Step-Scan FT-IR Photoacoustic Spectroscopy: The Signal Phase

Abstract

The model of Rosencwaig and Gersho for the photoacoustic effect is tested. The use of carbon black samples as a phase reference to estimate the apparatus phase φapp from the experimental signal phase φexp turned out to be ambiguous. A new method is presented to correct the experimental signal phases φexp of polymer films for the apparatus phase φapp. The photoacoustic signal phase of some well-defined poly(ethyleneterephthalate) (PET) films is obtained. As a phase reference, transparent thermally thick polymer films were found to be more convenient and dependable than carbon black samples. The resulting phase spectra of thermally thick and thermally thin PET films confirm the Rosencwaig–Gersho theory.

Fourier transform infrared photoacoustic spectroscopy of polymeric laminates

“…As a result of the great experimental PA phase range of the double layer (⌬Ϸ80°), one has to rotate the reference phase coordinates to obtain both the In and Qu interferogram ͑still including app ͒ in the first quadrant of the phase diagram, as discussed earlier. 15 Additionally, we shifted the whole phase spectrum to set transparent ͑in the region between 1550 and 1650 cm Ϫ1 ͒ to 110°, as obtained from the simulations ͑Table IV͒.…”

“…͑For a single-layer system this was done for the CϭO absorption peak of PET. 15 ͒ For ⍜/a g , the full Eq. ͑2͒ was used without simplification or approximation.…”

“…A new method to correct for the apparatus phase-lag app was proposed using the thermally thick and optically transparent limit of the RG theory. 15 Here we present a photoacoustic study on three different polymer double layers. Experimental PA magnitudes and PA phases of the chemically homogeneous double layer of polyethyleneterephthalate on polyethyleneterephthalate ͑PET/ PET͒ and the chemically heterogeneous double layers of polypropylene on polyethyleneterephthalate ͑PP/PET͒ and polyethyleneterephthalate on polypropylene ͑PET/PP͒ are compared with the theory.…”

Application of infrared photoacoustic spectroscopy in catalysis

“…Some of them contain general content of the use and application of FT-IR/PAS [22][23][24][25][26][27][28][29][30][31], others are more specific and are devoted to real-time PA parallel detection of products from catalyst libraries [32], step-scan and depth profiling analysis [33][34][35][36][37][38][39][40], the effect of particle size on FT-IR/PAS spectra [41][42][43][44], the temperature effect on PA signal [45], sample emission effects [46], and synchrotron IR/PAS [47]. During a PA measurement the sample is enclosed in a small, tightly closed sample compartment called PA cell [48][49][50][51][52][53][54].…”

Phase References and Cell Effects in Photoacoustic Spectroscopy

“…Carbon-black-lled rubbers containing various amounts of carbon black are the most comm on phase references, [5][6][7][8]10 but carbon-black powder, 11,12 and a carbon-black-coated membrane 13 have also been used. Wahls et al 14 avoided possible ambiguities with a strongly absorbing reference by using transparent regions of polymers as references. Others dispensed with a separate reference m aterial by assigning 08 to the phase that maximizes the signal, 9,15 and still others did without any reference at all, using an arbitrary scale and relying on the reproducibility of their instrument and procedure.…”