The Importance of Nanoparticle Size Measurement Using Dynamic Light Scattering
Advanced nanomaterials are powering the future of electronics. But ensuring even nanoparticle size and distribution is crucial for maximizing the performance of these materials.
Nanomaterials are having a major impact on modern technologies. These remarkable materials, some occurring naturally, others precisely engineered to perform a specific function, are those for which a single unit can be measured in the nanoscale. For context, a nanometer is one millionth of a millimeter, roughly 100,000 times smaller than the diameter of a human hair. Because of this tiny particle size, nanomaterials often have unique physical and chemical properties compared to bulk materials.
The European Commission defines a nanomaterial as a “material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1–100 nm.”[1] That definition encompasses a wide range of materials, including carbon nanotubes, fullerenes, and other advanced materials like quantum dots. Such materials created by engineers for functional purposes are known as engineered nanomaterials (ENMs), and they can be found in products as diverse as consumer electronics, car tires, and even sunscreen.
One of the main methods for measuring nanoparticle size is dynamic light scattering (DLS), a technique used by XTPL and other nanomaterial specialists to validate functional materials. This article goes over the basics of dynamic light scattering and why it is crucial to the success of nanomaterials like highly conductive nanoinks.
The Importance of Nanoparticle Size for Nanomaterials
There are many diverse advantages to nanomaterials, but these vary depending on the specific nanomaterial and its application. For example, some nanomaterials are highly useful in areas like biotechnology, while others are deployed in cutting-edge consumer electronics due to their desirable electrical or magnetic properties.
However, the utility of nanomaterials depends a great deal on the size and distribution of each nanoparticle: inconsistent sizing or density results in unpredictable behavior. In fact, as the European Commission definition notes, a material ceases to become a true nanomaterial if less than half of its constituent particles measure 1–100 nm. Consequently, precise measurement of nanoparticle size is an important stage in the development of ENMs that guarantees the effectiveness of the material.
The importance of nanoparticle size often comes down to the ratio between surface area and volume. The smaller the particle size, the greater this ratio, which has a positive effect on characteristics like reactivity, strength, and catalytic behavior. Additionally, particle size uniformity can reduce the chances of defects in final parts: variations in nanoparticle size and shape often lead to uneven packing and porosity in nanoparticle materials, and this can lead to the formation of internal stresses and defects when these materials are processed using the chosen manufacturing method. These flaws can ultimately result in cracks and limit final material strength.
Researchers have highlighted the importance of nanoparticle size in areas like biomedicine, noting that particle size “plays a central role in determining material properties and performance in biomedical applications.”[2] These applications include, but are not limited to, functional nanomaterials developed for the monitoring of biochemical activity, control of biological functions, and therapeutic applications.
Nanoparticle Distribution
Nanoparticle distribution is as important as nanoparticle size (and shape) for ensuring high material performance, so material developers can use various techniques to ensure even distribution. For example, controlling particle interactions through dispersants and using monodisperse colloids like stabilized silica can improve uniformity and prevent particles clumping together.
Measuring Nanoparticle Size With Dynamic Light Scattering
Dynamic light scattering (DLS) is a scientific technique used to measure the size of small particles in a suspension. It does this by shining a laser on the particles suspended in a liquid (such as silver particles within a conductive nanoink). As the particles move within the suspension through Brownian motion, they scatter light. Usefully, this scattered light fluctuates over time, so DLS analyzes these fluctuations to determine how fast the particles are moving—smaller particles move faster, larger ones move slower. After registering the speed of particle movement, the Stokes-Einstein equation can be used to calculate the average particle size.
In practical terms, conducting DLS analysis of a nanomaterial involves specialized equipment and conditions. Scientists first prepare a liquid sample of nanomaterials, ensuring it is well dispersed—sometimes using an ultrasonic bath—and free of dust. They place the sample in a cuvette (a straight-sided clear container) inside a DLS instrument such as a Malvern Zetasizer Advance or Zetasizer Ultra, which shines a laser through it. As the nanoparticles move, they scatter the light, and a detector on the instrument measures how this scattered light changes over time. The instrument uses this data to calculate how fast the particles are moving, then uses that speed to determine the average particle size.
The DLS process works well because it is simple and non-destructive. However, it is not the only means of measuring nanoparticle size. For example, another method, based on different principles, is Transmission Electron Microscopy (TEM).
DLS and TEM are both used for measuring particle size, but they use different underlying principles and do not technically measure the same thing. DLS measures the hydrodynamic size of particles in suspension (including both the particle and its surrounding solvent layer) whereas TEM measures the physical size of individual particles only. Both methods can be useful, but this difference can lead to discrepancies in size measurements, especially for aggregates or particles with surface layers.
The table below outlines the basic differences between DLS and TEM, as well as an example of results obtained for an XTPL nanoink.
| Dynamic Light Scattering (DLS) | Transmission Electron Microscopy (TEM) | |
|---|---|---|
| Method | Light scattering | Electron beam |
| Measurement Objective | Hydrodynamic size | Physical size |
| Resolution | Lower | Higher |
| Measured nanoparticle size (nm) for XTPL Au Nanopaste 90 | 80–130 | 35–55 |
Characteristics of XTPL Nanomaterials
By using methods such as dynamic light scattering to measure nanoparticle size in its advanced functional nanoinks and nanopastes, XTPL is able to develop reliable materials suited to consumer electronics, healthtech, automotive, and other industries. In short, these techniques allow XTPL to catch agglomerates, check for consistency, and improve quality control during material R&D, resulting in a superior final product.
Additionally, even and consistent particle size distribution makes nanomaterials easier to print via extrusion or direct ink writing (DIW) techniques, including those such as XTPL’s own Ultra Precise Dispensing (UPD) method. This is because uniform particle sizes lead to better flow behavior and stability of the ink or paste—properties that are important for smooth and consistent printing. By using DLS, XTPL ensures that its nanopastes and nanoinks can be printed with a high level of accuracy and then perform as expected in advanced applications like flexible electronics, quantum dot displays, and medical devices.
Resources
[1] Rauscher H, Roebben G, Mech A, Gibson N, Kestens V, Linsinger TP, Sintes JR. An overview of concepts and terms used in the European Commission’s definition of nanomaterial. Publications Office of the European Union. 2019:1-44.
[2] Dolai J, Mandal K, Jana NR. Nanoparticle size effects in biomedical applications. ACS Applied Nano Materials. 2021 Jul 2;4(7):6471-96.
