Shopping? Check out our latest product comparisons

Nanodiamond laundry detergent can make your clothes sparkle

By

July 1, 2012

Diamonds in your washing machine can make your clothes sparkle (Photo: Shutterstock)

Diamonds in your washing machine can make your clothes sparkle (Photo: Shutterstock)

Image Gallery (4 images)

We all do laundry, or are perhaps lucky enough to have someone who does laundry for us. Most of that wash is done in warm or hot water, because, regardless of the claims made for laundry detergents, most detergents don't work very well in cold water. Unfortunately, the wash water has to be heated, and given an average wash temperature of about 40°C (104°F), this uses around 5-10 kWh per load. If both the temperature of the water and the amount of water used in clothes washing could be cut in half, nearly a trillion kilowatt-hours of energy could be saved each year - 0.5% of the world's total energy use. All that is stopping us is finding better laundry detergents. That's where the diamonds come in.

The chemical engineering challenge presented by a load of wash is considerable. An average load of laundry contains 40-120 grams (1.4-4.2 oz) of dirt. This dirt is a witch's brew of proteins, carbs, starches, hydrocarbons, fats, minerals, clay, and other schmutz, mashed between and within the fibers of the various fabrics. Nearly all of this material is hydrophobic, that is, it actively repels water because it has lower surface energy than does water. (An alternate term is lipophilic, as the dirt is oil-like and is attracted to more oil.) So how do we get this hydrophobic dirt suspended in the wash water so it can be removed by draining and rinsing? This is the task of the laundry detergent.

Chemical structure of soap - the left end has the structure of an oil, while the right end...

Chemical structure of soap - the left end has the structure of an oil, while the right end has a structure that is attracted to water (Image: Smokefoot)

A basic detergent is also known as a surfactant. A surfactant is typically an organic molecule that has two separated chemical groups, one of which is hydrophilic, and the other of which is hydrophobic. In the figure above appears the oldest known surfactant - a simple soap. The soap molecule is essentially a linear hydrocarbon with a sodium salt at one end.

Schematic structure of a micelle. The hydrophilic end of the surfactant molecules rest in ...

Schematic structure of a micelle. The hydrophilic end of the surfactant molecules rest in contact with the aqueous solution surrounding the micelle, while the hydrophobic (or lipophilic) chains remain in the oil droplet enclosed by the micelle (Image: Emmanuel Boutet via Wikimedia)

When a surfactant is put in water and mechanically mixed with oil, the oil is taken up in micelles, as shown in the figure above. The surface of the micelles are happy in contact with water, so the oil can be separated into tiny droplets (perhaps 10-20 nm in size). Moreover, these micelles do not allow the oil to conglomerate into larger droplets, so that the oil remains suspended in the water. Removing the wash water and rinsing the laundry then removes most of the dirt.

A real laundry detergent includes more sophisticated surfactants than soap, usually so that they work better in hard water. In addition, laundry detergents are usually about 50 percent water softeners, chemicals added to remove calcium ions from the wash water. They may also include bleach, enzymes (to help degrade caked dirt so it can be solubilized), foaming agents, dye transfer inhibitors, fragrance, and many other additives.

Detergents do a remarkably good job with a very complex chemical process. However, most conventional detergents do not work well in cold water. The most difficult ingredients of the dirt to solubilize with detergents are crystallized fat and other lipid molecules - not too surprising, as we know grease sticks well to grease. Professor Andrew Marsh and his team at the University of Warwick decided to take on this problem.

They came up with the apparently crazy idea to add diamonds to laundry detergent to improve its cold washing ability. But let's dig down to discover why this approach isn't as silly as it might seem at first glance.

First, a key step in diamond mining as well as manufacture of synthetic diamond is to separate diamonds from the gangue (waste material) by passing the diamond-containing material over a grease table. The surfaces of a diamond are highly hydrophobic, so the diamonds stick to the grease. This is why jewelry stores have ultrasonic cleaners, to gently scrub away at the greasy surface of a diamond. So the notion that including diamonds in the laundry process might change how the crystallized fat reacts to the presence of the detergent has some rationale.

