Louche effect

from Wikipedia, the free encyclopedia
Louche effect through cooling with Ouzo

The louche effect ( French louche , 'opaque', 'suspicious', 'disreputable') is the milky cloudiness of clear aniseed spirits such as absinthe , pastis , sambuca , ouzo , mastika , rakı or arak when they are diluted with water or very strong be cooled. The aniseed content of different drinks can be compared with the help of the louche effect: the more cloudy the liquid becomes at a certain mixing ratio, the more aniseed there is in the distillate.

Basics

The cause of the louche effect is the content of essential oils , especially from the anise seeds and possibly from other aromatic plants such as mint , coriander and lemon balm . These oils, which contain a lot of anethole in aniseed schnapps , dissolve in alcohol , but not or only hardly in water . Rather, water as a hydrophilic (polar) substance and the ingredients of the hydrophobic essential oils form an oil-in-water emulsion in which hydrophobic oil particles are surrounded by water. The droplet diameter is around one micrometer . The light is scattered at the interfaces between water and oil droplets, which causes the milky-white turbidity. So it is not based on a chemical reaction, but is of a physical nature (see also Tyndall effect ).

The louche effect can also be created without adding water by strongly cooling aniseed schnapps. At low temperatures, the solvent power of alcohol decreases and oil droplets also form.

Ouzo effect

Although the Louche effect as such has been known for a long time, the term ouzo effect has been established in the scientific world since 2003 for the spontaneous formation of emulsions in a three-component system of immiscible and miscible liquids without the addition of energy or surface-active substances . These microemulsions form spontaneously and are extremely stable. The addition of the hydrophilic solution saturates the hydrophobic phase, which leads to the formation of small aggregates or droplets. The formation of such an emulsion is usually observed by means of dynamic light scattering . At first there is a homogeneous nucleation, which leads to a uniform dispersion. The aggregates or droplets grow to a diameter of a hundred nanometers to a few micrometers through Ostwald ripening and do not coalesce . The size distribution is very uniform ( monodisperse ). The final size cannot be influenced by the pH value , the ionic strength or by stirring, but depends solely on the ratio of the dissolved substance to the solvent. What limits growth is not yet fully understood. However, the entire process only takes place within a narrow concentration window. The metastable dispersions arise only between the spinodal and the binodal of the phase diagram of the respective mixture.

application

The louche effect is important for a large number of applications, as a wide variety of substances such as polymers , oils , fats or even drugs in aqueous solution can be easily emulsified by this effect. These emulsions have a high stability and are free from emulsifiers. Therefore, they are particularly interesting for the food industry , but also for the cosmetic or pharmaceutical industry. In addition, a wide range of particles in the sub-micrometer range can be produced for nanotechnology and biotechnology . By changing the concentration or combining different dissolved substances, nanocapsules or other nanoparticles can be synthesized in a simple manner.

Web links

Commons : Louche effect  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d Joachim Schüring: Why do aniseed schnapps turn milky and cloudy when you mix them with water? In: Spektrum.de. July 13, 2003, accessed November 25, 2013 .
  2. ↑ a b anethole, isoanethole. In: leaf spices. Heinrich-Heine-University Dusseldorf. Retrieved November 25, 2013 .
  3. ^ A b c d Robert Botet: The “ouzo effect”, recent developments and application to therapeutic drug carrying . In: Journal of Physics: Conference Series . tape 352 , March 5, 2012, ISSN  1742-6596 , p. 012047 , doi : 10.1088 / 1742-6596 / 352/1/012047 ( online ).
  4. ↑ a b Stephen A. Vitale, Joseph L. Katz: Liquid Droplet Dispersions Formed by Homogeneous Liquid-Liquid Nucleation: The Ouzo Effect . In: American Chemical Society (Ed.): Langmuir . 19, No. 10, May 2003, pp. 4105-4110. doi : 10.1021 / la026842o .
  5. ↑ Natalia L. Sitnikova, Rudolf Sprik, Gerard Wegdam and Erika Eiser: Spontaneously Formed trans-Anethol / Water / Alcohol Emulsions: Mechanism of Formation and Stability Archived from the original on October 23, 2013. (PDF) In: Langmuir . 21, No. 16, 2005, pp. 7083-7089. doi : 10.1021 / la046816l . PMID 16042427 . Retrieved November 30, 2013.
  6. ↑ Study Of “Ouzo Effect” May Lead To Design Of Improved Drugs, Cosmetics. In: ScienceDaily. February 20, 2008, accessed November 25, 2013 .