Alfatest è lieta di sponsorizzare la seconda edizione del congresso Milan Polymer Days,un evento internazionale dedicato alle novità nel campo della scienza e tecnologie dei polimeri.
Vi consigliamo la presentazione del ns. specialista in reologia Maurizio Lugli.
Rheological behavior of visco-elastic materials: innovative measurement techniques as an alternative to rotational rheometers.
Using a DLS (Dynamic Light Scattering) or a DWS (Diffusing Wave Spectroscopy) system, rheological behavior of viscoelastic materials can be characterized detecting the Brownian motion of the particles dispersed in the fluid to be measured. The detection of the particles motion allows the calculation of the MSD (Mean Square Displacement) and, using the generalized Stoke-Einstein equation, the rheological parameters can be derived. The measurement is done with the sample at rest, no external shear stress is applied at all, making the technique ideal for measurement at zero shear rate. When the size of dispersed particles is well known it is possible to derive the typical, absolute rheological parameters values such as Elastic and Viscous modulus (G' and G"). When the size of particles in the dispersion are unknown (most of the every day dispersion or emulsion based materials), relative values can be calculated and defined as rheological indexes.
Another alternative technique to rotationnal rheometry is the use of a microfluidic chip based technology: small quantities of fluid sample are co-eluted with a reference liquid through a capillary Y shaped channel. The two liquids, injected in their own inlet,, will join in the main slit channel where a laminar flow is generated. The laminar flow will not allow the mixing of the two liquids, each liquid will occupy a section of the slit according to its viscosity and flow rate. The unknown viscosity of the sample can be calculated directly without knowing the shear rate and shear stress applied, just knowing the reference viscosity and the flow rates involved. The measurement can be done over a wide range of high shear rates applied to the sample.
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