Second, industrial diamonds are not nearly as expensive as you might think. A gem-quality one-carat diamond (weighing 0.2 grams/0.007 oz) can easily cost US$10,000. In contrast, industrial diamond grit in large quantities can cost as little as four or five cents per carat, or about $200 per kilogram (2.2 lb). The concentration settled upon by March's team was 0.1 g/liter (0.003 oz/0.26 gal US) of washing water (about 0.0025 percent by volume), which would only add a US dollar or so to an average load of laundry.

Five nanometer diamonds as viewed by a scanning electron microscope (Photo: University of ...

Five nanometer diamonds as viewed by a scanning electron microscope (Photo: University of Warwick)

Third, one might suspect that such a small amount of diamond could not have any noticeable effect on the washing process. This is one reason that Marsh's team studied the effect of adding five nanometer nanodiamonds. At 0.1 g/l, the average distance between individual nanodiamond crystallites is about 200 nm. When one considers that the nanodiamonds will largely concentrate near the worst dirt in the clothing, you can imagine that the surface regions of crystallized fat will be well covered by nanodiamonds.

But wait - there's an obvious problem here. As the nanodiamonds are hydrophobic, how can they be well dispersed in the water-based washing liquid? They should agglomerate into larger clusters of nanodiamonds, and eventually settle out of the liquid, or at the very least become too sparse to affect the washing process. This concern is valid, and is avoided by initially forming a colloid which places surfactant molecules on the surfaces of the nanodiamonds. The surfactant molecules self-assemble so that their hydrophobic groups are attached to the nanodiamond surfaces, and their hydrophilic groups are exposed to the surrounding water. The result is that the nanodiamonds retain their individual identities and remain in suspension in the water.

It is perhaps surprising that doing the laundry is this complicated, but we're reaching the good part. The way to imagine the surfactant-coated nanodiamonds attacking the crystallized wax is as a fleet of very small Pac-Man eaters. Their mouths stay shut until they hit the wax surface, at which time the surfactant molecules move aside, allowing the nanodiamond to make contact with the wax. Now the nanodiamond acts as a handle on the wax crystallite to which it is attached, so that fluid motion and collisions act to break the wax crystallite to float away with the nanodiamond. Once the wax and nanodiamond are surrounded by water, it is energetically favorable for the nanodiamond to separate from the wax crystallite, after which the wax is coated with the detergents also present in the wash liquid, and the surfactant-coated nanodiamond is regenerated for further demolition of wax deposits.

The result? The amount of fat removed during a given washing test using the detergent with nanodiamonds was double that when using the detergent alone. At this point it isn't clear that we will soon be buying laundry detergent containing nanodiamonds. However, Marsh's research may prove a starting point for a more practical improvement. In any case, it is stimulating to encounter a research project so effective at rubbing one's nose in the extraordinary complexity of ordinary activities.

Source: University of Warwick

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
17 Comments

Thanks for this, now we'll be haunted by awful 'diamond finish' laundry detergent ads until this is actually a reality :P

Jelle Ursem
1st July, 2012 @ 10:34 pm PDT

Is this a problem in other countries? I grew up in New Zealand and live in Japan. I have never seen a hot-wash in either country.

jonoxn
2nd July, 2012 @ 01:53 am PDT

It's all very well improving detergents to work at lower and lower temperatures to reduce energy costs, but do these lower temperatures really clean clothes/bedding properly.

What I am referring to is things like dust mites and the multitude of other minuscule creepy crawlies that infest all of our clothes/bedding in their millions. Unless I'm mistaken, no detergent that is safe to use will kill these, only washing at 50C or above will do this. Let's not forget that 60% of asthma sufferers are allergic to dust mites and that there appears to be some correlation between an increase in asthma sufferers and the lowering of washing temperatures.

ChrisGn
2nd July, 2012 @ 04:47 am PDT

Chris, dryers operate at temperatures higher than 50 degree C.

