The destruction-free analysis of polymers by fourier transform infrared photoacoustic and fourier transform Raman spectroscopy: A comparison

With the introduction of rapid–scanning Fourier transform infrared (FTIR) and recently Raman (FT–Raman) spectroscopy, vibrational spectroscopy has been launched into a new era of applications in polymer chemistry and physics. Thus, the increase in sensitivity provided by multiple scanning has led to the breakthrough of new, destruction–free sampling techniques, such as photoacoustic and Raman spectroscopy. This paper provides a comparison between data produced by FTIR photoacoustic and FT–Raman analysis of a range of polymers, and structural information available from both techniques is discussed.     

Analysis of orientational relaxation in binary blends of long and short polystyrene chains by fourier transform infrared dichroism and small-angle neutron scattering

Measurements of the local orientational order and average chain anisotropy in non-uniform polystyrene are reported. Fourier-transform infrared dichroism spectroscopy has been used to determine the effects of short deuterated chains (Mw = 500 to 188 000) on the orientational relaxation of long entangled chains (Mw = 2 000 000) in bidisperse melts uniaxially deformed above the glass transition temperature. While the long-chain relaxation is found to be dependent on the short-chain concentration, the local orientational order of the latter is molecular weight dependent consistent with the classical relaxation theories. The FTIR experiments are also combined with small-angle neutron scattering measurements which probe the deuterated-chain anisotropy in the defomed melts. There is evidence, from the combination of the two techniques, that although the short chains possess a negligible local orientational order, there exists an important anisotopy in the short chain distribution in space.     

Polarization fourier transform infrared spectroscopy

Some Fourier transform infrared spectroscopic studies with linearly and circularly polarized radiation are reported. They were all carried out by means of the differential technique, consisting in the comparison of two single-channel spectra of opposite polarization. Thus, linear dichroic or circular dichroic spectra with positive and negative bands were recorded. Typical application examples of both techniques are presented.     

Far infrared fourier transform spectroscopy of semiconductors

Fourier transform spectroscopy (FTS) is one of the most important tools in the study of shallow level donors and acceptors in semiconductors. When combined with a two-step photothermal ionization process detected photoconductively, FTS allows measurement of optical transitions of donor-bound electrons (and acceptor-bound holes) in ultra-pure germanium samples with impurity concentrations <10⁹ cm^–3 (i.e. one electrically active impurity in 4×10¹³ host atoms). The experimental high resolution study of the hydrogen-like excited state series of shallow levels has yielded as many as 19 lines of width as small as 10eV for some centers. These results have stimulated theoretical work which has led to the unambiguous assignment of quantum states to many bound excited states. Extensive studies of ultra-pure Ge crystals grown under different well-controlled conditions have led to the discovery of a large number of novel shallow impurity complexes. Study of the multiplicities and symmetries of the associated electronic states has led to a detailed understanding of the unusual static and dynamic structures of these novel centers. The chemical composition has been deduced from correlations between the concentration of a particular center and the materials involved in crystal gowth. Isotopic substitution of hydrogen with deuterium has led to the unambiguous proof of the presence of hydrogen in several of the novel centers. In addition to the high resolution spectra of shallow electronic levels, vibrational spectra of bond-centered interstitial oxygen in ultra-pure Ge are noteworthy for their extraordinarily sharp lines.     

Mammalian cell growth studiedin situ by fourier transform infrared spectroscopy

Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology.     

Fourier transform infrared study of orientation and relaxation in poly(methyl methacrylate)

Infrared measurements of the dicroic ratio of poly-(methyl methacrylate) absorption bands provide a valuable method for determining the orientation as well as the relaxation of chains during stretching. Different strain rates and temperatures of stretching were used. Orientation relaxation was determined and a master curve was obtained at a reference temperature T_O = 135°C. The master curve shows that orientation relaxation behaves similarly to mechanical relaxation.     

