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An emulsion is a mixture of two liquids that are typically immiscible (don't blend) that forms a two phase system. One of the two liquids is dispersed in the mixture, forming the dispersed phase. The other liquid contains the dispersion and is known as the continuous phase. An example of two immiscible liquids would be water and oil. In general an emulsion will be unstable since the dispersed phase will try to decrease it's surface tension by grouping with other dispersed droplets until the liquids separate again. However, a stable emulsion can be formed by the addition of emulsifiers, such as surfactants that distribute themselves around the interface between the two liquids, creating a stable system. Emulsions are generally regarded as a special class of colloids where both the continuous and dispersed mediums are liquid. However, this distinction is not rigid with some people such as Witten specifying the term colloid only for a mixture of solids and liquids.

A. Two immiscible liquids. B. An unstable emulsion with both a dispersed and continuous phase. C. The unstable emulsion slowly separates. D. An emulsion with a surfactant to stabilize the mixed system.

Soft Matter Examples

Emulsions are an important type of "soft matter". As a system, it has many properties of a liquid but depending on the size of the dispersed phase droplets, the properties of the emulsion will be very different than those of either pure liquid.

Examples of emulsions from everyday life include butter and margarine.

Emulsions are useful is aiding to form other types of dispersions. For example, in the paper Evaporation-Driven Assembly of Colloidal Particles, the author describes how emulsions of water and toluene can be used to assemble polystyrene particles into clusters of definite and unique structure.

It is possible to create PEG vesicles via a dewetting transition from a "W/O/W double emulsion" as discussed in Microfluidic Fabrication of Monodisperse Biocompatible and Biodegradable Polymersomes with Controlled Permeability.


[1] R. Jones, "Soft Condensed Matter," Oxford University Press Inc., New York (2002).

[2] Wikipedia "Emulsion"

[3] T. Witten, "Structured Fluids: Polymers, Colloids, Surfactants," Oxford University Press Inc., New York (2004).

Keyword in references:

All-aqueous core-shell droplets produced in a microfluidic device

Amphiphilic Crescent-Moon-Shaped Microparticles Formed by Selective Adsorption of Colloids

Contact angle associated with thin liquid films in emulsions

Double-emulsion drops with ultra-thin shells for capsule templates

High-throughput injection with microfluidics using picoinjectors

One-Step Emulsification of Multiple Concentric Shells with Capillary Microfluidic Devices

Patterned Colloidal Coating Using Adhesive Emulsions

Reversible aggregation of responsive polymer-stabilized colloids and the pH-dependent formation of porous scaffolds

Patterning Hierarchy in Direct and Inverse Opal Crystals

Liquid-infused structured surfaces with exceptional anti-biofouling performance

Electric-field-induced capillary attraction between like-charged particles at liquid interfaces

Evaporation-Driven Assembly of Colloidal Particles

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

Yielding and Flow of Monodisperse Emulsions

Swollen Vesicles and Multiple Emulsions from Block Copolymers

Spontaneous Formation of Lipid Structures at Oil/Water/Lipid Interfaces

Production of Unilamellar Vesicles Using an Inverted Emulsion

Short-time self-diffusion of nearly hard spheres at an oil–water interface

Hierarchical Porous Materials Made by Drying Complex Suspensions

Double Emulsion Droplets as Microreactors for Synthesis of Mesoporous Hydroxyapatite

Microfluidic Fabrication of Monodisperse Biocompatible and Biodegradable Polymersomes with Controlled Permeability

Droplet Microfluidics for Fabrication of Non-Spherical Particles

Arrested Coalescence of Particle-coated Droplets into Nonspherical Supracolloidal Structures

Early development drug formulation on a chip: Fabrication of nanoparticles using a microfluidic spray dryer

Fabrication of Monodisperse Toroidal Particles by Polymer Solidification in Microfluidics

Asymmetric functionalization of colloidal dimer particles with gold nanoparticles

Self-Assembly of Spherical Particles on an Evaporating Sessile Droplet

Non-stick water

Superficial Wrinkles in Stretched, Drying Gelatin Films

Mechanics of Interfacial Composite Materials

Gravitational Stability of Suspensions of Attractive Colloidal Particles

Elasticity of Floppy and Stiff Random Networks

Infochemistry: Encoding Information as Optical Pulses Using Droplets in a Microfluidic Device

Shock-driven jamming and periodic fracture of particulate rafts

Colloidal spheres confined by liquid droplets: Geometry, physics, and physical chemistry

Measuring Dynamics and Interactions of Colloidal Particles with Digital Holographic Microscopy

Self-Assembly of Polyhedral Hybrid Colloidal Particles

Surfactant-Assisted Synthesis of Uniform Titania Microspheres and Their Clusters

Self-Organization of Bidisperse Colloids in Water Droplets

Design and Synthesis of Model Transparent Aqueous Colloids with Optimal Scattering Properties

Structural properties of the sliding columnar phase in layered liquid crystalline systems

Jamming at zero temperature and zero applied stress: The epitome of disorder

Measurements of the yield stress in frictionless granular systems

Comparison of low-amplitude oscillatory shear in experimental and computational studies of model foams

Tuning jammed frictionless disk packings from isostatic to hyperstatic

Minimal Energy Packings and Collapse of Sticky Tangent Hard-Sphere Polymers

Force Distributions near Jamming and Glass Transitions

Velocity Profiles in Repulsive Athermal Systems under Shear

Contact percolation transition in athermal particulate systems

Topology of force networks in compressed granular media

Short-range order and near-field effects on optical scattering and structural coloration

New directions in mechanics

Creasing instability of elastomer films

Measuring the elastic modulus of microgels using microdrops

Novel Colloidal Interactions in Anisotropic Fluids

High-throughput injection with microfluidics using picoinjectors

Air-bubble-triggered drop formation in microfluidics

Syringe-vacuum microfluidics: A portable technique to create monodisperse emulsions

Monodisperse Gas-Filled Microparticles from Reactions in Double Emulsions

Universal non-diffusive slow dynamics in aging soft matter


Patterned Colloidal Coating Using Adhesive Emulsions

Inverted and multiple nematic emulsions

Osmotic pressure and viscoelastic shear moduli of concentrated emulsions

Micro!uidic fabrication of smart microgels from macromolecular precursors

Functionalized glass coating for PDMS microfluidic devices

Structure of adhesive emulsions

Droplet-Based Microfluidics for Emulsion and Solvent Evaporation Synthesis of Monodisperse Mesoporous Silica Microspheres

Rheology of attractive emulsions

Colloidosomes: Selectively Permeable Capsules Composed of Colloidal Particles

Interactions between surfactant-coated surfaces in hydrocarbon liquids containing functionalized polymer dispersant

Self-Assembled Polymer Membrane Capsules Inflated by Osmotic Pressure

Biocompatible surfactants for water-in-fluorocarbon emulsions

Self-assembled Shells Composed of Colloidal Particles: Fabrication and Characterization

Amphiphilic Crescent-Moon-Shaped Microparticles Formed by Selective Adsorption of Colloids

Colloid Surfactants for Emulsion Stabilization

Synthesis of Nonspherical Colloidal Particles with Anisotropic Properties

Gravitational Stability of Suspensions of Attractive Colloidal Particles

Surface roughness directed self-assembly of patchy particles into colloidal micelles