NK Fro
2nd July, 2012 @ 07:10 am PDT

A the risk of sounding sexist, now diamonds really are a girls best friend. ;-)

Matt Taylor
2nd July, 2012 @ 07:41 am PDT

So, if the nano-diamonds break away from the wax crystals after liberating them from the fabric, do the nan-diamonds simply disappear down the drain or can they, in some fashion, be re-used?

Mirmillion
2nd July, 2012 @ 08:58 am PDT

What percentage of the diamonds remain in the clothes?

What is the impact, if any, "down the line"? (e.g., in sewage treatment plants and afterwards)

sieler
2nd July, 2012 @ 10:16 am PDT

Mirmillion, not only can they be reused but what are they doing in the water supply? I think there is some serious discussion about all the nanoparticles going into the environment from any number of sources. As gung-ho as I am about nanotechnology and its possibilities, I think this question ought to be answered, and soon.

SilverBee
2nd July, 2012 @ 10:22 am PDT

It goes down the drain.

What kind of surfactant molecule is used to attach to the diamond to form the colloids? I get that they're charge-stabilized.

Fretting Freddy the Ferret pressing the Fret
2nd July, 2012 @ 11:39 am PDT

Perhaps, then, a large nanodiamond filter could help in the capture of oil that has leaked out into the sea.

Sergius
2nd July, 2012 @ 11:57 am PDT

Watched an episode of 1000 ways to die where a guy was snorting cocaine and dealing in diamonds. The diamond dust got mixed into the cocaine and cut his lungs to pieces. I don't think I'll be doing any diamond laundry soon.

bugnuker
2nd July, 2012 @ 12:01 pm PDT

Wow. only a dollar more per load. i paid $8.00 for a detergent that does 81 loads. so, with diamonds it would only cost $8.00 plus another $81.00 for the diamonds. i can't wait to pay $89.00 for a jug of laundry detergent.

kar
2nd July, 2012 @ 12:04 pm PDT

So, knowing that diamonds are pretty abrasive, really small or not what affect is this going to have on the moving parts and seals of a washing machine or left overs that end up in the drier? Can we look forwards to washers and driers that last half as long?

John Kerher
2nd July, 2012 @ 12:40 pm PDT

5-10kWh for a load of washing at 40'C. Bunkum!

Say 20l = 20,000g of water starting at 20'C. That's a delta T of 20'C, x 1 cal/g = 400,000 calories (the physics kind, not the food kind. Wolfram Alpha will tell you that's less than HALF a kWh.

Or just use a common sense estimate: My electric kettle takes say 5 minutes to boil 1l of water (dT of 80'C, say). I've never timed it, but that's a reasonable first guess. If it's a 2kW element that's:

2kW * 5min/60min = 2/6 kWh for 1 litre * 80'C

for 20l / 80'C that would be 40/6 kWh

for 20l / 20'C that would be 10/6 kWh.

That's still closer to 1kWh than "5 to 10kWh".

More energy would be saved if people would not persist in boiling a full kettle just to make one cup of tea!

A 3rd common sense test: A average power outlet in Australia can deliver 2400W. 5 to 10kWh means it would take my washing machine 2-5 hours to heat the water.

splatman
2nd July, 2012 @ 01:11 pm PDT

"ONLY" a dollar or two extra per load? Neat science, but my soap only costs a few cents per load and the hot water not much more.....commercially viable? I think not.

Bryan Paschke
2nd July, 2012 @ 01:31 pm PDT

So hot water sets stains so there might be other benefits to cold water detergents. That said. if you cut the amount of water by 1/10th then you are really saving energy. Isn't that kinda the point of steam washers?? Kinda seems silly to waste time on the detergents when its the machines that make the difference.

Michael Mantion
2nd July, 2012 @ 04:22 pm PDT

And dryers use a lot more energy than you've saved by reducing the temperature!!! Besides, not everyone has a dryer!

ChrisGn
3rd July, 2012 @ 04:15 am PDT
Post a Comment

Login with your gizmag account:

Or Login with Facebook:


Related Articles
Looking for something? Search our 28,145 articles