Photoacoustic Fourier Transform Infrared Research Articles

Surface Defects of TPO Injected Foam Parts for Automotive Applications

Abstract Benefits of reduced vehicle weight can have an important environmental impact since there is a 6 to 8% improvement in fuel efficiency for every 10% in weight reduction. In this work, foaming technology is used to produce injection molded TPO parts (thermoplastic olefin compounds) for the automotive industry with a minimum of 20% weight reduction while retaining a glossy surface quality. It was found by Guo et al. (2006, 2007) that the best strategy to raise the surface quality was to decrease the shot size, the cycling time and the temperature of the injected melt. However, the targeted objective of a minimum of 20% weight reduction was not achieved in these preliminary experiments. Therefore, in this work a blend of TPO and maleic anhydride modified polypropylene (PP-g-MA) was used in order to promote TPO foamability and improve the surface quality of injected parts. Under these conditions, we managed to produce injected molded TPO samples with a 24% weight reduction and good surface quality. Moreover, we investigated the effect of PP-g-MA in the TPO system by performing rheological measurements and photoacoustic Fourier transform infrared (PA-FTIR) analysis to characterize the PP-g-MA physico-chemical interactions with TPO.

Development and In Vitro Evaluation of 5-Fluorouracil-Eluting Stents for the Treatment of Colorectal Cancer and Cancer-Related Obstruction

Self-expanding metal stents (SEMSs) are currently the gold standard for the localised management of malignant gastrointestinal (GI) stenosis and/or obstructions. Despite encouraging clinical success, in-stent restenosis caused by tumour growth is a significant challenge. Incorporating chemotherapeutic drugs into GI stents is an emerging strategy to provide localised and sustained release of drugs to intestinal malignant tissues to prevent tumour growth. Therefore, the aim of this work was to develop and evaluate a local GI stent-based delivery system that provides a controlled release of 5-fluorouracil (5FU) over a course of several weeks to months, for the treatment of colorectal cancer and cancer-related stenosis/obstructions. The 5FU-loaded GI stents were fabricated via sequential dip-coating of commercial GI stents with a drug-loaded polyurethane (PU) basecoat and a drug-free poly(ethylene-co-vinyl acetate) (PEVA) topcoat. For comparison, two types of commercial stents were investigated, including bare and silicone (Si) membrane-covered stents. The physicochemical properties of the 5FU-loaded stents were evaluated using photoacoustic Fourier-transform infrared (PA-FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermal analysis. In vitro release studies in biological medium revealed that the 5FU-loaded stents provided a sustained release of drug over the period studied (18 d), and cell viability, cell cycle distribution and apoptosis assays showed that the released 5FU had comparable anticancer activity against human colon cancer cells (HCT-116) to pure 5FU. This study demonstrates that dip-coating is a facile and reliable approach for fabricating drug-eluting stents (DESs) that are promising candidates for the treatment of GI obstructions and/or restenosis.

Influence of Polymer Composition on the Controlled Release of Docetaxel: A Comparison of Non-Degradable Polymer Films for Oesophageal Drug-Eluting Stents.

Following the huge clinical success of drug-eluting vascular stents, there is a significant interest in the development of drug-eluting stents for other applications, such as the treatment of gastrointestinal (GI) cancers. Central to this process is understanding how particular drugs are released from stent coatings, which to a large extent is controlled by drug-polymer interactions. Therefore, in this study we investigated the release of docetaxel (DTX) from a selection of non-degradable polymer films. DTX-polymer films were prepared at various loadings (1, 5 and 10% w/w) using three commercially available polymers including poly(dimethylsiloxane) (PSi), poly (ethylene-co-vinyl acetate) (PEVA) and Chronosil polyurethane (PU). The formulations were characterised using different techniques such as photoacoustic Fourier-transform infrared (PA-FTIR) spectrophotometry, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The effect of DTX on the mechanical properties of the films, in-vitro release, and degradation tests were also assessed. For all polymers and DTX loadings, the drug was found to disperse homogenously without crystallisation within the polymer matrix. While no specific interactions were observed between DTX and PSi or PEVA, hydrogen-bonding appeared to be present between DTX and PU, which resulted in a concentration-dependent decrease in the Young’s moduli of the films due to disruption of inter-polymeric molecular interactions. In addition, the DTX-PU interactions were found to modulate drug release, providing near-linear release over 30 days, which was accompanied by a significant reduction in degradation products. The results indicate that DTX-loaded PU films are excellent candidates for drug-eluting stents for the treatment of oesophageal cancer.

