In Situ FT-IR Analysis of a Composite Curing Reaction Using a Mid-Infrared Transmitting Optical Fiber

Abstract

The use of a mid-infrared transmitting fiber to carry the infrared beam of an FT-IR spectrometer outside of the optical bench is reported. In addition it is demonstrated that it is possible to analyze samples using the fiber as an internal reflection element. The fiber is covered with a protective coating which can be removed for a short region, to allow contact with the sample over a controlled length. Two examples of the use of an optical fiber for remote sampling are discussed. The first shows that a spectrum of a liquid sample (2-butanone) can be easily measured, and the second shows how a fiber can be used to monitor the progress of curing reactions in thermoset composite materials. The spectrum of a resin was recorded before the cure by embedding the optical fiber in the graphite fiber/polyimide matrix resin prepreg, and then the progress of the cure was monitored during the curing process. This type of remote sampling shows tremendous potential for opening totally new areas of usage for FT-IR spectrometry, including the studies of hazardous materials, enclosed reactions, and processes that do not allow samples to be taken inside the spectrometer.

Infrared evanescent-absorption spectroscopy with chalcogenide glass fibers

“…(8) I is the transmitted intensity in the presence of an absorber, Io is the 100% transmission intensity, c is the concentration of solute, and ec is the Beer's law Vol. % Acetone (b) Fig.…”

In Situ (Autoclave) Cure Monitoring of Composites with IR Transmitting Optical Fibers

“…6. It reveals the characteristic amine (N-H stretching mode) absorptions centered at 3372 cm· 1 and C-H stretching modes (2900 cm 1 ) attributable to CH 3 and CH 2 groups. Fig.…”

“…Recent research has shown that certain infrared (IR) transmitting optical fibers can be used to monitor the chemical changes that occur when a graphite fiber reinforced resin matrix is heated [1][2][3][4]. These changes are monitored as a result of the optical fiber behaving as an in situ multiple internal reflectance (MIR) cell.…”

Integrating optics and micro-fluidic channels using femtosecond laser irradiation

“…However, the use of such materials limits the functionality of the fabricated devices in the optical domain to near-IR wavelengths. Chalcogenide glasses (ChGs) offer high IR transparency, structural flexibility, and the ability to "tune" physical and optical properties through chemical composition and are thus ideal material candidates for integrated devices capable of sensing chemicals and biological toxins which have their spectral fingerprints in the mid-and far-infrared range [5][6]. In this paper, we describe the fabrication of optical elements and micro-channels on an integrated chip-based platform in chalcogenide glass through both lithographic processing and femtosecond laser direct writing.…”