Measurements from Polymer Surfaces Using Fourier Transform Infrared Photoacoustic Spectroscopy, Study notes of Chemistry

Download Measurements from Polymer Surfaces Using Fourier Transform Infrared Photoacoustic Spectroscopy and more Study notes Chemistry in PDF only on Docsity! 7 AD-A05 398 MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MATERIA -ETC F/6 11/9 ORIENTATION MEASUREMENTS FROM POLYMER SURFACES USING FOURIER TR--ETC(U) SEP AS K KRISHNAN, S HILL, J P HOBBS NOISIA TA C 0676 UNCLASSIFIED TA-A NL SECURITY CLASSiFICATIcN ow rTP!S P40E !-hnData Untexqi u REPORT~~ ~ ~ DOUETTO PIfjj LOEZ CC .APLETING Fe.4.tI Technical Repor 04 . ~ C. LT\ 4. TITLE (and Subtitle) Orientation S. TYPE OF REPORT & PERIOD COVEREO Measurements from Polymer Surfaces Using Fourier Transform Infrared TechnicalReport Photoacoustic Spectroscopy S. PERFORMING ORG. REPORT NUMBER 7 ?. AUTHOR(*) S. CONTRACT OR GRANT NUMBER(.) C0 K. Krishnan, S. Hill, J.P. Hobbs N00014-78-0676 and C.S.P. Sung W 9. PERFORMING ORGANIZATION NAME AND ADDRESS SO. PROGRAM ELEMZNT. PP,.;C-. TASK AREA & WORK UNIT NUMBERS Department of Materials Science and Engineer ng NR 356-699 (472) 1M.I.T., Cambridge, !'--k 02139 il. CONTROLLING OFFICE NAM. AND ADDRESS 12. REPORT DATEN I OSeptember 1981 Office of Naval Research 1. NUMBER OF PAGES 800 N. Quincy St., Arlington, VA 22217 14. MONITORING AGENCY NAME a ADCRES(iI diffetnt irom Controlling OfEice) 15. SECURITY CLASS. (of this :p;rt) unclassified DISa. ECL/.SSIFiCAT Oh,'DO N0'0AN SCHEDULE 16. DISTHIRUTION SrATEM NT (of ".e Report) Approved for public release; distribution unlimited 17. DISTrt BUT [ON ST AT EMjENt (of the atetract entereed in Slock 20, I diffIerent from Repot) LCa i-TEol OCT 1 31981 IS. SLFPLE-l1'-. ARY NOTES Prepared for publication in journal. - 19. KEY WOrC.". (Cr,tinue cn reverse sido if necessa.ry mid Identify by block nun::er) Orientation Fourier Transform Ir. Spectro*,cc>:'" Photoacoustic Spectroscopy Polymer Surface IR internal reflection dichroism Polyethylene tereDhthalate 20. A S' rAC' Cntl.-iwe -n r - te s f If nece.8.s-Y Ve1d i',ntify tw block .mber) 'Fourier Trans[orr. iRPhtoacoustic (FTIR-PS) diclroisn. studies h 1ve e-1- applied to determinc moleuhlar orientation irom the surface of. o:e-,.-v drawn poly(eth.lcne torephth:lato) film. :--hen comilared with AT c d- ;roc spectra obtained with a modified, rotatble sample ho-ier on t, sone pp. sample, PA snectra sho: saituiration elfects in strong absorrtion bands near 1730, 1250 and 1100 cu"; prcalv due to the grcatcr '.,crott, ' , depth in the PA teci.niqte. The dichrioc ratios(-y/. ) on the p hnc of DD , FR! 1473 EDITIO o NV' O. . "1 . , SECURIT CLASSII(. N 7 -L.1 A C '.. .. .2 81 I0 1... Abstract Fourier Transform IR Photoacoustic (FTIR-PAS) dichroism studies have been applied to determine molecular orientation from the surface of one-way drawn poly(ethylene terephthalate) film. When compared with ATR dichroic spectra obtained with a modified, rotatable sample holder on the same sample, PA spectra show saturation effects in strong absorption bands -I near 1730, 1250 and 1100 cm , probably due to the greater penetration depth in the PA technique. The dichroic ratios (k x/k y) on the plane of the sample film have been calculated from PA spectra, only on bands which do not show saturation and compared with the analogous ratios determined from ATR dichroic spectra. For three well-known parallel bands at 1335, 975 and -I 795 cm the dichroic ratio is greater than unity in both ATR and PAS, as expected from the drawing process. In general, somewhat lower dichroic ratios are observed by PA spectra than by ATR spectra with this sample. Possible reasons for this trend are discussed. This study demonstrates the potential of FTIR-PAS dichroism as a complementary technique to ATR dichroism, especially on samples with rough or brittle surfaces. Aceession For NTIS GRA&I DTIC TAB Unannounced r] Justification By- Distri,,ltion/ .Avaiibility Codes- Avail t!j,or Dist pcij Liz Photoacoustic spectroscopy (PAS) has been shown to be a very useful experimental technique for the study of the spectra of gases, liquids, and solids. Rosencwaig(l) has recently reviewed the theoretical and experimental aspects of PAS and has shown its applicability especially for the study of solids. In the PAS experiments the solid under study is placed in a sealed cell containing an inert gas and a highly sensitive microphone. Pulsed or chopped radiation is focussed on the sample by means of suitable optics. If the sample absorbs radiation at any particular fre- quency, the absorbed radiation is converted into thermal energy by non- radiative processes. This thermal