Tag Archives: nanoparticles

Christmas diamonds

If you enjoyed a holiday dinner lit by candles then you might be interested to know that the majority of the light from the candle does not come from the combustion of the candle wax in the flame, but from the unburnt soot glowing in the intense heat of the flame.  The combustion process generates the heat and the blue colour in the centre of the flame. However, due to the lack of sufficient oxygen, the combustion of the candle wax is incomplete  and this produces particles of unburnt carbon.  The unburnt carbon forms soot or graphite, but also more exotic structures of carbon atoms, such as nano-diamonds.  The average candle has been estimated to produce about 1.5 million nano-diamonds per seconds, or maybe 10 billion nano-diamonds per Christmas dinner! Unfortunately, they are too small to see otherwise they would add a lot of sparkles to festive occasions.

The picture is an infrared image of a 1cm diameter candle.  About 2cm of the candle height extends from the bottom of the picture and the visible flame is about 2cm high.

Source:

Helen Czerski, Storm in a Teacup: The Physics of Everyday Life, London: Penguin Random House, 2016.

 

Slow moving nanoparticles

Random track of a nanoparticle superimposed on its image generated in the microscope using a pin-hole and narrowband filter.

A couple of weeks ago I bragged about research from my group being included in a press release from the Royal Society [see post entitled ‘Press Release!‘ on November 15th, 2017].  I hate to be boring but it’s happened again.  Some research that we have been performing with the European Union’s Joint Research Centre in Ispra [see my post entitled ‘Toxic nanoparticles‘ on November 13th, 2013] has been published this morning by the Royal Society Open Science.

Our experimental measurements of the free motion of small nanoparticles in a fluid have shown that they move slower than expected.  At low concentrations, unexpectedly large groups of molecules in the form of nanoparticles up to 150-300nm in diameter behave more like an individual molecule than a particle.  Our experiments support predictions from computer simulations by other researchers, which suggest that at low concentrations the motion of small nanoparticles in a fluid might be dominated by van der Waals forces rather the thermal motion of the surrounding molecules.  At the nanoscale there is still much that we do not understand and so these findings will have potential implications for predicting nanoparticle transport, for instance in drug delivery [e.g., via the nasal passage to the central nervous system], and for understanding enhanced heat transfer in nanofluids, which is important in designing systems such as cooling for electronics, solar collectors and nuclear reactors.

Our article’s title is ‘Transition from fractional to classical Stokes-Einstein behaviour in simple fluids‘ which does not reveal much unless you are familiar with the behaviour of particles and molecules.  So, here’s a quick explanation: Robert Brown gave his name to the motion of particles suspended in a fluid after reporting the random motion or diffusion of pollen particles in water in 1828.  In 1906, Einstein postulated that the motion of a suspended particle is generated by the thermal motion of the surrounding fluid molecules.  While Stokes law relates the drag force on the particle to its size and fluid viscosity.  Hence, the Brownian motion of a particle can be described by the combined Stokes-Einstein relationship.  However, at the molecular scale, the motion of individual molecules in a fluid is dominated by van der Waals forces, which results in the size of the molecule being unimportant and the diffusion of the molecule being inversely proportional to a fractional power of the fluid viscosity; hence the term fractional Stokes-Einstein behaviour.  Nanoparticles that approach the size of large molecules are not visible in an optical microscope and so we have tracked them using a special technique based on imaging their shadow [see my post ‘Seeing the invisible‘ on October 29th, 2014].

Source:

Coglitore D, Edwardson SP, Macko P, Patterson EA, Whelan MP, Transition from fractional to classical Stokes-Einstein behaviour in simple fluids, Royal Society Open Science, 4:170507, 2017. doi:

More uncertainty about matter and energy

woodlandvalley

When I wrote about wave-particle duality and an electron possessing the characteristics of both matter and energy [see my post entitled ‘Electron uncertainty’ on July 27th, 2016], I dodged the issue of what are matter and energy.  As an engineer, I think of matter as being the solids, liquids and gases that are both manufactured and occur in nature.  We should probably add plasmas to this list, as they are created in an increasing number of engineering processes, including power generation using nuclear fission.  But maybe plasmas should be classified as energy, since they are clouds of unbounded charged particles, often electrons.   Matter is constructed from atoms and atoms from sub-atomic particles, such as electrons that can behave as particles or waves of energy.  So clearly, the boundary between matter and energy is blurred or fuzzy.  And, Einstein’s famous equation describes how energy and matter can be equated, i.e. energy is equal to mass times the speed of light squared.

Engineers tend to define energy as the capacity to do work, which is fine for manufactured or generated energy, but is inadequate when thinking about the energy of sub-atomic particles, which probably is why Feynman said we don’t really know what energy is.  Most of us think about energy as the stuff that comes down an electricity cable or that we get from eating a banana.  However, Evelyn Pielou points out in her book, The Nature of Energy, that energy in nature surrounds us all of the time, not just in the atmosphere or water flowing in rivers and oceans but locked into the structure of plants and rocks.

