Liquid crystal advance could boost food shelf life

A team from Texas A&M University have discovered a method to manoeuvre the disc-shaped molecules of liquid crystals into distinct and separate layers – which significantly enhances their properties as a sealant.

The layering process, known as a “smectic phase”, is common with rod-shaped crystal molecules but has never been recorded with their disc-shaped equivalents, said group leader Zhengdong Cheng, assistant professor of chemical engineering. The research appears in the Physical Review E journal.

"Before this, no discotic smectic phase was known to exist,"​ Cheng said. "For some time, people have been really puzzled as to why the discs don't form layers.”​

He added the technology could be applied across a range of material including food packaging.

“Integrating such a sealant into food packaging would translate into foods staying fresher for longer periods of time”,​ said Cheng.

Atypical behaviour​

Liquid crystals are a state of matter between a conventional liquid and a solid crystal. In the group's experiments, each disc, composed of millions of atoms, was a single layer of inorganic crystals with an identical thickness of 2.68 nm and a diameter around 2,000 nm.

The discs are created by exfoliating crystals of a compound of zirconium phosphate, which is a type of synthetic crystal manufactured to help remove nuclear waste. Cheng was able to verify the suspension was in a liquid crystal form by placing the disc suspension between two light polarizers. Then using X-ray technology, he observed how the discs eventually arranged themselves into a stable state – usually forming column-like structures - through a process called self-assembly.

However, in Cheng's experiment the discs behaved in an uncharacteristic manner, forming themselves into separate layers. This atypical behaviour occurred because of particular characteristics of the disc dimensions, said the researchers. Each disc had an identical thickness – in this case 2.68 nm – but varying diameters. A further vital factor is that the ratio between the thickness and diameter had to be sizeable. The team hypothesised that previous attempts to layer these discs had failed because the ratios were too small.