Study of Colombian coals using photoacoustic Fourier transform infrared spectroscopy

Abstract Five of the most important Colombian coals were studied using Photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy. The PA-FTIR spectra were used to obtain structural parameters and to determine the analytical potential of this technique. The molecular structural parameters, CH 2 /CH 3 , f a , H al /H ar , and (R/C) u were correlated with fixed carbon contained in the samples to determine aliphatic hydrogen, H al , and the aromatic hydrogen, H ar in coals studied here. These parameters enabled the determination of aromaticity, f a , which was found to be between 0.66 and 0.98. The aliphatic and aromatic regions were considered between 3005–2760 cm −1 and 912–670 cm −1 , respectively. Finally, using the molecular structural parameters, the grade of maturation (rank) of coal samples studied was determined.

Nanoclay Based Composite Scaffolds for Bone Tissue Engineering Applications

Scaffolds based on chitosan/polygalacturonic acid (ChiPgA) complex containing montmorillonite (MMT) clay modified with 5-aminovaleric acid were prepared using freeze-drying technique. The MMT clay was introduced to improve mechanical properties of the scaffold. The microstructure of the scaffolds containing the modified MMT clay was influenced by the incorporation of nanoclays. The MTT assay also indicated that the number of osteoblast cells in ChiPgA scaffolds containing the modified clay was comparable to ChiPgA scaffolds containing hydroxyapatite known for its osteoconductive properties. Overall, the ChiPgA composite scaffolds were found to be biocompatible. This was also indicated by the scanning electron microscopy images of the ChiPgA composite scaffolds seeded with human osteoblast cells. Photoacoustic–Fourier transform infrared (PA-FTIR) experiments on the ChiPgA composite scaffolds indicated formation of a polyelectrolyte complex between chitosan and polygalacturonic acid. PA-FTIR studies also showed that the MMT clay modified with 5-aminovaleric acid was successfully incorporated in the ChiPgA based scaffolds. Swelling studies on ChiPgA composite scaffolds showed the swelling ability of the scaffolds that indicated that the cells and the nutrients would be able to reach the interior parts of the scaffolds. In addition to this, the ChiPgA scaffolds exhibited porosity greater than 90% as appropriate for scaffolds used in tissue engineering studies. High porosity facilitates the nutrient transport throughout the scaffold and also plays a role in the development of adequate vasculature throughout the scaffold. Compressive mechanical tests on the scaffolds showed that the ChiPgA composite scaffolds had compressive elastic moduli in the range of 4–6 MPa and appear to be affected by the high porosity of the scaffolds. Thus, the ChiPgA composite scaffolds containing MMT clay modified with 5-aminovaleric acid are biocompatible. Also, the ChiPgA scaffolds containing the modified MMT clay appears to satisfy some of the basic requirements of scaffolds for tissue engineering applications.

Fourier Transform Infrared Measurement of Solid-, Liquid-, and Gas-Phase Samples with a Single Photoacoustic Cell

A photoacoustic detector based on the optical cantilever microphone has been built. The detector is capable of measuring solid-, liquid-, and gas-phase samples. Photoacoustic Fourier transform infrared (FT-IR) measurement with three samples in different phases was demonstrated. Example samples were polyethene, sunflower oil, and methane. The sensitivity of the cell was compared to a commercial photoacoustic FT-IR detector. With the standard carbon black sample the cantilever detector gave approximately five times higher signal-to-noise ratio than the reference detector. The sensitivity with methane was also compared to the DTGS detector of the FT-IR instrument corresponding to an absorption path of 6.3 cm. Simulation of the photoacoustic signal showed that a compromise has to be made in the cell design between sensitivity for solid- and gas-phase samples but it is possible to highly enhance the sensitivity for all types of samples by reducing cantilever dimensions.

Synthesis of Nanocrystalline TiO2 Particles and Their Structural Characteristics

Controlled nanosized TiO2 particles of 4–10 nm were synthesized by a simple hydrolysis method followed by calcination at different temperatures. These particles were investigated using X-ray diffraction (XRD), Photoacoustic/Fourier transform infrared (PA/FTIR) spectroscopy, Raman spectroscopy and electron spin resonance (ESR) spectroscopy to understand their structural properties. X-ray diffraction studies confirmed the anatase phase of the particles where as the PA/FTIR revealed the bands around 1,500 and 3,300 cm−1 due to –OH bands. ESR spectroscopic investigations carried out from 5 to 300 K indicated the presence of an ESR line at g = 2.00 emerging from radical species. It is significant to note that the intensity of the ESR line decreased as the particle size increased.

