World Library  
Flag as Inappropriate
Email this Article

Ouzo effect

Article Id: WHEBN0015470144
Reproduction Date:

Title: Ouzo effect  
Author: World Heritage Encyclopedia
Language: English
Subject: Sambuca, Țuică, Soft matter, Liqueur, Condensed matter physics
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Ouzo effect

The ouzo effect during the preparation of absinthe.
Arak with water and ice

The ouzo effect (also louche effect and spontaneous emulsification) is a milky (louche) oil-in-water microemulsion that is formed when water is added to ouzo and other anise-flavored liqueurs and spirits, such as pastis, raki, arak, sambuca, absinthe and Pernod. Because such microemulsions occur with only minimal mixing and are highly stable,[1] the ouzo effect may have commercial applications.

Observation and explanation

Video of water being poured into a solution of 151-proof Everclear and essential oils from grapefruit rinds.

The ouzo effect occurs when a strongly hydrophobic essential oil such as trans-anethole is dissolved in a water-miscible solvent, such as ethanol, and the concentration of ethanol is lowered by addition of small amounts of water.

In water-immiscible solvents, oil-in-water emulsions are not stable as the oil droplets coalesce until complete phase separation is achieved at macroscopic levels. It is well known that the addition of a small amount of surfactant or the application of high shear rates (strong stirring) can stabilize the oil droplets.

In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid-liquid nucleation.[2] The size of the droplets has been measured by small-angle neutron scattering to be on the order of a micrometre.[3]

Using dynamic light scattering, Sitnikova et al.[1] showed that the droplets of oil in the emulsion grow by Ostwald ripening, and that droplets do not coalesce. The Ostwald ripening rate is observed to diminish with increasing ethanol concentrations until the droplets stabilize in size with an average diameter of 3micrometre.

Based on thermodynamic considerations of the multi-component mixture, the emulsion derives its stability from trapping between the binodal and spinodal curves in the phase diagram.[3] However, the microscopic mechanisms responsible for the observed slowing of Ostwald ripening rates at increasing ethanol concentrations appears not fully understood.

Applications

Microemulsions have many commercial uses. A large range of prepared food products, detergents, and body-care products take the form of emulsions that are required to be stable over a long period of time. The ouzo effect is seen as a potential mechanism for generating surfactant-free microemulsions without the need for high-shear stabilisation techniques that are costly in large-scale production processes. It has been conjectured[4] that the synthesis of a variety of dispersions such as pseudolatexes, silicone emulsions, and biodegradable polymeric nanocapsules, have been synthesized as a result of the ouzo effect.

See also

References

  1. ^ a b Sitnikova, Natalia L.; Rudolf Sprik, Gerard Wegdam and Erika Eiser (2005). "Spontaneously Formed trans-Anethol/Water/Alcohol Emulsions: Mechanism of Formation and Stability" (PDF). Langmuir 21 (16): 7083–7089.  
  2. ^ Vitale, Stephen A.; Joseph L. Katz (May 2003). "Liquid Droplet Dispersions Formed by Homogeneous Liquid-Liquid Nucleation: The Ouzo Effect". Langmuir (American Chemical Society) 19 (10): 4105–4110.  
  3. ^ a b Grillo, Isabelle (September 2003). "Small-angle neutron scattering study of a world-wide known emulsion: Le Pastis" (PDF). Colloids and Surfaces A, Physicochemical and Engineering Aspects 225 (1-3): 153–160.  
  4. ^ Ganachaud, François; Joseph L. Katz (2005). "Nanoparticles and Nanocapsules Created Using the Ouzo Effect: Spontaneous Emulsification as an Alternative to Ultrasonic and High-Shear Devices". ChemPhysChem 6 (2): 209–216.  

External links

Media related to at Wikimedia Commons

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.