraviolet lithography, where satellite drops degrade quality and contaminate equipment.
The next step will be to test the approach on real printheads and inks, as well as to investigate the long-term stability of protein layers under industrial conditions.
In the hydrodynamics of free surfaces, the precise role of different components of surface viscoelasticity (shear and dilatational) in the pinch-off singularity remains an open question. This work shows that surface shear viscosity dominates at the late stage, but a complete picture for arbitrary rheologies has yet to be constructed.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study experimentally and numerically investigates the suppression of satellite droplets during the breakup of a liquid thread with an adsorbed layer of bovine serum albumin. It is shown that surface viscoelasticity, primarily the shear viscosity, holds the thread neck at the center and completely eliminates satellite formation. A scaling law for self-similar thinning is derived and confirmed by simulations.
Where its strength is
This work provides a direct experimental and theoretical mechanism for passive suppression of satellite droplets via surface rheology, without altering the bulk properties of the liquid. This paves the way for simple control of thread breakup in microfluidics and inkjet printing.
Where it could go next
Worth trying
Why this may matter
If the mechanism proves universal across different surface-active macromolecules, it would offer a simple and inexpensive way to eliminate defects in inkjet printing, bioprinting, and microfluidic devices without complex equipment.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.51, against a usual 0.64. It looks like few have drilled nearby.
Adding protein at a concentration of just 0.02-0.1 grams per liter (20-100 parts per million) completely eliminates satellite drops, which is comparable to dissolving a pinch of egg powder in a bucket of water.