Rapid bacterial identification with medical and security applications

Recent studies at Pacific Northwest National Laboratory (PNNL) using infrared spectroscopy combined with statistical analysis have shown the ability to identify and discriminate vegetative bacteria, bacterial spores and background interferents from one another. Since the anthrax releases in 2001, rapid identification of unknown powders has become a necessity. Bacterial endospores are formed by some Bacillus species as a result of the vegetative bacteria undergoing environmental stress, e.g. a lack of nutrients. Endospores are formed as a survival mechanism and are extremely resistant to heat, cold, sunlight and some chemicals. They become airborne easily and are thus readily dispersed which was demonstrated in the Hart building. Fourier Transform Infrared (FTIR) spectroscopy is one of several rapid analytical methods used for bacterial endospore identification. The most common means of bacterial identification is culturing, but this is a time-consuming process, taking hours to days. It is difficult to rapidly identify potentially harmful bacterial agents in a highly reproducible way. Various analytical methods, including FTIR, Raman, photoacoustic FTIR and Matrix Assisted Laser Desorption/Ionization (MALDI) have been used to identify vegetative bacteria and bacterial endospores. Each has shown certain areas of promise, but each has shortcomings in terms of sensitivity, measurement time or portability. IRmore » spectroscopy has been successfully used to distinguish between the sporulated and vegetative state. [1,2] It has also shown its utility at distinguishing between the spores of different species. [2-4] There are several Bacillus species that occur commonly in nature, so it is important to be able to distinguish between the many different species versus those that present an imminent health threat. The spectra of the different sporulated species are all quite similar, though there are some subtle yet reproducible spectroscopic differences. Thus, a more robust and reliable method is needed for differentiation. Using chemometrics, a classification scheme was developed and performed on samples sporulated in glucose broth. PNNL has demonstrated that vegetative bacteria and endospores have unique infrared (IR) signatures that can be used to identify to the species-, and in some cases, even to the strain-level. We have shown that the IR spectra of spores of different species tend to be quite similar, yet the small but reproducible differences in the spectra allow for a certain degree of differentiation. Further studies have shown that the culture medium can also have an effect on the spectra. For the distinction between vegetative and endospores, we have consistently observed a series of four peaks at 766, 725, 702, and a fairly sharp peak (FWHM 7 cm-1) at 660 cm-1, present only in the endospore spectra.« less

Determination of lignin content in high-yield kraft pulps using photoacoustic rapid scan Fourier transform infrared spectroscopy

The spectra of a number of kraft pulps from Pinus radiata with varying lignin content (Kappa number) were obtained using a rapid scan photoacoustic Fourier transform infrared (PAS-FTIR) spectrometer and a method was developed for the determination of lignin content. A partial-least-squares (PLS) model was established based on spectral data collected at different mirror velocities. The robustness of the model was statistically evaluated. The outcomes indicate that the PLS model can be used to predict Kappa number of kraft pulps with a high degree of accuracy provided that the moving mirror velocity is ⩽0.5 cm/s.

Experimental investigation of interfaces in hydroxyapatite/polyacrylic acid/polycaprolactone composites using photoacoustic FTIR spectroscopy

Molecular interactions in hydroxyapatite (HAP) polymer composites have been studied using photoacoustic spectroscopy. HAP is mineralized by wet precipitation under two conditions: first is in the absence of polyacrylic acid (PAAc) (ex-situ HAP) and second in the presence of PAAc (in-situ HAP). Porous and solid composites of ex-situ and in-situ HAP with polycaprolactone (PCL) have also been made to evaluate their applicability as bone scaffolds. Photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy studies indicate that both in-situ and ex-situ HAP have HPO4 (2-) in their structure, which leads to Ca2+ deficiency. During crystallization of in-situ HAP, PAAc dissociates to form carboxylate ions, which binds to calcium ions and act as suitable site for nucleation for HAP crystallization. PA-FTIR spectra of porous and solid composites indicate that porous composites adsorb more water, which is hydrogen bonded with carbonyl of PCL. Mechanical tests on solid samples indicate that ex-situ HAP/PCL composites have higher elastic modulus than in-situ HAP/PCL composites. However, in case of porous composites, in-situ HAP/PCL composites are found to have higher elastic modulus. In-situ HAP is chemically and structurally different from ex-situ HAP. This modified HAP causes variation in microstructure of porous composite and hence alteration of its load transfer mechanisms and hence mechanical properties.

