The creation of emulsions is necessary in many industries, perhaps most notably cosmetics and food.
For far more information than you ever wanted to know about emulsification, and various technical aspects of homogenization technologies used in emulsification, there’s a very comprehensive document created by Jochen Weiss from the University of Hohenheim which you can find here. The focus is more on process-scale homogenization than laboratory scale, but the information contained within is mostly applicable to both.
High-pressure homogenizers, rotor-stators, and ultrasonic homogenizers are generally the most appropriate instruments for creating emulsions.
|Homogenizer Technology||Minimum Average Particle Size (approximate)*|
|High-Pressure||100 nm (1 x 10-7 m)|
|Rotor-Stator||3 µm (3 x 10-6 m)|
|Ultrasonic||100 nm (1 x 10-7 m)|
*Particle sizes may vary based on processing time, equipment used, and substances being processed. The actual achievable particle size in any given application and under any given conditions most often needs to be empirically determined.
High-pressure homogenizers are the type used by the dairy industry, and are suitable for many emulsification applications. When looking at high-pressure homogenizers, the key consideration is the homogenization valve geometry. The tighter the value or the smaller the pore size, the larger the pressure drop will be. A larger pressure drop provides more shear forces, more cavitation, and ultimately a smaller particle size. The smaller the particle size, the more homogenous and more stable your emulsification will be. Due to the relatively high cost and large size of high-pressure homogenizers, they are most appropriate for larger applications (on the scale of liters or more). They are also the best choice for high-viscosity emulsions, as the requirement for most high-pressure homogenizers is simply that the liquid can be pumped.
Rotor-stator homogenizers are suitable for just about any emulsification application that does not require a very small particle size. Rotor-stators can be found for a huge range of volumes, from microliters up to large-scale industrial applications. Look at the probes available with the unit you are considering, and ensure that they can handle the desired volume range.
Ultrasonic homogenizers are highly efficient at creating emulsions for smaller volumes (single-digit liters or below). If you project your emulsification to be difficult, be sure to look at the amplitude of the horn. Higher amplitudes are more efficient than smaller amplitudes. Note that larger horns can handle larger volumes but have lower amplitudes, so it is preferable to get a more powerful unit with a smaller but higher amplitude horn than a less powerful unit with a larger horn. Note: Ultrasonic homogenizers will deposit trace amounts of titanium into your sample, and therefore should not be used for applications involving a product intended for human consumption.
If selecting a rotor-stator or ultrasonic homogenizer, be sure to keep viscosity in mind. As viscosity increases, homogenization efficiency decreases. If you have a viscous sample, choose a unit which has a maximum rated volume significantly higher than your application volume without going under the minimum rated volume for the unit. Depending on the viscosity of the substance, you may need a system whose rated maximum volume is 5 to 10 times your sample size.