A Surprisingly Elegant Formula For Molecular Aggregates

A mathematical formula can describe the physical processes underlying whether milk turns into butter or curd, scientists say.

AsianScientist (Aug. 17, 2015) – Researchers have worked out a mathematical relationship between attractive and repulsive forces that determines the formation of two dimensional aggregate structures. Their research, published in Soft Matter, allow scientists to predict the emergence of bulk properties from the molecular level.

Churning raw milk sufficiently creates butter while adding lemon juice coagulates it into curd. Although these two phenomena are commonplace, they are not as straightforward as they sound on the molecular level.

When milk is churned, the fat molecules in it come closer to form aggregates. Lemon juice increases milk’s acidity and creates similar molecular lumps. Yet butter and curd are not solids because in both cases, the aggregated molecules still maintain consistent distances from each other, behaving as if they are part of a liquid.

There are similar liquids—both natural and man-made—where molecules pack together like a solid in certain localized regions of the bulk material. Gels and shaving cream are industrially crafted examples. Recipes for creating such materials exist, but scientists do not always understand why they work. Creating new types of functional materials from existing ones, therefore, depends on educated guesses and involves trial and error.

Joint research by the Okinawa Institute of Science and Technology Graduate University (OIST) and the Los Alamos National Laboratory has discovered a way to predict the emerging structures and bulk properties of molecular aggregations. Their discovery has significant technological implications in manufacturing new functional materials.

“What we found was a simple ratio that weighs the overall attractive forces against the overall repulsive forces in a material. Its value, under different experimental conditions, corresponds with the degree of molecular aggregation. From the existing mathematical tangles, the simplicity that emerged surprised us,” said Dr. Tamoghna Das, the paper’s lead author and a postdoctoral researcher in the OIST Collective Interactions Unit.

In real life bulk systems, it is the degree of molecular aggregation that defines the resulting material’s eventual properties. The OIST researchers ran 2D simulations involving tens of thousands of particles. To govern the simulated particles, they fed existing equations of intermolecular crowd control into their system and plugged in values that would lead to the formation of aggregates.

They tinkered with their numbers so that aggregation occurred in differing degrees. Variables like external temperature and overall density of distribution of the resulting aggregates were kept constant for each set of values. While searching for a relationship between the changing values of the parameters controlling their simulation and the changing degrees of aggregation, they discovered the mathematical relationship between short-range attraction and long-range repulsion. Their findings can easily be adapted to three dimensions, in accord with real life situations.

The discovery will allow experimentalists to bypass mathematical details of reorganizations occurring at the molecular level in these special materials. It will allow them to predict their emergent bulk properties using the minimum possible information, about external conditions manipulable via experiment.

The article can be found at: Das et al. (2015) A Minimal Description of Morphological Hierarchy in Two-Dimensional Aggregates.

———

Source: Okinawa Institute of Science and Technology.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Asian Scientist Magazine is an award-winning science and technology magazine that highlights R&D news stories from Asia to a global audience. The magazine is published by Singapore-headquartered Wildtype Media Group.

Related Stories from Asian Scientist