Mid-IR spectroscopy monitors UV-curable adhesive dynamics

Because many industrial and biological processes require monitoring of spectral events on a range of timescales, QCL-based mid-IR spectrometers can span milli- to microsecond time scales to monitor events such as curing dynamics of light-curable adhesives

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Real-time measurements of spectral characteristics of many fast-curing adhesives and coatings are often limited by the measurement speed of off-the-shelf spectroscopy instruments. But by using quantum-cascade laser (QCL)-based frequency comb technology, engineers at IRsweep (Stäfa, Switzerland) can monitor the curing characteristics of adhesives and coatings on microsecond to minute time scales.

The IRis-F1 spectrometer, fitted with a diamond attenuated-total-reflection (ATR) accessory, was used, for example, to monitor an ultraviolet (UV)-triggered adhesive with a known uncured 1613 cm-1 infrared band that transitions into a 1638 cm-1 band after curing. After acquiring an initial background measurement upon cleaning the ATR crystal, the UV adhesive was applied to the sample plate and IRis-F1 measurements were taken in 25 ms increments before, during, and after curing with the UV source. Using a QCL with a 1585–1645 cm-1 source set to 4 cm-1 resolution and 1 ms acquisition time with 40 Hz repetition rate, raw spectra clearly show decay in the 1610 cm-1 band as the 1640 cm-1 band grows. A Fourier transform removes the interference fringes from the ATR and simple difference spectra are obtained by subtracting the uncured baseline spectrum. By fitting the growth and decay of spectra when the lamp is turned on, the kinetic properties of the curing process can be determined. Reference: https://irsweep.com/2019/04/24/monitoring-rapid-curing-reactions-with-the-iris-f1.

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