Photoacoustic FTIR spectroscopic study of undisturbed nacre from red abalone

In this work, photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy has been utilized to study interfacial interactions of undisturbed nacre and nacre powder from red abalone shell. The spectra of both undisturbed nacre and nacre powder showed characteristic bands of aragonite and proteins. Although nacre powder and undisturbed nacre are chemically identical, PA-FTIR spectrum of undisturbed nacre is found to be significantly different from that of nacre powder. A broad and strong band is observed at around 1485 cm −1 in nacre powder. The intensity of this band is notably reduced in undisturbed nacre. This result is explained on the basis of interfacial interactions between aragonite platelets and acidic proteins. It is also observed that band at around 1788 cm −1 originates from three overlapping bands 1797, 1787 and 1778 cm −1. The band at around 1787 cm −1 is assigned to C O stretching of carboxylate groups of acidic proteins. The other two bands at 1797 and 1778 cm −1, originate from aragonite and have been assigned to combination bands, ν 3 + ν 4a and ν 3 + ν 4b, respectively. For the study of stratification in undisturbed nacre, PA-FTIR spectra have been collected in step scan mode. The variation in spectra with depth can be attributed to changes in conformation of proteins as well as interfacial interactions.

The surface modification of nanoporous SiO x thin films with a monofunctional organosilane

The surfaces of nanostructured, porous SiO x /Si (air-oxidized Si) and SiO x thin films, deposited by excimer laser ablation in He and He + O 2 gas ambients, respectively, have been modified by the deposition of a monofunctional organosilane. They were characterized using photoacoustic Fourier-transform infrared (FTIR) X-ray photoelectron (XPS) spectroscopies, and field-emission scanning electron microscopy (FESEM). Photoacoustic FTIR analysis indicates that the organosilane has hydrolyzed to form a silanol, which has chemically reacted with SiO x through its surface silanol ( SiOH) group, to form siloxane (Si O Si) structures. An enhanced IR spectral signal is found, due to the expansion and contraction of both the pores of the solid and the gas within them.

Spectroscopic Evidence for π−π Interaction between Poly(diallyl dimethylammonium) Chloride and Multiwalled Carbon Nanotubes

The interaction between multiwalled carbon nanotubes (MWCNTs) and aqueous poly(diallyl dimethylammonium) chloride (PDDA) was studied by X-ray photoelectron (XPS) and photoacoustic Fourier transform infrared (PA-FTIR) spectroscopies. We have found that the mild sonication of MWCNTs in aqueous PDDA results in a significant improvement of CNT dispersibility and greatly enhances their adhesion to Au and Si substrates. The MWCNT-PDDA interaction is due to the presence of an unsaturated contaminant in the PDDA chain, as confirmed by both XPS and PA-FTIR, which enters into a pi-pi interaction with the CNTs. Electrostatic group repulsions of the coated CNTs then provide the dispersibility and adhesion.

Surface tailoring of an ethylene propylene diene elastomeric terpolymer via plasma‐polymerized coating of tetramethyldisiloxane

AbstractIn the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH3)2SiOSi(CH3)2H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry

Recent advances in stratification and film formation of latex films; attenuated total reflection and step-scan photoacoustic FTIR spectroscopic studies

Surfactant–latex molecular level interactions as well as transient effects during latex film formation play an important role in latex technology. This review article focuses on the siloxane effects on anionic sodium dioctylsulfosuccinate (SDOSS) surfactant exudation during latex coalescence and quantitative analysis of SDOSS distribution at the both film–air (F–A) and film–substrate (F–S) interfaces. Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy was utilized for characterization of the interactions between SDOSS and styrene–butyl acrylate latex copolymers. In addition, studies of SDOSS stratification along with depth-profiling analysis during latex film formation utilizing step-scan photoacoustic (S2-PAS) FTIR spectroscopy illustrate that SDOSS content is enriched at the F–A interface and decreases as the penetration depth increases across the latex film thickness. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1321–1348, 1998

Chemisorption on diamond surfaces studied by vibrational spectroscopies

Hydrogen, oxygen, and halogen chemisorption states on a diamond surface are investigated by three different vibrational spectroscopies; (i) Fourier-transform Infrared (FTIR), (ii) High-resolution Electron Energy Loss Spectroscopy (HREELS), and (iii) Sum-frequency Generation Spectroscopy (SFG). Diffuse reflectance FTIR and Photoacoustic FTIR are effective for use with the powder diamond samples with large surface areas. Diffuse reflectance and photoacoustic FTIR have clarified a lot of the chemisorption structures of hydrogen, oxygen and fluorine chemisorption on powdered polycrystalline diamond surfaces. HREELS is a powerful technique to observe species on single crystal diamond surfaces with small surface areas. HREE-LS has revealed a characteristic feature of hydrogen chemisorption on (100) and (111) diamond surfaces. SFG is a quite new spectroscopic technique using both a frequency fixed visible laser and a frequency tunable infrared laser to study single crystal diamond surfaces, even in a reactive gas environment. In this review, we introduce these three different vibrational spectroscopies as techniques to study diamond surface chemisorption.

