Hi,
I am using Malvern's Zetasizer to get the rheological properties of the hydrogel formed with Phytagel containing silica beads entrapped in the said hydrogel. When I am taking the readings using the Zetasizer, I am supposed to create a SOP stating the nature of the particles used and the Dispersion medium. Is it alright, if I choose water as the dispersion medium? As, the whole goal is to find out the properties of the Phytagel hence I can't insert properties being asked in the SOP for Phytagel (such as viscosity, refractive index and Dielectric constant).
Richa Ghosh I am a little confused by your question and also the nature of your particulate system. The Malvern Zetasizer does not measure rheological properties in any way. It uses dynamic light scattering (DLS) via the diffusion coefficient to calculate particle size and (if you also have the zeta option) the electrophoretic mobility of particles under an electrical field. In DLS, for the intensity distribution, we only require the refractive index of the continuous phase (the liquid within which the particles reside). There is no requirement for the optical properties of the particles themselves; the RI of the particles is only required for the (Mie) transformation from intensity to volume. If you need rheological performance, then you’d use a rheometer. In terms of movement then the viscosity term is inherent in the Stokes-Einstein equation relating hydrodynamic size to the (measured) diffusion coefficient. It’s obvious that in ‘thicker’ media particles will travel more slowly.
In both size and zeta potential cases, a movement is measured, so if you have beads trapped within a matrix, I can’t see how you can have much movement. So, please explain in detail how your system is constituted so we can understand exactly what you’re trying to achieve. If you have particles of a known size within a system, you can use this route to calculate the viscosity of a system where this would be otherwise difficult to do. In brief what are you trying to measure and is your hydrogel a viscous continuous phase?
Hi, yes I am using silica particle of known diameter. Yes, the medium is phytagel which forms crossed hydrogels and it forms continuum viscous medium.
I was asked to insert the Refractive index of the Phytagel and the dielectric constant of the Phytagel and not that of the silica particles.
Richa Ghosh Yes, you need the properties of the continuous phase for DLS to be able to correctly calculate the hydrodynamic diameter from the (measured) mobility. The Phytagel (agar substitute) RI is easily measured (Abbe refractometer) and the viscosity can also be measured or obtained from the manufacturer's data sheet. However, if you have no movement/mobility then DLS won't work...
The attached may be useful.
A webinar (free registration required) on the Abbe refractometer can be accessed at:
Uses of an Abbe refractometer
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W120626AbbeRefractometer.html
Good luck with your research!
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