Experimental data validates new theory for molecular diffusion in polymer matrices

After several years of developing theoretical ideas, researchers at the University of Illinois have been able to come up with multiple novel predictions about the fundamental mechanism of transport.

The theory was extended and tested against a large amount of data in a recent study. Chris Evans and a graduate student collaborated on the research.

A state-of-the-art theory was developed to predict how molecule move through complex media. The rate of transport is controlled by the features of the molecule and the medium that they are moving through.

Drug delivery, barrier coating, and self-healing are some of the applications of the diffusion of penetrants. It's difficult to control the rate of transport of penetrants through these matrices. The size of the molecule and the temperature can affect how fast a molecule moves through a material.

The team scoured the literature to find as much experimental data as possible. They were looking for data sets with the widest range of temperature to test their predictions, from high temperatures where polymers are rubbery, down to low temperatures where they end up in a glass. The new ideas of the theory were found in the 17 data sets analyzed.

Changing temperature can change diffusivity by 10 orders of magnitude. As temperature is lowered, the dispersion gets slower and slower, and in a more rapid manner that depends on the nature of the matrix.

It feels less resistance when the molecule is small and the temperature is high. When the molecule gets big enough, it must push more of the surrounding material out of the way to make it harder to move. The temperature dependence is completely changed by that, in a way that makes it easier to exploit the differences in the transport rate of different Molecules.

The rate of motion of a molecule can be affected by a number of factors, including temperature, penetrant size, and density. The result is a spectacular experiment.

A way to think about the synthesis of new molecule or new material with a tailored rate of temperature dependent transport is what comes out of this theory. It is similar to inverse engineering.

The study of the physical factors that control the transport of penetrants in glass-forming liquids has been published. 10.1073/pnas.2210019

Journal information: Proceedings of the National Academy of Sciences