Characterization of hydroxyapatite and carbonated apatite by photo acoustic FTIR spectroscopy.

An understanding of the interfacial relationship between a bioceramic implant and the adjacent bone tissue is facilitated by precise characterization of the associated structures. The structure of different commercial synthetic hydroxyapatite powders and a novel carbonated apatite have been studied with photo-acoustic (PAS) Fourier transform infrared (FTIR) spectroscopy. The PAS technique is an ideal method for analysing biomaterials, as materials can be analysed without the need to reduce the particle size or to dilute with KBr. Spectra from carbonated apatite appear to be different from those of commercial hydroxyapatite powders, with the main difference lying in the carbonate and phosphate ratio. Commercial hydroxyapatite powders from different sources have also been analysed and compared.

An Improved Technique for the Determination of Isocyanurate and Isocyanate Conversion by Photoacoustic FTIR

Conventional rigid polyisocyanurate (PUIR) foams blown with HCFC-141b often suffer from poorer compressive strengths, dimensional stability and inferior flammability properties when compared to foams blown with CFC-11. It is often hypothesized that these properties can be improved by increasing the isocyanurate (or "trimer") conversion by means of catalyst optimization and increased isocyanate index. A convenient, yet reliable method for the determination of the amount of isocyanurate in a PUIR foam has been missing in this industry for a long time, though several attempts have been documented in the literature. The purpose of this paper is to introduce an improved isocyanurate conversion test by photoacoustic Fourier Transform Infra Red (FTIR) technique. This involves creating a baseline through three anchor points at approximately 1637 cm−1, 1469 cm−1, and 1349 cm−1. The absorbance of the isocyanurate peak at 1410 cm−1 is taken relative to the absorbance of the phenyl peak at 1602 cm−1. The phenyl peak is preferred to the urethane peak because the absorbance of phenyl groups in a foam is inherent to the amounts of polyols and isocyanates used in the foaming reaction, whereas the urethane linkages in the foam are created by a reaction between the two and are, therefore, variable depending on the extent of the reaction in the presence of catalysts and possibly water. In addition, the relative ratios of the absorbances of isocyanate end groups (at 2277 cm−1) and carbodiimide groups (at 2136 cm−1) to the phenyl groups can also be determined by generating a baseline through the anchor points at approximately 2470 cm−1, 2207 cm−1 and 2000 cm−1. This allows one to gain a better assessment of the overall kinetics of the isocyanate reactions and creates opportunities to improve the isocyanurate conversion through formulation optimization. The method is not limited to polyisocyanurate foams, as isocyanate conversion is an important parameter to follow in polyurethane foams as well, especially in all carbon dioxide blown foams. The method was found to be quite reproducible, and further statistical analysis to ensure the validity of this technique is under way.

Quantitative Characterization of Polymer Structure by Photoacoustic Fourier Transform Infrared Spectroscopy

Photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy is not a widely used analytical technique with only a few quantitative applications to polymers reported. To explore the potential use of PA-FTIR in quantitative polymer analyses the determination of vinyl acetate in EVA, acrylonitrile in NBR, ethylene in EPDM, styrene in SBR, and vinyl-butadiene in SBR were studied. The results indicate that despite the theoretical complexities of PA-FTIR, simple quantitative relationships can be found for many of these polymer analyses.

Chemisorption on Diamond Surfaces studied by Vibrational Spectroscopies

Hydrogen, oxygen, and halogen chemisorption states on a diamond surface are investigated by three different vibrational spectroscopies; (i) Fourier-transform Infrared (FTIR), (ii) High-resolution Electron Energy Loss Spectroscopy (HREELS), and (iii) Sum-frequency Generation Spectroscopy (SFG). Diffuse reflectance FTIR and Photoacoustic FTIR are effective for use with the powder diamond samples with large surface areas. Diffuse reflectance and photoacoustic FTIR have clarified a lot of the chemisorption structures of hydrogen, oxygen and fluorine chemisorption on powdered polycrystalline diamond surfaces. HREELS is a powerful technique to observe species on single crystal diamond surfaces with small surface areas. HREE-LS has revealed a characteristic feature of hydrogen chemisorption on (100) and (111) diamond surfaces. SFG is a quite new spectroscopic technique using both a frequency fixed visible laser and a frequency tunable infrared laser to study single crystal diamond surfaces, even in a reactive gas environment. In this review, we introduce these three different vibrational spectroscopies as techniques to study diamond surface chemisorption.