High-resolution Imaging of Double Emulsion

High-resolution observation

An emulsion is a solution where two different liquids that do not dissolve into each other, such as oil and water, separate into two layers due to the interfacial tension effect.

In recent years, notably in the areas of cosmetics and food, emulsions have been in focus for their ability to control skin affinity, appearance, and texture. In cosmetics, the use of emulsions has spread to moisturizing creams and serums. In the area of food processing, research into the application of emulsions is progressing in order to control the flavor of foods.

Amid such trends, the methods for evaluating emulsions are also being researched. Particle size measurement and condition assessment of emulsions have garnered much attention and interest, thereby contributing to the identification of the issues in actual evaluations.

In this section, we introduce an application for double emulsion, which has come into the spotlight.

Larger emulsifying particles tend to strengthen the characteristics, such as richness and aroma, of milk constituents. Therefore, the flavor, including taste, can be controlled by adjusting the size of the emulsifying particles.

On the other hand, since emulsifying particles are lipids, making them larger increases the costs proportionally. It also increases the caloric content of these particles, which may make the products less desirable as the current trend favors low-calorie products.

Double emulsion is an approach that resolves the above issues. Encapsulating water inside emulsifying particles increases the size of the emulsifying particles but still keeps the total use of lipids down. This contributes to reductions in both costs and calories.

However, expertise is required to stably produce a double emulsion. It may be difficult to adjust the conditions correctly to produce double emulsions. A double emulsion may be lost with heat treatment. The bar is still high for stable production and maintaining the emulsion until consumption.

A

Outer water phase

B

Oil droplet

C

Oil phase

D

Inner water phase

E

Water phase

Conventional problems

Microscopic observations are needed to check what is actually happening and under what conditions, for example, to set stable production conditions and to examine the emulsion’s state after different treatments.

Nevertheless, such observations were difficult due to the minuscule size of the water capsules in double emulsions. These capsules are only several hundred nanometers across, and ordinary optical microscopes do not have the resolution to enable such observations. While an electron microscope is capable of observation of this size, doing so is difficult due to the object being water.