Electric fields can program static charge, pointing to less clumpy protein shakes

Researchers in Australia and Latvia report that the static charge left behind when two surfaces touch and pull apart can be deliberately controlled, switched and even erased by applying an external electric field at the moment of contact. The study, published in Nature Communications, was co-led by Dr Peter Sherrell of RMIT University's School of Science in collaboration with Riga Technical University, and its findings suggest that surfaces could be engineered with static charge formation programmed to suit specific applications. Instead of suppressing static with expensive conductive additives, a one-size-fits-all fix that industry often relies on, the researchers propose surfaces whose static behaviour can be tuned to the application.

Potential uses include anti-static surfaces for manufacturing and electronics processing, controlling where charged particles or plastics stick and how they assemble, smarter sensors, and smart air and gas filters. The discovery could also one day help stop powders such as protein powder, chocolate malt powders and coffee from clumping, a problem in which static electricity is one of the likely culprits. The experiment was straightforward in concept.

The team pressed polystyrene films together and pulled them apart 500 times, applying external electric fields while the surfaces were in contact. The results were systematic. Stronger fields left more charge on the separated surfaces.

Reversing the field from positive to negative reversed the polarity of the charge left behind. The same behaviour appeared in all of the plastics tested, indicating that the effect is not specific to a single polymer but a general property of how charge separates during contact, friction and separation. The study also offers evidence on a question scientists have debated for years: what makes charge separate when two materials touch and pull apart?

Computer simulations run by the team showed that the electric fields applied in the laboratory were similar in strength to those created naturally when rough plastic surfaces press together. This agreement supports the idea that tiny built-in electric fields, arising at the microscopic points where rough surfaces meet, help drive the separation of charge in everyday static electricity. In other words, the fields the researchers applied externally appear to act on the same mechanism that produces static naturally.

Dr Andris Šutka of Riga Technical University is the first author and co-corresponding author of the paper, and Professor Amanda Ellis of the University of Melbourne is a co-author. PhD student Dumindu Dassanayaka and Dr Qiang Sun from RMIT are also key contributors. According to the researchers, the discovery means static charge is no longer a fixed outcome determined only by whichever materials happen to rub together; the field applied during contact can set how much charge remains, which sign it carries, or whether any charge remains at all.

One of the most relatable potential applications is the protein shake. Many people have chipped lumps out of a shaker bottle or chased a floating clump around a mug of chocolate milk, and few realise 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, forming the clumps that make mixing frustrating.

In principle, Sherrell explains, a small electric field could be applied across powders as they move through production. That stops them charging up, so they do not become electrostatically stuck to each other. The team has not yet tested food powders.

The laboratory experiments used plastics rather than protein, chocolate malt additives or coffee, although the researchers note that the findings are a good indicator of how the approach could apply to food powders. The next step, Sherrell says, is to find out how strong the field needs to be, how long to apply it for each powder, and where in the process it works best. 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.

The applications extend beyond powders. In an example Sherrell offers, a conveyor belt processing or sorting seeds would generate static charge that changes based on the size or species of the seed. With the new discovery, the electric field around the conveyor belt could be changed depending on the species, so there is no risk of a seed getting a static shock.

The team's current grant application with industry partners focuses on a different target: removing anti-static additives from fuels by tuning the surfaces the fuels touch, which could make fuel more energy efficient. The scale of the potential benefit is considerable. Industry currently adds expensive conductive additives as a general fix to reduce static, and the cost of static discharge is about US$5 billion in the electronics industry alone.

A programmable alternative, in which surfaces are engineered to carry whatever charge behaviour a process requires, could in principle replace some of those additives and give manufacturers a controllable parameter rather than a hazard to avoid. Sherrell says the science would enable this to happen based on the discovery, while noting that the engineering has yet to be developed. The limitations of the study are clearly acknowledged.

The experiments were performed in the laboratory on plastic films, mostly polystyrene, with other plastics appearing 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, so switching the charge live, as in the conveyor belt example, has not been demonstrated.

The simulations use a simplified model, and the approach has not been tested on industrial equipment. These boundaries separate a controlled laboratory result from a production-line technology, and the researchers are explicit that the work so far establishes the enabling science rather than a finished solution. Even within those boundaries, the study carries weight for what it says about a phenomenon that has resisted tidy explanation.

The agreement between the applied fields and the naturally arising fields at rough surface contacts suggests the team may have identified a mechanism behind contact electrification and found a way to control it. The research was supported by the Latvian Central Finance and Contracting Agency through the ERC project TriboCharge and by an RMIT Vice-Chancellor's Research Fellowship. If follow-up work on real powders and finer-scale programmable surfaces succeeds, the invisible fields that make powders stick and electronics fail could become a controllable part of manufacturing, and the clumps in a protein shake may one day be a solved problem rather than a daily annoyance.

Subject of Research: Programmable control of static charge during contact, friction and separation of polymer surfaces

Article Title: ‘Invisible’ tweak could help make protein shakes less clumpy

Article References: ‘Invisible’ tweak could help make protein shakes less clumpy. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: static electricity, triboelectric effect, contact electrification, electric fields, polymers, polystyrene, powders, protein shakes, anti-static surfaces, RMIT University, Riga Technical University, Nature Communications