Droplet Coalescence Study

Date: July 2022

National Institute for Lasers, Plasma and Radiation Physiscs | Romania | Laser Department

Mihai Boni, Scientific Researcher

The optofluidic application in which Hamilton products will be used is the study of droplet coalescence. These experiments will be carried out on Earth at 1g, as well as in microgravity, in a series of parabolic flights, in which an aircraft performs a series of maneuvers, called parabolas. Each parabola provides up to 22 seconds of reduced gravity or weightlessness, during which time scientists can perform experiments and obtain data on the coalescence of microliter droplets that would not otherwise be possible on Earth.

The Parabolic Flight experiment, which will be deployed in October 2022, is designed to test some of the key design solutions of the setup proposed in the ESA-HRE-ESR-DropCoal project "Setup for investigation of drops coalescence in view of medical applications" of the European Space Agency (ESA), which our group is coordinating and with deployment in 2023. The project aims to study drop coalescence and the mixing of two drops after coalescence under microgravity conditions on the International Space Station (ISS). ESA ISS DropCoal project focuses on the approach of two drops and the first moments of drop coalescence with high temporal and spatial resolution. The ESA project enables the investigation of coalescence and droplet mixing through the long-term microgravity conditions available on the ISS. The coalescence of two droplets will be measured for three types of liquids under microgravity conditions: ultrapure water, a solution of a marker (methylene blue) in water and a solution of 20% ethyl alcohol in water.

The experiment itself is dedicated to making measurements on the rebound, coalescence, and separation mechanisms of two droplets with diameters between 2 and 5 mm. These mechanisms are determined by the kinetic and geometric parameters of each collision, as well as by the properties of the liquids in the droplets (nature of the liquids, particular droplet diameters, stability of spherical shapes and diameters, refractive indices) and of the surrounding gas/medium. These are key elements of the experiment, due to their role in droplet generation, where they must ensure good stability and reproducibility after several repetitions of the following operations: coalescence of droplets, aspiration of liquid droplets and cleaning of droplet needles.

To test different needles in microgravity, we intend to build an experimental device containing three 10 ml syringes (automatically and simultaneously operated) and 9 needles. The syringes must have a small dead volume, as all other components will add a relatively large amount of dead volume to the system. Due to safety regulations, the pump and syringes will be mounted in a different enclosure than the needles.

Receiving the syringe grant will solve one of the project's sticking points, as the Hamilton syringes meet ESA-mandated safety requirements of being a leak-free seal. Also, an important strength of the syringe is its accuracy, which will help us deliver controlled and reproducible volumes of drops.

The products provided by Hamilton under the grant, will be used in the parabolic flight experiment, under gravity conditions (0g - 2g) to obtain new and original results.