Recent advances in in-process characterization of suspensions and slurries

In this study, the classical Stober silica synthesis protocol was used to test the limits of simplification in the preparation and size determination of nanoparticles. The scope of three-ingredient, one-pot synthesis was established in conditions of regular 96% and 99.8% ethanol as solvent, with aqueous ammonia as the only source of base and water. Particles with diameters in the 15-400 nm range can be reliably obtained with this straightforward approach, and the direct relationship between the size and the product of concentrations of water and ammonia is evidenced. Furthermore, the idea of a linear approximation for Mie scattering in particular conditions is discussed, using experimental data and theoretical calculations. A simple, fast method for particle size determination utilizing a UV-Vis spectrophotometer-an easily accessible instrument-is explained, and shows a level of error (<0.5 SD) that can be acceptable for less rigorous laboratory use of nanoparticles or serve as a quick means for testing the influence of minor alterations to known synthetic protocols. This work aims to show that nanoparticle synthesis can (and should) become a regular occurrence, even in non-specialized labs, facilitating research into their new applications and inspiring outside-the-box solutions, while discussing the drawbacks of a more relaxed synthetic regimen.

https://www.mdpi.com/1996-1944/13/14/3088/pdf

"DIY" Silica Nanoparticles: Exploring the Scope of a Simplified Synthetic Procedure and Absorbance-Based Diameter Measurements

Nanoparticles are applied in an increasing number of products (e.g. medicine, food and cosmetics). There is a need to real-time monitor the growth of nanoparticles during production inside the chemical reactor. However, standard particle sizing methods such as dynamic light scattering (DLS) and transmission electron microscopy (TEM) cannot do this. A suitable candidate may be ultrasonic transmission spectroscopy (UTS). Here, the sound speed and attenuation are measured of a dispersion and a physics based model is inverted and fitted to the measurements. The measurements have to be done with great accuracy: e.g. one should be able to measure frequency dependent variations in the speed of sound smaller than 0.05%. The measurements also have to be carried out fast enough compared to the time scale of the reaction. Moreover, the inversion has to be able to deal with the changing properties of the solvent during particle formation. Here, we report on the new ultrasound nanoparticle sizer (UNPS) that has these abilities and therefore could successfully monitor the size and concentration growth of nanoparticles during a reaction inside a reactor in real-time.

Real-Time Monitoring of Size and Concentration of Nanoparticles Inside a Reactor Using Ultrasound

Both in design and production of nanoparticles and nanocomposites it is of vital importance to have information about their size and concentration. During the formation of nanoparticles, real-time monitoring of particle size and concentration during bottom-up synthesis in liquids allows for a detailed study of nucleation and growth. This provides valuable insights into the formation of nanoparticles that can be used for process optimization and scale up. In the production of nanoparticles, real-time monitoring enables intervention to minimize the number of off-spec batches. In this paper we will qualify an ultrasound nanoparticle sizer (UNPS) as a real-time monitor for the growth of nanoparticles (or sub-micro particles) in the 100 nm-1 μm range. Nanoparticles affect the speed and attenuation of ultrasonic waves in the dispersion. The size of the change depends, amongst other things, on the size and concentration of the nanoparticles. This dependency is used in the UNPS method. The qualification of the UNPS was undertaken in two successful experiments. The first experiment consisted of static measurements on commercially available silica particles, and the second experiment was real-time monitoring of the size and concentration during the growth of silica nanoparticles in Stober synthesis in a water-alcohol mixture starting from the molecular precursor tetraethyl orthosilicate. The results of the UNPS were verified by measurements of a dynamic light scattering device and a transmission electron microscope. © 2018 by the authors.

/pdf/qualification-of-an-ultrasonic-instrument-for-real-time-3s6am274jb.pdf

Gert Jan van Groenestijn

Papers

Qualification of an ultrasonic instrument for real-time monitoring of size and concentration of nanoparticles during liquid phase bottom-up synthesis