Painting by hedgehogs (Day 258)

Painting by hedgehogs (Day 258)

9th February 2015

For timid slow moving animals, hedgehogs and their relations are found all over Asia, Africa and Europe.

A few years ago they were the subject of a chemically-engineered joke when 'Hedgehog Flavoured Crisps' (potato chips) were sold in the UK.

Thankfully, no hedgehogs were hurt in their manufacture, but their taste (whatever that was) was mimicked using pork fat.

Now the hedgehog name has been used in the context of a new environmentally-friendly paint, and other applications.

University of Michigan researchers have developed a process that can sprout microscopic spikes on nearly any type of particle. They are called "hedgehog particles" due to their bushy appearance under the microscope.

The new process modifies oily, or hydrophobic, particles, enabling them to disperse easily in water. It can also modify water-soluble, or hydrophilic, particles, enabling them to dissolve in oil or other oily chemicals.

The unusual behavior of the hedgehog particles came as something of a surprise to the research team, including Nicholas Kotov, a professor of chemical engineering, biomedical engineering, materials science and engineering and macromolecular science and engineering.

Nicholas said: "We thought we'd made a mistake. We saw these particles that are supposed to hate water dispersing in it and we thought maybe the particles weren't hydrophobic, or maybe there was a chemical layer that was enabling them to disperse.

"But we double-checked everything and found that, in fact, these particles defy the conventional chemical wisdom that we all learned in high school."

The team found that the tiny spikes made the particles repel each other more and attract each other less. The spikes also dramatically reduce the particles' surface area, helping them to diffuse more easily.

One of the first applications for the particles is likely to be in paints and coatings, where toxic volatile organic compounds (VOCs) like toluene are used to dissolve pigment.

Pigments made from hedgehog particles could potentially be dissolved in nontoxic carriers like water.

This would result in fewer VOC emissions from paints and coatings, which the US Environmental Protection Agency estimates at over eight million tons per year in the United States alone.

VOCs can cause a variety of respiratory and other ailments and also contribute to smog and climate change. Reducing their use has become a priority for the Environmental Protection Agency and other regulatory bodies worldwide.

Nicholas says: "VOC solvents are toxic, they're flammable, they're expensive to handle and dispose of safely. So if you can avoid using them, there's a significant cost savings in addition to environmental benefits."

Another member of the team and chemical engineering doctoral student, Joong Hwan Bahng, said: "I think one thing that's really exciting about this is that we're able to make such a wide variety of hedgehog particles. It's very controllable and very versatile."

The researchers say the process is also easily scalable, enabling hedgehog particles to be created 'by the bucketful'.

Other potential applications include better oil dispersants that could aid in the cleanup of oil spills and better ways to deliver non-water-soluble prescription medications.

Another thorny environmental problem solved by chemical engineers. Well done to the team for this impressive piece of work.