板蓝根颗粒中蔗糖含量的红外光谱法测定

A method for rapid quantitative determination of sucrose in isatis-root granules by Fourier Transform Infrared Spectrophotometry(FTIR) was developed. Potassium ferricyanide was chosen as an inside mark material because it has only one strong absorption peak at 2117cm-1 and the peak was chosen as its quantitative peak. The peak at 1283cm-1 is the characteristic absorption of sucrose and was chosen as the quantitative peak of sucrose. The ratio of the two absorbances is I=Ai/As.K3[Fe(CN)6] and sucrose were mixed according to a certain mass ratio m=mi/ms to prepare standard samples. The curve of m versus I is the quantitative working curve. The linear range for sucrose is 5.0～23.0mg/g,the recovery is in the range of 91%～103%,the relative standard deviation is less than 5%.     

Polychlorobiphenyls differentiation and identification by gas chromatography/fourier transform infrared spectroscopy

Reference infrared vapour phase spectra of 20 polychlorobiphenyls (PCBs) have been obtained by gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR). These spectra are consistent with those of PCB obtained by diffuse reflectance IR spectroscopy (DRIFT) and with those of more simple molecular structures (iodochlorobenzenes, 1-bromodichlorobenzenes). The IR frequencies of the GC/FTIR spectra of PCB are assigned in terms of substitution patterns. This work shows that GC/FTIR can be a good approach for differentiation and identification of PCB in complex mixtures.     

Fourier transform raman spectroscopy using a bench-top fourier transform infrared spectrometer

The use of a bench top FTIR spectrometer for near infrared Fourier transform Raman spectroscopy is demonstrated. The use of near infrared excitation results in fluorescence free Raman spectra allowing previously difficult samples to be measured.     

Segmental orientation and mobility of ferroelectric liquid crystal polymers

IR spectroscopy was used to study the orientation and mobility of different molecular segments in a side chain ferroelectric liquid crystalline polymer (FLCP) in the book-shelf geometry. It was directly shown that the tilt angles for the mesogenic units and the spacers are different. The data obtained allowed us to construct a detailed model of segmental orientation in the SC phase for this FLCP. This model is consistent with the 'zigzag' model for tilted smectic phases. The rotational bias of carbonyl bonds is also confirmed and a possible orientation function for the carbonyl group is discussed. Time-resolved step-scan FTIR spectroscopy enabled us to follow the intra- and inter-molecular response of the FLCP to an external electric field with a time resolution of 5 mus. It was detected that mesogenic moiety, spacer and backbone take part in the reorientation process. The time responses of different molecular segments are similar on the time scale of a few hundred microseconds.     

Segmental versus chain dynamics of linear polymers

Segmental dynamics of relatively short linear polymers are discussed in terms of two distinct contributions, one related to the local segmental motion (alpha relaxation) and the other to polymer-specific effects that reflect Brownian dynamics of the polymer under chain connectivity constraints (Rouse relaxation modes). These two aspects of polymer dynamics are reflected, though differently, in relaxation spectra of different experimental techniques. Two contrasting cases of the (collective) dipolar response (dielectric techniques) versus the individual segmental response (e.g., NMR spin-lattice relaxation spectroscopy) are considered. The second-rank orientational correlation function of an elementary (Kuhn) segment, directly related to NMR observables, is derived in terms of Rouse normal modes. The effect of alpha dynamics is estimated under the assumption of a separation of time scales which, as it is argued, is a necessary precondition of the Rouse approach. The relative magnitude of the polymer-related dynamics is expressed through the number of elementary Rouse units in the chain and the number of Kuhn segments in a Rouse unit. The results are discussed in the context of recent literature.     

Conditions of measurement of infrared absorption band intensities by fourier transform spectrometry

The influence of infrared spectra of some different conditions required in the use of modern FTIR spectrometers has been studied. This work has been performed in two ways: firstly, the influence of factors such as apodization function, level of zero filling, number of data points and phase correction procedure is determined from experimental data, and, secondly, numerical simulation of the whole process has been carried out in order to separate experimental error from that deu to the mathematical treatment.     

