Droplet generator

Droplet generator to generate droplets accurately

In order to work with fluids on a very small scale, microsized droplets are often used. These droplets are always the same, making them easy to work with. To make these droplets, a droplet generator can be used. These generators can be tuned to make almost any type and size of droplets. Compared with traditional methods, a droplet generator is much more precise and faster. And because the droplet generator can generate droplets with a high repeatability, there is almost no downside to them. This technology is therefore very exciting and offers new potential when droplets are needed in large quantities.

Inner workings of a droplet generator

There are two distinct types of geometry used in the production of droplet: focused flow and T-junction. Both types have their advantages and the choose between the two depends largely on the type of fluid that is used. However, generally speaking the focused flow geometry is used with higher flow rates, because the forming of droplets is more stable. But there are much more factors that influence this decision than just the flow rate. The following must be taken into consideration:

  • Dimensions of channels and their geometry
  • Stability of flow rate actuation
  • Flow rates of the fluid used
  • Hydrophobic or hydrophilic channels
  • Viscosity and surface tension
  • And more

Different kinds of droplets

A droplet generator can be tuned to create different kinds of droplets. By changing the relative viscosities, surface tension and velocities between the dispersed droplets and the continuous droplets the size of the droplet can be influenced. The generators can also be coated in such a way that either oil-in-water droplets are generated, or water-in-oil droplets. By coating the generator’s channels in a hydrophobic coating, water-in-oil droplets can be made. Normal generators, without coating, are capable of producing oil-in-water droplets.


The benefits of a droplet generator

Producing small droplets of fluid can be a tedious process, which is hard to get right consistently. The conventional methods are usually slow and inconsistent, which is why using a droplet generator is quite an advancement. These generators are small chips, which cleverly use small channels to modify fluids. And because they work on a very small scale, the results are always the same, resulting in very highly reproducible droplets. A droplet generator is therefore an excellent replacement for conventional methods. It is smaller, more reliable and faster in almost every situation.

Parameters of a droplet generator

As said before, a droplet generator uses channels to modify fluids to form droplets. Usually a generator starts with a larger droplet of the fluid used in the generator. This is then split using precisely formed channels, that basically forms the bigger droplet into a smaller one. This process can then be repeated to generate smaller droplets. Of course, the real dynamics of this process are more complicated than described here. Using several parameters the size of the droplets can be adjusted. Usually the relative viscosities, surface tension, and velocities between the dispersed and the continuous phase droplets are adjusted to produce different sizes of droplets. Of course this does depends on the kind of liquid used.


Another important factor that has to be taken into consideration is the flow rate of the liquid used. There are two important types of geometry that droplet generators are designed with. These two types are focused flow and T-junction. The choice between these two depends on many variables, but the important difference between them is how they react to flow rates. A T-junction is often used with slow flow rates, whereas the focused flow geometry tends to provide a more stable droplet production at higher flow rates.


The advantages of a droplet generator

A droplet generator is an essential tool when droplets are needed with high precision and in rapid succession. These generators are small chips, which use small channels to generate small droplets of a liquid. Compared with conventional methods they are much more precise and have a higher repeatability. Also, because of their size, these devices offer a lot of opportunities in terms of applications. They can be tuned to be used with different liquids and create different droplets.

Adjusting the droplet generator

A droplet generator can be made to be used with many different kinds of microfluidics and flow rates. Using the relative viscosities, surface tension, and velocities between the dispersed and the continuous fluid droplets of almost any size can be created. Using a hydrophobic coating, water-in-oil droplets can be created. Without coating oil-in-water droplets can be generated directly with normal glass chips and the droplet generator technology. There are two types of geometry used in these generators: T-junction and focused flow. Focused flow is best used in high flow rate systems, whereas T-junction is mostly used in low flow rate systems.

Parallel systems

Because these generators are so small, incorporating multiple on one chip can be done easily. This allows for systems that were previously not possible at this size. One of the most promising developments in this field is the use of droplet generators to create a emulsion that can dispersed in a controlled fashion. Because the generators have such delicate channels and systems, the dispersion of this emulsion is unparalleled by almost anything, especially at this size. This technology is therefore very promising and will continue to grow. Because of the easy use of water-in-oil and oil-in-water droplets, several emulsification systems can benefit from this technology.