Comprehensive Characterization of Nano- and Microparticles by In-Situ Visualization of Particle Movement Using Advanced Sedimentation Techniques

This paper's title was written by Professor D. Lerche and published as open-source in the KONA Powder and Particle Journal.

You can download a free copy of the article using this secure link.

Alternatively, you can go to the KONA Powder and Particle Journal, where you can search for the paper and find many other excellent publications.

Research Topic:

Dietmar comprehensively reviews STEP-Technology and all its applications in suspension, emulsion, and particle size analysis.

Paper Highlights:

If you want to learn more about the STEP-Technology and its applications, please consider reading the publication. Hopefully, for those who do not have the time to read everything, this short mile-high overview will steer you to the most helpful pages.

Section 1. Introduction.

A brief review of the various particle sizing principles and techniques.

Section 2. In-situ visualization of particle migration - STEP-Technology®.

This section begins with a short history of commercial sedimentation techniques and then dives into a detailed explanation of the STEP-Technology®.

Figure 3 illustrates the complementary view of the evolutionary light transmission, extinction, and clarification signals measured across the entire sample and is one of STEP-Technology’s foundations.

Figure 7 displays the effect of changes in the illuminated wavelength and its impact on scattering. Lowering the wavelength allows for greater sensitivity towards nano-particles and low concentration samples.

Figure 9 is an excellent display of STEP-Technology’s ability to resolve complex and multi-modal particle size distributions. It also demonstrates its ability to analyze and differentiate between various emulsion and suspension instability mechanisms.

Section 3. Particle Sizing conforms to ISO 13317 and 13318.

This is the longest and most in-depth section covering many aspects of particle size analysis. The first focus is on some called particle velocity distributions. This term may sound unfamiliar, but the STEP-Technology® allows you to measure the creaming or sedimenting particle/droplet distribution. It is a powerful tool because it is a first principle method, and you can employ it for any system. There is no need to input any physical or material constants. The particle velocity distribution correlates directly to its particle size distribution.

Figures 10 and 11 show what kind of data you get for a four-modal particle size distribution at both non-accelerated conditions (LUMiReader®) and accelerated conditions (LUMiSizer®).

Working with non-spherical particles and high-concentration dispersions. The PVD (particle velocity distributions) allows you to characterize the actual behavior of non-newtonian dispersions and non-spherical particles and study high-concentration formulations.

Figure 15 gives you the cumulative sedimentation velocity results for a polystyrene latex suspension as a function of concentration, followed by an example of the effect of particle size and the hindrance function.

Figure 19 overlays the behavior of shear-thinning suspensions measured using a traditional rheometer and the tracer particles-based results obtained with the LUMiSizer.

Figure 22 is a critical graph showing the relation between creaming/sedimentation rates and rheology. You will sometimes hear people (competitors?) say that sedimentation or creaming-based analysis is only valid for low-concentration Newtonian systems. That is equivalent to saying you cannot circumnavigate the globe because you may run the ship ashore on an island. On the contrary, using analytical centrifugation, you can work with high concentration and non-Newtonian dispersions and obtain beneficial insights, as shown in figure 22. With the STEP-Technology® you can measure the effective yield stress, which can be a critical part aspect of shelf-life prediction

Pages 17, 18, and 19 present a deep dive into particle size analysis covering the deconvolution of the optical signal, sector-shaped versus rectangular centrifugal cells, and comparison between extinction-based, volume-based, and number-based particle size results.

You will also briefly mention a European Union nanomaterials classification study (www.nanodefine.eu). The LUMiSizer® STEP-Technology® had the lowest deviation of the mean size measured by scanning electron microscopy (SEM) compared to the disc centrifuge (CPS), analytical ultracentrifuge (UAC), and dynamic light scattering (photon correlation spectroscopy).

Page 19 discusses the ability of the multiwavelength LUMiReader® STEP-Technology® to measure volume-based particle sizes without knowing the refractive index correctly.

The remainder of the paper is devoted to showing two more applications. The first is the determination of the actual density of a dispersed material. The second is the characterization of magnetic particles.