energy is transmitted to the surrounding gas and sets up a pressure wave in the cell. This pressure or acoustic wave is detected by the microphone resulting in the PA signal. This signal is proportional to the incident energy, and is also dependent on the thermal and optical properties of the sample. The thickness or the depth of the sample from which the PA signal emanates is also dependent on the chopping frequency. Rosencwaig(l) has shown that this depth can be of the order of 10 to 100 micrometers at low (15 KHz) chopping frequencies and of the order of 0.1 to I micrometer for high (1600 KHz) chopping frequencies. The PA technique has been recently extended to the mid-infrared region of the electromagnetic spectrum by several investigators using dispersive(2) or Fourier transfor-m(3,4) spectrometers. Krishnan(5) has shown that under normal operating conditions of the Fourier transform infrared (FT-IR) instru- ments, the PA signal can arise from a layer of thickness around 10 micrometers for typical polymers at 1000 cm . This thickness would then represent an intermediate case when compared to infrared surface measurement techniques such as attenuated total internal reflectance (ATR) and bulk measurement 2 ... . . | - - _______ n | • i | i____| | techniques such as transmission. One of us (Sung,6) has recently shown that the dichroic ratios and hence the surface orientation of polymers could be studied using a modified polarized IR-ATR technique. In this note we show that good quality dichroic spectra can be obtained for polymers using the PA method. The results obtained from PA spectra will be compared with the dichroic ratios obtained for the same sample by the modified polarized ATR technique. The sample used in the present study was a sheet of poly(ethy- lene terephthalate), one-way drawn between a pair of rollers. The surface studied was that facing the hot roller. All the spectra presented here were-II recorded at 4 cm 1 spectral resolution using a Digilab FTS-15 Fourier trans- form infrared spectrometer. The polarized ATR spectra were recorded using a specially designed accessory with a symmetrical KRS-5 crystal, as described in Reference 6, and a liquid nitrogen cooled mercury cadmium telluride detec- tor. The polarizer in the ATR accessory (a germanium double diamond crossed- plate type from Harrick) was set at perpendicular polarization (TE wave), and two spectra were recorded for the sample oriented with its draw axis perpendicular and parallel to the incident plane. The ratio of peak heights in the two spectra will then yield the dichroic ratio kx/ky, where x is the stretch direction and y is transverse to x. The PA spectra were recorded I using a Digilab PAS cell and a gold wire grid polarizer (Perkin-Elmer). Two PAS spectra were recorded, this time by keeping the sample orientation con- stant but by changing the polarizer orientation by 90 degrees. The ratio of the peak heights in these two spectra will also yield the dichroic ratio k /k x y Figure I shows the k. spectra from the PA (top) and the ATR (bottom) measurements. One can see the qualitative similarity in the appearance of the two spectra. Figure 2 shows the corresponding kv spectra. -- 3 References 1. Rosencwaig, A.; "Photoacoustics and Photoacoustic Spectroscopy", John Wiley and Sons: New York, 1980. 2. Low, I.I.J.D.; Parodi, G.A. Infrared Physics 1980, 20, 333; Appl. Spect. 1979, 34, 76. 3. Rockley, M~.G. Chem. Phys. Lett.- 1979, 68, 455; 1980, 75, 370; Appi. Spect. 1980, 34, 405. 4. Vidrine, D.W. Appi. Spect. 1980. 34, 314. 5. Krishnan, K. Appl. Spect. 1981 (in press). 6. C.S.P. Sung Macromolecules 1981, 14, 591. 7. Jasse, B.; Koenig, J.L. 3. Macromol. Chem. 1979, C17(1), 61. 6 - . Acknowledgement This work was in part supported by the Office of Naval Research. We also acknowledge the generosity of Digilab, who made an FTS-15 available for our ATR dichroism studies. We thank Dr. Willis of ICI (England) for providing the sample PET film used in this study. I7 Table 1. Comparison of Dichroic Ratio (k 1 k ) on the PET Surface by FTIR-ATR and FTIR-PAS Techniques Bands- Dichroic, Ratio (ke-1k.) (cC 1) ATR PAS 1335 6.08 2.56 975 4.09 2.78 795 1.73 1.39 PHOTOACOUSTIC SIGNAL ATR ABSORBANCE | NM, eto 6S i) 14a Zee ae ee WAVENADERS, PEt, oursioe RESz4 OP Figure 2 sP472-3/B5 472:GAN: 716:enj 78u 472-608 TEC~ELICAL .EORT DISR:3Ur-iON LIST, 356A No. No. Covies Cooies Dr. Stephen H. Carr Picatinny Arsenal Department of Materials Science Attn: A. M. Anzalone, Building 3401 Northwestern University SMfUPA-FR-M-D Evanston, Illinois 60201 1 Dover, New Jersey 07801 Dr. M. Broadhurst Dr. J. K. 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