Computational Chemistry

Computer giant IBM has used its computational nous to develop a new type of polymer that is stronger than bone, self healing and fully recyclable. Engineering Materials charts the progress of this breakthrough.

A team at computer giant IBM have used their knowhow when it comes to the digital world, to produce something very physical, a new type of polymer – the first in decades. The process they’ve used has been as pioneering – at least in application – as the material itself.

The breakthrough happened by combining the company’s high-performance computing knowledge with material engineering. IBM scientists used a novel ‘computational chemistry’ hybrid approach to accelerate the materials discovery process that couples lab experimentation with the use of high-performance computing to model new polymer-forming reactions.

The unconventional method is a departure from traditional techniques and led to the identification of several previously undiscovered classes of polymers in what was believed to be an established area of materials science and research.

“Although there has been significant work in high-performance materials, today’s engineered polymers still lack several fundamental attributes,” says James Hedrick, advanced organic materials scientist, IBM Research. “We're now able to predict how molecules will respond to chemical reactions and build new polymer structures, with significant guidance from computation that facilitates accelerated materials discovery.

“This is unique to IBM and allows us to address the complex needs of advanced materials for applications in transportation, microelectronic or advanced manufacturing.”

Ideally, scientists want to establish the method as a way to further develop advanced materials where they could insert a list of requirements into a computer, which would then design a material to meet exact criteria.

The reality, for now at least, is that materials are still primarily improved – and indeed discovered –though lab experimentation, physical testing and the knowledge, experience and educated guesses of the materials researcher.

IBM Research’s computational chemistry efforts, however, looks to lead to a different process that can take out a lot of guesswork and accelerate development across a new range of potential materials to meet the challenges of new and emerging applications.

For example, in the semiconductor industry this would bolster fabrication yields for chips, while saving money and significantly decreasing waste. In addition, the development of new polymers could deliver cheaper, lighter, stronger and recyclable materials ideal for aerospace and automotive applications.

Moreover, the ability to selectively recycle a structural component could have a major impact on advanced manufacturing, as companies would be able to rework high-value, but defective, parts--instead of throwing them away to landfills or junkyards.

The new polymer material the scientists have discovered here highlights the potential for further development of the computational chemistry process. It is stated the process is able to take a regular polymer and transform its structure to further bolster strength by 50% making them ultra strong and lightweight.

The material can also be manufactured to have even higher strength if carbon nanotubes or other reinforcing fillers are mixed into the polymer and are heated to high temperatures.

Limitations

Polymer materials have many limitations. Many are exposed to environmental factors (de-icing of aeroplanes, exposure to fuels, cleaning products) and exhibit poor environmental stress crack resistance (ie catastrophic failure upon exposure to a solvents).

Also, in many cases polymers are difficult to recycle as they cannot be remoulded or reworked once cured or thermally decompose upon heating to high temperatures. As a result, many end up in landfill together with toxins such as plasticisers, fillers, and colour additives that are not biodegradable.

IBM’s discovery is the ability to fine tune a range of desirable properties to provide an optimised material for a particular application. In addition, the ability to selectively recycle a structural component and rework high-value, but defective, parts would bolster fabrication yields.

Tuneable process

The polymers are formed through a condensation reaction where molecules join together and lose small molecules as byproducts such as water or alcohol. The process is said to be operationally simple but incredibly tuneable.

At high temperatures, around 250°C, the polymer becomes incredibly strong due to the rearrangement of covalent bonds and the loss of solvent trapped in the polymer. However, as with everything there is a trade off. Ductility suffers and the material becomes more brittle, and likely to shatter at failure in the same way as glass.

Another interesting attribute is that the polymer remains intact when it is exposed to basic water (high pH), but selectively decomposes when exposed to very acidic water (very low pH). It means, under the right conditions, the polymer will revert back to its original state enabling it to be reused the same as virgin polymer.

At low temperatures (just over room temperature), another type of polymer can be formed into elastic gels that are stronger than most polymers. It maintains its flexibility because of solvent that is trapped within the network, allowing it to stretch like rubber.

Self healing

Probably the most unexpected and remarkable characteristic of these gels is that, if they are severed and the pieces are placed back together and are physically touching, the chemical bonds are reformed between the pieces making the material a single unit again within seconds. Its ‘self healing’ property is made possible due to hydrogen bonding interactions in the hemiaminal polymer network.

Such materials might well be used as adhesives or be mixed in with other polymers to induce self-healing properties in the polymer mixture. Furthermore, the new polymers are reversible constructs, which means that can be recycled in neutral water, so they might well find use in applications that require reversible assemblies, such as drug cargo delivery.

Author
Justin Cunningham

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