Novel Surfactants for Stabilizing Emulsions of Water or Hydrocarbon Oil-Based Droplets in a Fluorocarbon Oil Continuous Phase
Summary Emulsionsâ€”dispersions of two immiscible fluidsâ€”have many applications in industry and everyday life. These range from paints, to crop protection, chemical synthesis, and production of latices. They are also increasingly attractive for analytical applications. Traditional emulsions consist of water and hydrocarbon oil. However, this combination does not allow for a wide variety of applications. It is therefore of advantage to replace one of these liquids with a third class of liquids that are immiscible with water and hydrocarbon oils / organic solvents: the liquids of choice are fluorocarbon oils. The application of fluorocarbon oils as a continuous emulsion phase offers a number of advantages over the conventional water-in-oil (w/o) and oil-in-water (o/w) emulsions. For example, fluorocarbon oils provide an excellent barrier between individual emulsion droplets that consist of water, hydrocarbon oils or hydrocarbon solvents. Therefore, these droplets may be regarded as perfectly isolated entities, in which chemical or biological processes may occur independently. However, emulsions are inherently unstable. They have to be stabilized with appropriate surfactants to prevent the coalescence of droplets. So far there are no non-ionic fluorosurfactants available that would be suited for the stabilization of water-in-fluorocarbon (w/f) and oil-in-fluorocarbon (o/f)) emulsions. However, such surfactants are crucial for exciting new applications: 1) Water in fluorocarbon oil (w/f) emulsions Encapsulation of biological materials (DNA, proteins, cells) in aqueous droplets is interesting for high throughput screening. Using fluorocarbon oils as the continuous phase greatly reduces cross-contamination from one droplet to another, allows for efficient transport of oxygen to encapsulated cells, and ensures compatibility with the most common materials used to fabricate microfluidic devices (e.g. PDMS). Non-ionic surfactants are required to preserve the activity of biological materials by preventing their adsorption onto the droplet interface. 2) Organic in fluorocarbon oil (o/f) emulsions In many cases it is desirable to confine chemical reactions inside of droplets. However, in order to confine water-sensitive chemical reactions, a non-aqueous, inert, immiscible continuous phase must be used: fluorocarbon oils are a suitable alternative. Moreover, fluorocarbon oils allow for an exceptional transport of gases (H2, O2, CO2 etc.) for heterogeneous reactions due to their high solubility. Additionally, such reactions benefit from the great specific surface of the emulsion droplets. Other fields of application include high throughput analysis and templated synthesis. The same surfactants may also be used in processes involving supercritical CO2.
The technology presents a variety of novel non-ionic surfactants and surfactant systems for stabilizing aqueous or organic droplets in a fluorophilic continuous phase. Currently available fluorosurfactants have a number of serious drawbacks when applied towards performing biology in w/f or chemistry in o/f emulsions:
A) The commercial fluorosurfactants that are made for stabilizing droplets in fluorocarbon oils contain ionic headgroups. Therefore they are suitable for stabilizing aqueous drops only. However, ionic headgroups may interfere with biological compounds contained in the aqueous droplets. Surfactants for stabilizing droplets of hydrocarbon oils or organic solvents are not available with suitable geometry.
B) All commercial, non-ionic fluorosurfactants are designed for the stabilization of fluorocarbon-in-oil and fluorocarbon-in-water emulsions. These compounds generally contain relatively short fluorotelomers. Hence their geometry is not suited for the stabilization of aqueous or organic droplets in fluorocarbon oils. Moreover, these short fluorocarbon moieties limit the long-term steric stabilization of inverse (w/f and o/f) emulsions.
The surfactants provided here solve these problems. They make the stabilization of organic droplets in fluorocarbon oils as the continuous phase possible. Being non-ionic in nature, they also present an alternative to ionic surfactants for w/f emulsions.
â€¢ liquids and do not cause swelling or deformation of plastics and rubbers.
â€¢ This new class of surfactants provides long-term colloidal stabilization of hydrocarbon droplets in a fluorophilic continuous phase.
â€¢ These non-ionic fluorosurfactants allow for the stabilization of aqueous droplets in fluorocarbon oils without charging the inner droplet interface.
â€¢ These surfactants may be used for other applications involving supercritical CO2.
Fluorocarbon oils as a continuous emulsion phase have a number of other inherent advantages: they are inert, non-toxic, and not flammable; they have high gas permeability, low dielectric constant and refractive index; they are immiscible with common
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Weitz, David A.
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