Rheo-Raman | Combining Rheology and Raman Spectroscopy: Following an Epoxy Resin Curing Reaction

The combination of an MCR series rheometer and a Cora 5001 Fiber Raman spectrometer offers unique opportunities in measuring both physical and chemical properties of a system simultaneously as presented in the following report for an epoxy curing reaction.

Rheometers are excellent tools to characterize and follow the change in physical parameters of various samples during some processes or under specific environmental conditions. In the case of a chemical reaction, further insight can be gained by simultaneous acquisition of chemical information by coupling the rheometer with a Raman spectrometer.

An example for a process during which both the physical and chemical properties of a sample change simultaneously is the curing reaction of an epoxy resin. It involves the gradual changes in viscosity and elasticity as a direct consequence of the chemical reaction in which the epoxy and hardener are converted into a three-dimensional network of the desired properties via crosslinking. This can be monitored using Raman spectroscopy as functional groups are consumed during crosslinking resulting in decreasing signals in the Raman spectra.

The combination of rheology and Raman spectroscopy presented here offers the advantage of simultaneous measurements triggered by the rheometer for both instruments. Thus, both viscoelastic and spectroscopic data share a common time axis. Therefore, it is straightforward to correlate the information gain between the two techniques.

When comparing chemical and physical data of the same reaction, it becomes evident that the chemical reaction progress precedes changes in the physical properties of the material. This is because the macroscopic properties, as measured by the rheometer, will change only after a substantial amount of epoxy groups has reacted resulting in a transition between the liquid and gelatinized solid, whereas usually the chemical reaction is progressing mainly at a constant rate.

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