Influence of liquid miscibility and wettability on the structures produced by drop-jet collisions

TL;DR

This study experimentally investigates how liquid miscibility and wettability influence drop-jet collision outcomes, revealing new fragmentation criteria and the impact of wetting properties on encapsulation structures.

Contribution

It introduces a new dimensionless parameter for drop fragmentation and highlights the critical role of wettability in drop encapsulation during collisions.

Findings

Drop encapsulation occurs when jet surface tension is lower than drop surface tension.

A new dimensionless parameter successfully predicts drop fragmentation across liquids.

Total wetting prevents drop encapsulation, limiting certain applications.

Abstract

Collisions between a stream of drops and a continuous jet of a different liquid are experimentally investigated. In contrast to previous studies, our work focuses on the effects of liquid miscibility and wettability on the collision outcomes. Thus, miscible and immiscible liquids providing total and partial wetting are used. We show that, as long as the jet surface tension is smaller than the drop surface tension, the drops can be encapsulated by the jet, providing the so-called drops-in-jet structure. The transitions between the different regimes remain similar in nature with a capillary fragmentation responsible for the jet break-up and an inertial fragmentation causing the drops (and then possibly the jet) to break up. The dimensionless numbers proposed in the literature to model the inertial fragmentation thresholds do not bring the results obtained with different liquids at the same critical value. We explain the reason via a detailed analysis of the collisions, accounting for the drop and jet extensions and their kinetics. The drop fragmentation is found to occur during the recoil phase, leading us to propose a new dimensionless parameter that successfully reproduced all our experimental data obtained with immiscible liquids. Finally we demonstrate that the most dramatic change of the collision outcomes is produced by using drops that totally wet the jet. In this case, the encapsulation of the drops cannot be achieved, constituting a true limit to some applications based on the solidification of the drops-in-jet structure.