Helping nanoparticles ease the (surface) tension with light scattering analysis

Helping nanoparticles ease the (surface) tension with light scattering analysis

Have you ever seen pictures of people floating effortlessly on the surface of the Dead Sea? That’s because mixing salt into the water increases its surface tension, making it difficult to cross the ‘barrier’ between the surface and the water.

But what if you wanted the opposite effect? That’s where surfactants come in: nanoparticles stabilized in colloids that help break down this surface tension. These nanoparticles are everywhere. Surfactants in laundry detergent help move oils and fats from clothes to the surface. In mayonnaise, eggs contain natural surfactants that make emulsions possible, allowing oil and water to mix. And even our lungs contain surfactants that allow oxygen and carbon dioxide to be exchanged at the blood-air barrier in the alveolar cells.

From detergents to food to medicines, surfactants are key to many products and innovations. But the history of their use illustrates the importance of proper analytical techniques. To take detergents as an example, the first synthetic detergents were made from branched-chain surfactant nanoparticles that microbes couldn’t break down – leading to pollution of natural environments. With the proper analysis, this risk could have been detected before these detergents went into production.

As the use of surfactants increases in many applications, reliable and efficient instrumentation is therefore essential to optimize their effectiveness and ensure safety for people and the environment.

Light scattering: The solution for stable surfactant nanoparticles

Light scattering is the staple technique for obtaining three key measurements for optimizing the stability and efficacy of these nanoparticles. These are molecular size and weight, particle size, and in particular, zeta potential. Zeta potential is a physical property of particles in suspension that indicates long-term particle stability. It can be used to predict interactions with surfaces, optimize suspension formulations of emulsions and protein solutions, and maximize efficiency in film and coating formation.

There are several types of light scattering analysis including: dynamic light scattering (DLS), static light scattering (SLS), electrophoretic light scattering (ELS), and Multi-angle dynamic light scattering (MADLS).

  • In DLS, a laser is fired through a polarizer and into a sample. All the molecules in the solution are hit by the light, and as a result the light is diffracted in all directions, with the diffracted beams creating a speckle pattern. It is then possible to calculate the shapes and sizes of the nanoparticles and molecules that ‘scattered’ the light.
  • SLS starts in the same way, but instead of calculating shape and size from a speckle pattern, molecular weight is measured by observing the intensity of the scattered light. As described by Rayleigh’s theory, molecular weight and size are proportional to the ratio of scattered light intensity to incident light intensity.
  • During ELS, an electric field is applied across the colloid to calculate the zeta potential of the particles within. In an electric field, particles with a zeta potential will migrate toward the electrode of opposite charge at a rate proportional to the magnitude of the zeta potential.
  • Multi-angle dynamic light scattering, or MADLS, combines the scattering angle information from Mie theory and the particle size distribution analysis from a dynamic light scattering measurement in an integrated method. The lower noise, and hence reduced smoothing, enables a more reliable and accurate representation of the particle size distribution, with improved characterization of individual components of a multi-component sample.

The knowledge gained from these measurements allows researchers and manufacturers to improve their surfactants in many ways, from optimizing their properties to achieve the best results, to ensuring that the nanoparticles are easily broken down and leave no trace in the target environment.

Light scattering made easy with the Zetasizer

Not surprisingly, the calculations behind these measurements are highly complex, and all three techniques are necessary to obtain a complete characterization of a surfactant. As such, instruments that perform these calculations automatically have revolutionized colloidal research.

And the Zetasizer Advance series offers this automation for all three techniques! Instead of requiring experts for each type of measurement, or manual calculations, the Zetasizer allows users to quickly obtain accurate and reliable measurements with minimal training. What’s more, an innovation for the Zetasizer will be unveiled in April 2024 that will truly take its benefits to the next level – minimizing its footprint in workflow processes and freeing researchers and technicians for other tasks! Surfactant research and production will be easier and safer than ever before.

Curious about the latest innovation for the Zetasizer? Be sure to sign up for the reveal webinar!

And stay tuned for our next colloids blog, where we’ll dive into nanoparticle tracking analysis!