Feb 16 2015
Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have conducted a new study on how various non-spherical particles could be created by releasing molten wax droplets into a bath of cooler liquid.
The four resulting shapes generated by the research were made by variations in factors such as the speed of impact, temperature of the fluids, and the density of the liquid bath the particles were dropped in. Credit: OIST
This new study shows that different types of non-spherical shapes can be created and reproduced with many industrial applications. The study was performed at OIST’s Micro/Bio/Nanofluidics Unit. Amy Shen, an OIST Professor collaborated with Shilpa Beesabathuni from University of Washington, who was her former Ph.D student.
In industry, particles which have non-spherical shapes can be used for a wide range of potential uses. Non-spherical particles have special properties such as high packing densities, large surface areas and unique responses when subjected to external magnetic and electric fields. These properties make them favorable for various applications including drug delivery systems, absorbents, cosmetics and food processing.
Previous studies required specialised equipment for creating non-spherical particles that ranged in length from micron to millimeters. The production methods involved had limited scope. Prof. Shen's unit has developed a method that is simple, scalable and cost-effective and which could be applied to different kinds of liquids.
A single non-spherical particle can be created using this method and its shape would depend on the different variables that act in combination at the moment that the impact occurs. Molten liquid drops are formed and then released into a cool liquid bath for solidification in this method.
At the initial stages of this study, the physics that came into play during the creation of various particle shapes involving impact and solidification between wax and the cooler liquid medium was not clearly understood.
Wax was used as the molten liquid in this experiment. The researchers has to consider different variables, which included the temperature, viscosity and density of the liquid bath, the temperature of the wax and the speed of impact of the molten liquid drop.
The researchers balanced these variables with different time scales. They found that throughout the experiment, four shapes occurred. They were of ellipsoid, disc, flake-like and mushroom shapes.
In order to determine the time taken by a single molten wax drop to solidify after it made contact with the bath of cooler liquid, the team used high speed image analysis and a simple heat transfer model.
The data derived from this study enables reliable reproduction of these four non-spherical shapes. This also lays the foundation for creation of other particle types using comparable methods.
Professor Shen explains "People have done studies similar to this in the past using liquid metals impacting solid surfaces, but not other liquids. In terms of the fundamental physics, I believe this research is unique. In terms of applications it's also very important because of how simple and low cost this method is as well as how easily it can be scaled."
High speed drop imaging 高速滴下イメージング
Wax based particles have low melting points and could be used for application in cosmetics. However, Professor Shen states that the same types of methods would possibly work with polymeric and hydrogel materials that are sensitive to temperature.
In pharmaceutical applications, capsules are usually produced using these substances. This production method would enable new methods to create non-spherical capsules for delivery of drugs.
This study has been published in Journal of Colloid and Interface Science.