Molecular orientation of rigid‐rod polyimide films characterized by polarized attenuated total reflection/fourier transform infrared spectroscopy

The variations in the molecular orientation of uniaxially drawn rigid‐rod polyimide films were systematically characterized in all three dimensions with polarized attenuated total reflection/Fourier transform infrared spectroscopy. The second‐order orientation coefficients were directly deduced from the anisotropy in IR absorptions of particular bands. With the draw ratio increasing, the state of the molecular orientation changed from being nearly planar to completely uniaxial via biaxial orientation, and the degree of orientation was much larger than that of a semirigid polyimide having an ether linkage at the same draw ratio, which originated from the rigid‐rod structure. In addition, the imide planes were rotationally oriented to the out‐of‐plane direction of the film geometry. Furthermore, the relationship between the molecular chain orientation and the in‐plane birefringence in the biaxial orientation state was examined. The intrinsic birefringence was estimated from biaxial orientation films to be 0.33 at a wavelength of 1307 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 418–428, 2003     

Determination of sucrose by flow injection analysis with fourier transform infrared detection

A new methodology for the determination of sucrose in complex aqueous matrices by flow injection analysis with FTIR detection is presented. The methodology based on the enzymatic hydrolytic cleavage of sucrose by means of invertase to -D-glucose and -D-fructose. A special manifold consisting of two internally coupled injection valves being switched simultaneously is applied to facilitate recording FTIR spectra of the sample before and after the enzymatic reaction. The analytical readout is taken from the resulting difference spectrum obtained by subtracting the FTIR spectra of the sample before and after the reaction. The developed methodology uses a GC-IR software to continuously record the FTIR spectra of the effluent from the manifold. The proposed method gives linear results in the range of 10 to 100 mmol/l and has been successfully applied to the analysis of sucrose in synthetic mixtures as well as in real samples such as soft drinks.     

Near infrared fourier transform Raman spectroscopy of human artery

We report the first near IR FT-Raman spectroscopy of normal diseased human artery. In normal human aorta, two bands at 1669 cm⁻¹ and 1452 cm⁻¹ dominate the spectrum and can be assigned to protein amide I and C-H in-plane bending vibrations, respectively. Weaker bands are also observed between 1250 and 1350 cm⁻¹. Non-calcified atherosclerotic lesions with a large amount of necrotic debris below the tissue surface show a relative increase in the intensity of the 1452 cm⁻¹ band. In atherosclerotic aortas which contain calcified deposits several hundred microns below the tissue surface, a strong 961 cm⁻¹ band is observed due to the symmetric stretch of phosphate groups in the calcified salts. The results show that this method provides the capability to probe biological substituents several hundred microns below the tissue surface.     

涂石蜡大米傅立叶变换红外吸收光谱识别分析

针对11种未涂石蜡大米和18个涂不同量石蜡的大米样品,以石油醚提取的油脂为试样,采用傅立叶变换红外光谱仪,扫描样品的傅立叶变换红外吸收光谱,并对光谱进行预处理,提取红外特征信息,将2855与1746、1462与1163 cm-1处特征峰的面积比值为坐标,采用Origín 6.0软件作识别分类图.结果表明:特征峰的面积比值与所涂石蜡量成线性变化,大米油脂的特征峰面积比值在一定的区域分布,涂以0.05%以上石蜡的大米,其油脂特征峰面积比值与未涂石蜡米油脂的值有一定区别.     