Matter and energy are human constructs and nature does not do rigid classifications, so perhaps we should think about a plant as a highly-organised localised zone of high density energy [see my post entitled ‘Fields of flowers‘ on July 8th, 2015].  We will always be uncertain about some things and as our ability to probe the world around us improves we will find that we are no longer certain about things we thought we understood.  For instance, research has shown that Bucky balls, which are spherical fullerene molecules containing sixty carbon atoms with a mass of 720 atomic mass units, and so seem to be quite substantial bits of matter, exhibit wave-particle duality in certain conditions.

We need to learn to accept uncertainty and appreciate the opportunities it presents to us rather than seek unattainable certainty.

Note: an atomic mass unit is also known as a Dalton and is equivalent to 1.66×10-27kg

Sources:

Pielou EC, The Energy of Nature, Chicago: The University of Chicago Press, 2001.

Arndt M, Nairz O, Vos-Andreae J, Keller C, van der Zouw G & Zeilinger A, Wave-particle duality of C60 molecules, Nature 401, 680-682 (14 October 1999).

 

Mass produced nuclear power plants?

A slightly weird picture of the rather unusual House of Porcelain in Tianjin, which is slowly turning black in the smog.

Porcelain House in Tianjin, which is slowly turning black in the smog.

In the pocket of my coat I have a peculiar souvenir of my recent visit to China. It’s a white face-mask with a little filter built-in to one side. It cost 2 Yuan, or about £0.2, and was given to me by a research student in Tianjin, who worked in my lab in Liverpool for a year. She bought it for me one Saturday when we were going out sightseeing in Tianjin because the air quality was so poor it caught on the back of your throat. The smog was so thick you could not see the tops of even modestly tall buildings.

This is a daily reality for millions of people in many of China’s cities. I reported in my blog entitled ‘Year of the Air: 2013’ [November 20th, 2013] about the number of deaths from pollution.  PM2.5 that’s particles with a diameter less than 2.5 microns are damaging to human health. While I was in Beijing the level of PM2.5 was 144 micrograms per cubic metre, compared to 13 at home in Liverpool.  My student’s mother had visited her while she was in Liverpool and I asked what she liked most during her visit – the fresh air was her reply.

I can’t really remember smog in England though I do remember buildings in the city centres being gradually cleaned because the smog had turned them black. And I remember shortly after I finished my PhD, being shown by a collaborator in the Pathology Department, the lungs from a recent post-mortem – they were grey-black from the smog!

The scale of the problem is difficult to grasp. Tianjin is a provincial city about 30 minutes by bullet train south-east of Beijing with a population of 14 million people, almost twice that of London, and 2.4 million cars.  The smog is generated by pollution from factories, power-stations and cars.  Hybrid cars could make a difference but there are none because they are too expensive, a Beijing colleague told me as he drove me in his brand new Volkswagen Passat. Plug-in cars would not solve the problem because the electricity would come mainly from coal-fired power stations, so the pollution would be simply moved elsewhere.

China needs clean energy, fast and lots of it.  In 2011 China’s installed electricity generating capacity was  about 1TW (Tera Watts or 1 with 12 noughts after it), of which about 2% comes from China’s 21 operating nuclear power plants.  Typical modern nuclear power plants take years to build and generate around 1,000 MW; perhaps we should be considering the small-scale mass production of medium-size modular power plants.  Huge, complex, reliable aeroplanes are made in this way, for instance the current Airbus A380 is production rate is about 25 per year.  So why not medium-size nuclear power plants?  Mass-production would also make decommissioning cheaper since it not be a bespoke process for each plant.

Maybe now that the Lockheed Martin’s Skunk Works have turned their attention to developing a fusion reactor, power-stations will be produced like airliners before I retire.

Sources:

Porcelain House, Tianjin

http://blogs.wsj.com/chinarealtime/2014/10/27/desperate-measures-as-world-leaders-visit-beijing-tries-to-reduce-pollution-by-40/

http://aqicn.org/city/united-kingdom/liverpool-speke/

BTW – My pathology colleague and I were interested in whether people with osteoporosis could break their hips and fall, rather than the usual assumption of falling and break their hips. See:

Wilkinson JM, Cotton DWK, Harris SC & Patterson EA, Assessment of osteoporosis at autopsy: mechanical methods compared to radiological and histological techniques, Medicine, Science & the Law, 31(1):19-24, 1991.

Cotton DWK, Whitehead CL, Vyas S, Cooper C & Patterson EA, Are hip fractures caused by falling and breaking or breaking and falling? Forensic Science Int., 65(2):105-112, 1994.