Solving the static charge dilemma for less clumpy shakes

Scientists from RMIT University and Riga Technical University in Latvia have shown that static charge left on surfaces can be controlled, which could help avoid the little zap in production of common household goods. The discovery also has potential in the food industry for helping to stop the clumping of powders such as protein, chocolate malt powders and coffee.

Most people have scooped out lumps from a protein shaker or chased a floating clump around a mug of chocolate milk, but few know that static electricity is one of the likely culprits. As powders rub and tumble during manufacturing, packing and pouring, the grains can pick up static charge and cling to each other.

The study, co-led by Dr Peter Sherrell, from RMIT’s School of Science, in collaboration with Riga Technical University, has shown that applying an electric field while two surfaces touch and pull apart controls how much static charge is left behind. It can also control whether that charge is positive or negative — or remove the charge.

These findings offer potential solutions to a range of food and electronics production challenges.

“For example, if we had a conveyor belt processing or sorting seeds, the static charge would change based on the size or species of the seed,” Sherrell said.

“Our discovery means we could change the electric field around the conveyor belt depending on the species, so there is no risk of a seed getting a static shock.”

The innovation could also help produce a smoother shake with less clumps.

“In principle, we could apply a small electric field across powders as they move,” Sherrell said.

“That stops them charging up, so they don’t get electrostatically ‘stuck’ to each other.”

The team tested plastics, rather than food products, but the findings of the study are a good indicator for how the team’s approach could apply to food powders.

The team plans to test the approach on real powders and to study programmable surfaces at much smaller scales, so that different parts of the same surface can be programmed in different ways.

Their current grant application with industry partners focuses on removing anti-static additives from fuels by tuning the surfaces the fuels touch, which could make fuel more energy-efficient.

Image credit: Will Wright, RMIT University.

Solving a longstanding puzzle

The research also offers evidence on a question scientists have debated for years: what makes charge separate when two materials touch and pull apart?

Computer simulations showed that the electric fields the team applied were similar in strength to those created naturally when rough plastic surfaces press together. This supports the idea that tiny built-in electric fields help drive the separation of charge in everyday static electricity.

How the research was done

In the video above, Dr Sherrell demonstrates that a polystyrene block and a thin layer of polystyrene attract each other after rubbing together and coming apart. When he ran an electric field through a material, this changed the static charge of the material. In the demonstration he shows an electrode attached to the polystyrene thin layer on a copper sheet. The effect is that the polystyrene block does not stick to polystyrene layer anymore.

The team pressed polystyrene films together and pulled them apart 500 times, while applying external electric fields.

Image credit: Will Wright, RMIT University.

Stronger fields left more charge, and reversing the field from positive to negative reversed the charge. The same behaviour appeared in all of the plastics tested.

These results were compared to the computational models to understand what was happening.

The scientists did the experiments in the lab on plastic films, mostly polystyrene, with other plastics in the supporting data. Food powders such as protein, malt drink additives and coffee were not tested.

The paper set the charge by applying a field during contact and then measured it afterwards. Switching the charge live, as in the conveyor example, hasn’t been demonstrated.

The simulations used a simplified model, and the approach hasn’t been tested on industrial equipment.

“The science would enable this to happen based on the discovery,” Sherrell said.

The research has been published in Nature Communications.

Top image credit: iStock.com/Gingagi