It seems that a suspension of
elemental carbon will work just as well while suffering the same difficulties
in handling and manufacture. So while we
are unlikely to find industrial microdiamonds in our laundry, it is likely high
time we reprised work that I was involved in twenty years ago with suspensions
of elemental carbon.
One commonly discussed topic in
this blog happens to be biochar in which the powerful crystalline acidic nature
of elemental carbon is applied.
This is yet another appearance of
the same results in a different setting.
The real problem is to separate a five nm fraction in the first
instance. In the meantime we discover
that a lighter oil can be used to suspend the particle seed which then steps
aside to allow the seed to interact with the denser oil. This explains why it was efficious in
creating nm sized bubbles of hyaluronic acid which is a large molecule to begin
with.
Neat stuff just waiting for us to
perfect manufacturing technology.
Nanodiamond laundry detergent can make your clothes sparkle
By Brian
Dodson
17:58 July 1, 2012
###
Diamonds in your washing machine can make your clothes sparkle (Photo:Shutterstock)
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.
### 2
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.
### 6
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
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.
### 1
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
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 40 year anniversary. What he didn't expect was that along the way he would become a patent agent, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.
Brian,
ReplyDeleteYou said 5 nm diamonds are fairly cheap.
I wonder if you could give a few links to sites selling these diamonds relatively inexpensively?
Thanks.
David