STEP-SCAN PHOTOACOUSTIC SPECTROSCOPY

FTIR step-scan photoacoustic spectroscopy was used to study the composition of thermoplastic olefin films, as a function of depth below the surface. Experiments were completed at various modulation frequencies, enabling a stratification model to be developed. The uppermost layer (0-3 im) showed large changes in talc and PP concentration, while the layer below showed a significant decrease in both the phases. In the third layer (6-9 pm), all three phases showed the maximum values. In the fourth layer (9-12 pm), the talc concentration reduced, whilst concentrations of elastomeric copolymer of ethylene and propylene (EPR) and PP were observed, decreasing with depth (44). 

Dallas, Tx., Spring 1998, p.20-1. 012 STEP SCAN PHOTOACOUSTIC FT-IR SPECTROSCOPY AND STRATIFICATION PROCESSES IN THERMOPLASTIC OLEFINS (TPO)... 

Vibrational spectroscopy represents two physically different, yet complementary spectroscopic techniques IR and Raman spectroscopy. Although both methods have been utilised for many years, recent advances in electronics, computer technologies and sampling made Fourier transform infrared (FTIR) and Raman (FT-Raman) one of the most powerful and versatile analytical tools. Enhanced sensitivity and surface selectivity allows non-invasive, no-vacuum molecular level analysis of surface and interfaces. Emphasis is placed on recent advances in attenuated total reflectance (ATR), step-scan photoacoustic (SS-PA), Fourier transform infrared (FTIR) and FT-Raman microscopies, as utilised to the analysis of polymeric surfaces and interfaces. A combination of these probes allows detection of molecular level changes responsible for macroscopic changes in three dimensions from various depths. 7 refs. 

Step-scan photoacoustic data are presented that prove the ability of the technique to successfully isolate the infrared signature on the top layer from the infrared spectrum of the bulk material, proving the sub-micron resolution capability of the method. Results are shown that underline the fact that the most serious problem in photoacoustic spectroscopy is saturation at high absorptivities. 12 refs. 

Jurdana LE, Ghiggino KP, Leaver IH, and Cole-Clarke P (1995) Application of FT-IR step-scan photoacoustic phase modulation methods to keratin fibres. Applied Spectroscopy 49 361-366. 

An additional technique that can obtain spatially resolved spectral information is step-scan photoacoustic IR spectroscopy. Spectra can be obtained from different depths of a layered sample quickly and with higher spatial resolution (in some cases less than 1 pm) than the diffraction-limited optics of IR microscopes are capable of obtaining. 

Neubert, R. Collin, B. 8t Wartewig, S., Direct determination of drug content in semisolid formulations using step-scan FT-IR photoacoustic spectroscopy Pharm. Res. 1997, 14, 946-948. 

Further recent developments in DSC and IR techniques, with respect to the study of SC barrier properties, include step-scan FT-IR photoacoustic spectroscopy [195] and combined microscopic differential calorimetry-Four-ier transform infrared (DSC-FTIR) spectroscopy [196]. The former allows depth profiling of the membrane the latter enables the simultaneous detection of calorimetric and structural modifications during a thermal transition. Technological advances in DSC and IR will, no doubt, continue to expand the application of these techniques to the study of skin barrier function. 

Orlando, FL., Fall 1996, p.39-40. 012 HIGH-PRESSURE PHOTOACOUSTIC STEP-SCAN FT-IR SPECTROSCOPY OF POLYMERS Pennington B D Urban M W North Dakota State University (ACS,Div.of Polymeric Materials Science Engng.)... 

No.5, March 1999, p. 1131 -7 POLYMERIZATION OF HYDROXYALKYL METHACRYLATES CHARACTERIZED BY COMBINATION OF FT-RAMAN AND STEP-SCAN FT-LR PHOTOACOUSTIC SPECTROSCOPY... 

Some new developments of two-dimensional spectroscopy are discussed. As a specific example, two-dimensional correlation analysis of a polymer laminate film using several different spectroscopic techniques is presented. The versatility of this technique was developed using depth-profiling photoacoustic spectroscopy, mid-and near-IR dynamic rheooptical developments, and spectroscopic imaging microscopy. Spatial and temporal variations of near-IR spectra are effectively analysed by the two-dimensional correlation technique. Step-scanning FTIR spectrometers provide an opportunity to obtain desired spectral information often difficult to obtain by the conventional rapid-scanning technique. 12 refs. 

Applied Spectroscopy 51,No.8,Aug.l997,p.l238-44 PHASE-RESOLVED DEPTH PROFILING OF THIN-LAYERED PLASMA POLYMER FILMS BY STEP-SCAN FOURIER TRANSFORM INFRARED PHOTOACOUSTIC SPECTROSCOPY... 

Urban [7] studied the quantitative aspects of alternated total reflectance and photoaconstic step-scan FT-IR and interfacial analysis of polymeric films. There are significant implications arising from the ability to stratify polymer surfaces and interfaces using attenuated total reflectance (ATR) and photoacoustic step-scan FT-IR spectroscopy. Theoretical concepts and... 

There are several types of measurements for which standard rapid-scanning interferometers may be inappropriate. These include hyperspectral imaging (Section 14.5), high-speed time-resolved spectrometry (Section 19.2), photoacoustic spectroscopy (Section 20.3), and sample modulation spectroscopy (Chapter 21). For these measurements it is necessary to hold the optical path difference constant while a measurement is made, after which the OPD is rapidly advanced to the next sampling position and then held constant once again for the next measurement. This process is repeated until all the data needed to obtain the interferogram are acquired. Such interferometers are called step-scan interferometers. 

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