Simultaneous measurements of stress and infrared dichroism on polymers

Summary A method for simultaneous measurements of stress and infrared dichroism as time-dependent behavior of polymer films was devised by using a double beam infrared spectrometer. The film sample held between clamps of a stretching device was placed just in front of the entrance slit of the spectrometer where the sample and reference beams came alternately. Two polarizers were used, one in the sample beam and the other in the reference beam. Thus the sample and reference beams were polarized to have the electric vectors parallel and perpendicular to the stretching direction of the sample, respectively. With this arrangement the spectrometer responded only to the difference in the transmittance of the two beams. Setting the spectrometer at one of the wavenumbers of the absorption band maxima, we could record continuously the change in its dichroism during mechanical treatments which gave rise to the molecular orientation in the sample. The stress was recorded automatically by means of a couple of strain gages pasted on the cantilever beam of the stretching device.By theoretical considerations, a simple relationship was found to exist between the quantity recorded on the spectrometer by this method and the orientation function of transition moment of a vibrational absorption band with respect to the stretching direction.The method was applied to the stress relaxation experiments of vulcanized natural rubber carried out at different elongations less than 600% and at the room temperature. Changes of infrared dichroism were measured for five absorption bands at 1664, 1380, 1361, 1129, and 844 cm^–1, of which the last one is a crystalline band. From the results of this study, it was concluded that the stress relaxation observed was ascribed mainly to the amorphous orientation rather than to the crystalline orientation, which was completed almost immediately after elongation.

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Zusammenfassung Eine Methode für gleichzeitige Messungen von Spannungs-und Infrarot-Dichroismus von Polymerenfolien in AbhÄngigkeit von der Zeit wurde unter Verwendung eines Zweistrahlen-Infrarotspektrometers entwickelt. Die Filmproben, zwischen Klemmen in einer Verstreckungsanordnung gehalten, sind am Ort des Eintrittsspaltes des Spektrometers justiert, an dem der die Probe durchlaufende und der Referenzstrahl alternierend eintreten. Zwei Polarisationen, eine im Probestrahl, die andere im Referenzstrahl, wurden verwendet. So sind der Probe-und Referenzstrahl mit dem elektrischen Vektor parallel bzw. senkrecht zur Streckrichtung der Probe polarisiert. Mit dieser Anordnung am Spektrometer wird nur die Differenz der DurchlÄssigkeit der Probe für beide Strahlen gemessen. Wenn man das Spektrometer auf die Wellenzahl eines Absorptionsmaximums der Probe einstellt, lÄ\t sich also kontinuierlich unmittelbar die Änderung des Dichroismus wÄhrend der mechanischen Verformung verfolgen, die aus molekularer Orientierung in der Probe resultiert. Die Spannung wurde automatisch mit Hilfe von Verlagerungsaufnehmern aufgezeichnet.Theoretische Betrachtungen lassen eine einfache Beziehung zwischen den Spektrometerkurven und der Orientierungsfunktion für die verschiedenen Absorptionsbanden in Bezug auf die Streckrichtung finden.Die Methode wurde auf Spannungsrelaxation in vulkanisiertem Naturkautschuk für verschiedene Strekkungen kleiner als 600% bei Raumtemperatur angewendet. Die Messungen der Änderung des InfrarotDichroismus fanden für die 5 Absorptionsbanden bei 1664, 1380, 1361, 1129 und 844 cm^–1 statt, wobei die letztere eine kristalline Bande ist. Aus den Ergebnissen wird geschlossen, da\ die beobachtete Spannungsrelaxation in der Hauptsache Orientierung im Amorphen und nicht einer Kristallit-Orientierung zuzuordnen ist. Letztere ist offensichtlich schon unmittelbar nach der Streckung fast vollstÄndig ausgebildet.

     

Simultaneous measurements of stress and infrared dichroism on polymers

Summary In order to obtain informations on the molecular nature and mechanism of rheological processes on polymers, simultaneous measurements of stress and infrared dichroism were made of polychloroprene (Neoprene Type AC) films during the course of continuous elongation at the constant rate 25%/min and of stress relaxation at 400% elongation. The time dependence of the infrared dichroism was obtained by measuring the intensity change at fixed wavenumbers of absorption band maxima on the differential polarized infrared spectra. Both the degree of crystallinity of sample films and the orientation function of transition moments were calculated from the results of the infrared dichroic measurements under the assumption of uniaxial orientation, which was confirmed to be the case by X-ray diffraction and birefringence measurements.In the continuous elongation experiments, it was found that the orientation functions for crystalline-sensitive bands showed maxima at 25% elongation and then decreased rapidly, changing their signs from positive to negative. There also appeared the yield point in the stress-strain curve and the beginning of sharp decrease of crystallinity at the same degree of elongation 25%. These facts were interpreted in terms of the orientation of the crystalline phase followed by the degradation of crystallites and drawing out of the molecular chain from the crystallites. In the stress relaxation experiments, moderate changes in the orientation functions were found for various characteristic absorption bands. Little difference was observed between changes in the orientation functions for the amorphous and crystalline-sensitive bands. This makes a contrast with the previous results for vulcanized natural rubber, where the orientation of the crystalline phase was completed almost immediately after elongation, while in the amorphous phase the molecular chains were oriented gradually during the course of stress relaxation.

