Flow Cell Coupled Dynamic Light Scattering for Real-Time Monitoring of Nanoparticle Size during Liquid Phase Bottom-Up Synthesis

Abstract

Featured Application: A unique set-up for real-time monitoring of the size of nanoparticles during bottom-up liquid phase synthesis is presented in this article. The analysis method applied to study the size of dispersed nanoparticles during synthesis is dynamic light scattering (DLS). In contrast to conventional DLS, the DLS set-up presented in this article comprises a modulated 3D cross correlation geometry, and therefore allows accurate measurements of particle size in flow at flow rates of at least up to 17 mL·min −1 . This is essential for obtaining real-time information on the size of the dispersed nanoparticles. The DLS system could be connected to reactors of various sizes using the analysis loop presented in this article, which is coupled to a flow cell in the DLS set-up. Thus, the DLS set-up presented here is suited to study the nucleation and growth of nanoparticles in dispersion, facilitates a rational scale-up, and allows intervention in the production process of nanoparticle dispersions to minimize the number of off-spec batches.Abstract: To tailor the properties of nanoparticles and nanocomposites, precise control over particle size is of vital importance. Real-time monitoring of particle size during bottom-up synthesis in liquids would allow a detailed study of particle nucleation and growth, which provides valuable insights in the mechanism of formation of the nanoparticles. Furthermore, it facilitates a rational scale-up, and would enable adequate intervention in the production process of nanoparticle dispersions to minimize the number of off-spec batches. Since real-time monitoring requires particle size measurements on dispersions in flow, conventional dynamic light scattering (DLS) techniques are not suited: they rely on single scattering and measure the Brownian motion of particles dispersed in a liquid. Here, we present a set-up that allows accurate measurements in real-time on flowing dispersions using a DLS technique based on modulated 3D cross-correlation. This technique uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. We connected the reactor to a flow-cell in the DLS equipment using a tailor-made analysis loop, and successfully demonstrated the complete set-up through monitoring of the size of spherical silica nanoparticles during Stöber synthesis in a water-alcohol mixture starting from the molecular precursor tetraethyl orthosilicate.

Quid Pro Flow

“…By moving the analytical probe or having multiple analysis points, reaction kinetics or pathway can be elucidated, given that flow path length = time under continuous conditions . As analytical chemistry offers increasingly rapid and sensitive measurements, more techniques are being incorporated into flow processes: LC, GC, , MS, , particle sizing, IR, , optical methods, and NMR , are more established, but more recently PXRD, , optical emission spectroscopy, SAXS/WAXS, − 3D microscopy, magnetometry, and even single crystal XRD have been reported as inline or online methods. In each case, the method must be optimized for the desired analyte, concentration, and sensitivity required …”

Microfluidic in-line dynamic light scattering with a commercial fibre optic system

“…where ω is the beam radius at the focus, and v is flow velocity. Given the restrictions highlighted in eqn ( 5) and (7), several previous flow-DLS setups were designed with large (≳1 cm) flow cells 4,5,[7][8][9][10] such that, at a given flow rate, both the velocity and shear rate become relatively small and their respective decorrelation contributions can be neglected (or the transit term accounted for).…”

“…Dynamic light scattering (DLS) is a ubiquitous experimental technique used to characterise the hydrodynamic size of particles and relaxation processes in simple and complex systems. [1][2][3] Given its extensive use in biology, physicalchemistry and soft matter science, a number of authors have considered both the theoretical and experimental feasibility and implementation of DLS under flow for particle size measurements, [4][5][6][7][8][9][10][11] flow velocity and shear determination, [12][13][14][15][16][17] and recently, also coupling with microfluidics. 16,[18][19][20] Various technical challenges in flow-DLS have been identified, pertaining to optical alignment of the scattering and flow planes, 11,16 and limitations on the flow velocity relative to particle diffusion, 4,5,12 respectively giving rise to shear flow and transit contributions to the scattering signal, which require complex data analysis, by contrast to that of conventional DLS.…”

Qualification of an Ultrasonic Instrument for Real-Time Monitoring of Size and Concentration of Nanoparticles during Liquid Phase Bottom-Up Synthesis

“…of the growth of nanoparticles in real time [17]. In the developed DLS set-up, the sensors are not measuring directly in the reactor, but an analytical bypass loop is used for sampling purposes.…”

“…Furthermore, DLS methods are not able to measure concentration. Recently, we have successfully developed a flow cell coupled DLS set-up that also allows monitoring of the growth of nanoparticles in real time [17]. In the developed DLS set-up, the sensors are not measuring directly in the reactor, but an analytical bypass loop is used for sampling purposes.…”