Cavity dynamics after the injection of a microfluidic jet in capillary bridges

TL;DR

This study investigates cavity formation and collapse in capillary bridges caused by microfluidic jets, analyzing how material properties and wettability influence bubble entrapment and jet dynamics for applications like needle-free injections.

Contribution

It provides a comprehensive analysis of cavity dynamics across different materials and wettability conditions, including modeling impact velocities and collapse behaviors.

Findings

Agarose gels with storage modulus below 176 Pa behave like liquids during impact.

Different cavity collapse types affect bubble size and number.

Wettability influences the formation of Worthington jets and energy dissipation.

Abstract

The impact of solid and liquid objects (projectiles) onto liquids and soft solids (targets) generally results on the creation and expansion of an air cavity inside the impacted objects. The dynamics of cavity expansion and collapse depends on the projectile inertia as well as on the target properties. In this paper we study the impact of microfluidic jets generated by thermocavitation processes on a capillary bridge between two parallel planar walls. Different capillary bridge types were studied, Newtonian liquids, viscoelastic liquids and agarose gels. Thus, we compare the cavity formation and collapse between a wide range of material properties. Moreover, we model the critical impact velocity for a jet to traverse a capillary bridge type. Our results show that agarose gels with a storage modulus lower that 176 Pa can be modelled as a liquid for this transition. However, the predicted transition deviates for agarose gels with higher storage modulus. Additionally, we show different types of cavity collapse, depending on the Weber number and the capillary bridge properties. We conclude that the type of collapse determines the number and size of entrained bubbles. Furthermore, we study the effects of wettability on the adhesion forces and contact line dissipation. We conclude that upon cavity collapse, for hydrophobic walls a Worthington jet is energetically favourable. In contrast, for hydrophilic walls, the contact line dissipation is in the same order of magnitude of the energy of the impacted jet, suppressing the Worthington jet formation. Our results provide strategies for preventing bubble entrapment and give an estimation of the cavity dynamics for needle-free injection applications and additive manufacturing among other applications.