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Zusammenfassung Um Informationen über die molekulare Natur und den Mechanismus rheologischer Prozesse von Polymeren zu erhalten, wurden gleichzeitige Messungen der Spannung und des Infrarot-Dichroismus an Polychloropren-Filmen (Typ AC-Neopren) während der kontinuierlichen Verstreckung bei konstanter Verstreckungsgeschwindigkeit von 25%/min und während der Spannungsrelaxation bei 400% Verlängerung durchgeführt. Die Zeitabhängigkeit des Infrarot-Dichroismus wurde aus der Intensitätsänderung im festen Wellenzahlbandmaximum eines Kristallisationsbandes mit einem differenz-polarisierten Infrarot-Spektrographen festgestellt. Beide, der Kristallanteil der Probe und die Orientierungsfunktion für die Übergangsmomente lassen sich aus den Resultaten unter Annahme einachsiger Orientierung auswerten. Letztere, die einachsige Orientierung, wurde mit Röntgenbeugung und Doppelbrechung sichergestellt.In den Experimenten mit kontinuierlicher Verlängerung zeigten die Orientierungsfunktionen der Kristallempfindlichen Banden bei 25% Verlängerung ein Maximum. Danach sanken sie rasch unter Wechsel ihres Vorzeichens von positiv nach negativ ab. Der Fließpunkt in der Spannungs-Dehnungs-Kurve und der Beginn des scharfen Abfalls der Kristallinität zeigen sich vom gleichen Verlängerungsgrad 25% ab.Diese Tatsachen werden aufgrund der Orientierung der kristallinen Phase erklärt, gefolgt von einem Abbau der Kristallite und einem Herausziehen der Molekülketten aus den Kristalliten. In den Spannungsrelaxationsversuchen wurden gewisse Änderungen der Orientierungsfunktionen für die verschiedenen charakteristischen Absorptionsbanden gefunden. Es ergaben sich geringe Differenzen in der Änderung der Orientierungsfunktionen für die amorphen und kristallempfindlichen Banden. Das steht im Gegensatz zu früheren Resultaten an vulkanisiertem Naturkautschuk. Bei letzteren war die Orientierung der Kristallphase beinahe unmittelbar nach der Dehnung vollständig, während in der amorphen Phase die molekularen Ketten nach und nach im Laufe der Spannungsrelaxation orientiert wurden.

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With 8 figures in 9 details and 1 table     

Application of fourier transform infrared spectroscopy to the study of semicrystalline polymers: Poly(ethylene terephthalate)

An infrared absorbance subtraction technique has been used to “isolate” bands in the composite spectrum of semicrystalline polymers according to their crystalline or amorphous character. Amorphous and crystalline spectra for annealed, melt-quenched, and solution-cast poly(ethylene terephthalate) have been separated. The spectra of the amorphous component show an increased intensity of bands associated with the trans configuration of oxygen about the C? C bond when the polymer is annealed. This increased “trans” band intensity reflects the increased proportion of trans structures as a result of annealing. The amorphous trans bands are shifted approximately 1–3 cm^?1 from their positions in the crystalline “trans” spectrum. The frequency shift of these bands can be attributed to the differences in chain interactions that exist in the amorphous phase and the crystalline lattice. We have also found that under identical anealing conditions the amorphous phase of the melt-quenched polymer contains an increased intensity of conformational trans bands compared to the sample cast from solution.