Pulsed NMR: T1 and T2 Relaxation Times of Curing Epoxy

[s_stylie0728]

I'm currently in an advanced laboratory for physics majors, and I'm conducting a pulsed NMR experiment. My partner and I decided that we we're going to measure the T1 and T2 times of Epoxy. The idea is to explore the relationship between curing epoxy and changing T1 and T2 times. We have results to compare to, and they show that T1 increases slightly (by a factor of 1.6) while T2 shortens 27 times more than T1. This is over a three hour curing time, with measurements taken every 30 minutes.

We did obtain data that seems to follow these trends, only our epoxy cured faster than theirs.

My question to any of you who might have some insight is about the physics and chemistry occurring here. Within this experiment we've done tests showing how the concentration of paramagnetic ions and viscosity can affect T1 and T2, but as far as phase changing goes, I don't have a clear idea.

Do any of you have any ideas, recommendations, reading suggestions, or anything that might give me a clue as to how the spin-lattice and spin-spin interactions are being affected here?

Thanks in advance!

 

[Ygggdrasil]

I'm not an expert at NMR, but if I remember correctly, T1 and T2 have a different dependence on the molecular correlation times (how fast the molecules tumble in solution) of the molecules you're measuring. Because T1 relaxation is stimulated most by motions on the order of your Larmor frequency (since motions at this frequency will cause B-field fluctuations that can cause stimulated emission). Therefore, T1 has a minimum when the rate of molecular tumbling is about equal to the Larmor frequency but increases as you go to either slower or faster tumbling rates. T2 relaxation, however, depends mostly on low frequency motions (since faster motions would tend to help average out the inhomogeneities that lead to decoherence). Therefore, short tumbling times (i.e. fast molecular motions) give a longer T2 times than long tumbling times (i.e. slow molecular motions). As your epoxy cures, epoxy molecules react to form larger molecules and also the overall viscosity of the solution increases; both effects will tend to increase molecular correlation times.