Young Shin Kim, University of Delaware, Newark, DE, Christopher M. Snively, University of Delaware, Newark, DE, D. Bruce Chase, DuPont Experimental Station, Wilmington, DE, and John F. Rabolt, University of Delaware, Newark, DE.
Although the previously developed technique of planar array infrared (PA-IR) spectroscopy offers a number of advantages over Fourier transform infrared (FT-IR) methods such as ultrafast speed (<100 µsec) and excellent sensitivity, obtaining a spectrum of films in the range of 1800-1000 cm-1 on a water subphase of a Langmuir trough remains difficult. This is due to the poor IR reflectivity of water, the extremely low concentration of the thin film on the surface, and the interference of water bands. In this study, we report a new planar array infrared reflection spectrograph (PA-IRRS), which has several advantages over conventional approaches. By splitting the incident infrared beam into two sections on a plane mirror or a water trough, instead of at the front of the globar source, the performance of this instrument is shown to be comparable to that of the dual-beam instrument although this instrumental setup is the same with that of the single-beam instrument. Due to this design, the instrument accommodated large infrared accessories, such as the water trough, without a loss of infrared beam intensity. Using this instrument water vapor could be subtracted out and was obtained a high quality spectrum for a poly(L-lactic acid) Langmuir film on the water subphase, with a resolution of about 8 cm-1, in 10.8 sec. Hence, this PA-IRRS system has great potential for investigating the time-resolved dynamics of a broad range of Langmuir films, such as cellular membranes or biopolymers, on the water subphase.