Critical opalescence
Encyclopedia
Critical opalescence is a phenomenon which arises in the region of a continuous, or second-order, phase transition
. Originally reported by Thomas Andrews
in 1869 for the liquid-gas transition in carbon dioxide
, many other examples have been discovered since. The phenomenon is most commonly demonstrated in binary fluid mixtures, such as methanol
and cyclohexane
. As the critical point is approached the sizes of the gas and liquid region begin to fluctuate over increasingly large length scales. As the density fluctuations become of a size comparable to the wavelength of light, the light is scattered and causes the normally transparent fluid to appear cloudy. Tellingly, the opalescence
does not diminish as one gets closer to the critical point, where the largest fluctuations can reach even centimetre proportions, confirming the physical relevance of smaller fluctuations.
In 1908 the Polish physicist Marian Smoluchowski
became the first to ascribe the phenomenon of critical opalescence to large density fluctuations. In 1910 Albert Einstein
showed that the link between critical opalescence and Rayleigh scattering
is quantitativehttp://einstein-annalen.mpiwg-berlin.mpg.de/home.
More-detailed experimental demonstrations of critical opalescence may be found at
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
. Originally reported by Thomas Andrews
Thomas Andrews (scientist)
Thomas Andrews FRS was an Irish chemist and physicist who did important work on phase transitions between gases and liquids.-Life:Andrews was born in Belfast, Ireland where his father was a linen merchant...
in 1869 for the liquid-gas transition in carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, many other examples have been discovered since. The phenomenon is most commonly demonstrated in binary fluid mixtures, such as methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
and cyclohexane
Cyclohexane
Cyclohexane is a cycloalkane with the molecular formula C6H12. Cyclohexane is used as a nonpolar solvent for the chemical industry, and also as a raw material for the industrial production of adipic acid and caprolactam, both of which being intermediates used in the production of nylon...
. As the critical point is approached the sizes of the gas and liquid region begin to fluctuate over increasingly large length scales. As the density fluctuations become of a size comparable to the wavelength of light, the light is scattered and causes the normally transparent fluid to appear cloudy. Tellingly, the opalescence
Opalescence
Opalescence is a type of dichroism seen in highly dispersed systems with little opacity. The material appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opals.There are different degrees...
does not diminish as one gets closer to the critical point, where the largest fluctuations can reach even centimetre proportions, confirming the physical relevance of smaller fluctuations.
In 1908 the Polish physicist Marian Smoluchowski
Marian Smoluchowski
Marian Smoluchowski was an ethnic Polish scientist in the Austro-Hungarian Empire. He was a pioneer of statistical physics and an avid mountaineer.-Life:...
became the first to ascribe the phenomenon of critical opalescence to large density fluctuations. In 1910 Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
showed that the link between critical opalescence and Rayleigh scattering
Rayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...
is quantitativehttp://einstein-annalen.mpiwg-berlin.mpg.de/home.
External links
- A time-lapse video of critical opalescence in a binary mixture
- Account of Einstein's work on daylight and critical opalescence, with references
More-detailed experimental demonstrations of critical opalescence may be found at
- http://physicsofmatter.com/NotTheBook/CriticalOpal/Explanation.html
- http://www.msm.cam.ac.uk/doitpoms/tlplib/solid-solutions/demo.php