3 research outputs found
Exhibitive Nano-to-Micron Scale Sedimentation Dynamics of Colloidal Formulations Through Direct Visualization
The study of sedimentation behavior of nanoparticle dispersions
is important for revealing particle size and colloidal stability characteristics.
Quantitative appraisal of real-world colloidal systems in their native state,
is key for replacing prevailing empiricism in formulation science by
knowledge-based design. Herein, we choose fuel cell inks as one case-example
amongst many other possibilities to present a new visualization technique,
called Transmittogram. This technique readily depicts the time-resolved settling
behavior of solid-liquid dispersions, measured by analytical centrifugation
(AC). Although AC enables the causal examination of agglomeration, settling, and
creaming behavior of dispersions, along with its consequent effect on structure
formation and product properties, the understanding of the main transmission
readout is often non-intuitive and complex. Transmittograms are, therefore, the
missing link for straightforward data interpretation. First, we illustrate the
utility of transmittogram analysis using model silica nanoparticle systems and
further validate it against known characteristics of the system. Then, we demonstrate
the application of transmittograms to characterize fuel cell inks, showing the
strength of the approach in deconvoluting and distilling information to the
reader. Finally, we discuss the
potential of the technique for routine analysis using analytical centrifugation.<br /
Towards a Framework for Evaluating and Reporting Hansen Solubility Parameters: Applications to Nano and Micron Scale Particle Dispersions
A thorough understanding of complex
interactions within particulate systems is a key for knowledge-based
formulations. Hansen solubility parameters (HSP) are widely used to assess the
compatibility of the dispersed phase with the continuous phase. At present, the
determination of HSP is often based on a liquid ranking list obtained by
evaluating a pertinent dispersion parameter using only one pre-selected characterization
method. Furthermore, one cannot rule out the possibility of subjective judgment
especially for liquids for which it is difficult to decipher the compatibility
or underlying interactions. As a result, the end value of HSP might be of
little or no information. To overcome these issues, we introduce a generalized
technology-agnostic combinatorics-based approach. We discuss the principles of
the approach and the implications of evaluating and reporting particle HSP
values. We demonstrate the approach by using SiNx particles synthesized in the gas phase. We
leverage the analytical centrifugation data to evaluate stability trajectories
of SiNx dispersions in various liquids to deduce particle-liquid
compatibility. </p
On the State and Stability of Fuel Cell Catalyst Inks
Catalyst layers (CL), as an active component of the catalyst coated membrane (CCM), form the heart of the proton electrolyte membrane fuel cell (PEMFC). For optimum performance of the fuel cell, obtaining suitable structural and functional characteristics for the CL is crucial. Direct tuning of the microstructure and morphology of the CL is non-trivial; hence catalyst inks as CL precursors need to be modulated, which are then applied onto a membrane to form the CCM. Obtaining favorable dispersion characteristics forms an important prerequisite in engineering catalyst inks for large scale manufacturing. In order to facilitate a knowledge-based approach for developing fuel cell inks, this work introduces new tools and methods to study both the dispersion state and stability characteristics, simultaneously. Catalyst inks were prepared using different processing methods, which include stirring and ultrasonication. The proposed tools are used to characterize and elucidate the effects of the processing method. Structural characterization of the dispersed particles and their assemblages was carried out by means of transmission electron microscopy. Analytical centrifugation (AC) was used to study the state and stability of the inks. Herein, we introduce new concepts, S score, and stability trajectory, for a time-resolved assessment of inks in their native state using AC. The findings were validated and rationalized using transmittograms as a direct visualization technique. The flowability of inks was investigated by rheological measurements. It was found that probe sonication only up to an optimum amplitude leads to a highly stable colloidal ink.</p