World Library  
Flag as Inappropriate
Email this Article

Pickering emulsion

Article Id: WHEBN0015875167
Reproduction Date:

Title: Pickering emulsion  
Author: World Heritage Encyclopedia
Language: English
Subject: Janus particles, Emulsion, Soft matter, Dosage forms, Condensed matter physics
Collection: Chemical Mixtures, Condensed Matter Physics, Dosage Forms, Drug Delivery Devices, Soft Matter
Publisher: World Heritage Encyclopedia

Pickering emulsion

A Pickering emulsion is an emulsion that is stabilized by solid particles (for example colloidal silica) which adsorb onto the interface between the two phases. This type of emulsion was named after S.U. Pickering, who described the phenomenon in 1907, although the effect was first recognized by Walter Ramsden in 1903.[1][2]

If oil and water are mixed and small oil droplets are formed and dispersed throughout the water, eventually the droplets will coalesce to decrease the amount of energy in the system. However, if solid particles are added to the mixture, they will bind to the surface of the interface and prevent the droplets from coalescing, thus causing the emulsion to be more stable.

Properties such as hydrophobicity, shape, and size of the particle can have an effect on the stability of the emulsion. The particle’s contact angle to the surface of the droplet is a characteristic of the hydrophobicity. If the contact angle of the particle to the interface is low, the particle will be mostly wetted by the droplet and therefore will not be likely to prevent coalescence of the droplets. Particles that are partially hydrophobic (i.e. contact angle of approximately 90°) are better stabilizers because they are partially wettable by both liquids and therefore bind better to the surface of the droplets. The stabilization energy is given by

\Delta E\ = \pi r^2\gamma_{OW}(1-|cos{\theta_{OW}}|)^2

where r is the particle radius, \gamma_{OW} is the interfacial tension, and \theta_{OW} is the contact angle. When the contact angle is approximately 90°, the energy required to stabilize the system is at its minimum.[3] Generally, the phase that preferentially wets the particle will be the continuous phase in the emulsion system.

Additionally, it has been demonstrated that the stability of the Pickering emulsions can be improved by the use of amphiphilic "Janus particles", due to the higher adsorption energy of the particles at the liquid-liquid interface.[4] This is evident when observing emulsion stabilization using polyelectrolytes.

Homogenised milk is an example of a Pickering-stabilized emulsion. Casein (protein) units are adsorbed at the surface of milk fat globules and act as a surfactant. The casein replaces the milkfat globule membrane, which is damaged during homogenisation.

Recently, using latex particles for Pickering stabilization and then fusing these particles to form a permeable shell, a new form of capsule, called a colloidosome, has been developed. According to the definition of Dinsmore, a colloidosome is a selectively permeable capsule that is composed of colloidal particles.[5] Moreover, Pickering emulsion droplets are suitable templates for micro-encapsulation and the formation of closed/non-permeable capsules as well.[6]

Recently, it was shown that dispersions consisting of phase-separated aqueous polymer solutions can be stabilised using Pickering stabilisation.[7]

See also


  1. ^ S.U. Pickering, J. Chem. Soc. 91 (1907) 2001
  2. ^ W. Ramsden, Proc. R. Soc. London 72 (1903) 156
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^
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, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for 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 Project Gutenberg 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.