Transmission Fourier Transform Infrared Spectra Research Articles

Cuticle chemistry of the Cheirolepidiaceae Frenelopsis teixeirae from the Lower Cretaceous of Portugal. A case of study using ATR-FTIR spectroscopy

A Cheirolepidiaceae Frenelopsis teixeirae from the Lower Cretaceous of the Santa Susana Formation, near Torres Vedras locality (Estremadura region, western Portugal), is analyzed by means of Fourier Transform Infrared (FTIR) spectroscopy in Attenuated Total Reflection (ATR) mode at both micro and macro scales. This analytical technique (ATR-FTIR spectroscopy), which requires minimal sample preparation and a small amount of material, is used to evaluate the chemical composition of the F. teixeirae cuticles. For this, functional groups (i.e., specific groupings of atoms within molecules), that compose the complex chemical structure making up the F. teixeirae cuticles, are detected, analyzed, and interpreted from the resulting spectra. The Frenelopsis material comprises compressions of eighteen leafy axes with very well-preserved cuticles. Previously reported chemical information derived from transmission FTIR spectra of the foliar cuticle of the podocarp Squamastrobus tigrensis from the Lower Cretaceous of Argentina is used for comparison in order to assess the existence of a distinctive spectroscopic pattern for this Portuguese taxon. Semi-quantitative data derived from FTIR spectra of both fossil taxa were statistically analyzed using principal component analysis (PCA). The F. teixeirae cuticles have a lower contribution of C=O stretch and a lower degree of biopolymeric matrix cross-linking (higher CHal/C=O ratio) than those of S. tigrensis. Despite the existing differences between both conifers, spectroscopic patterns characterizing each fossil taxon are not fully distinctive from a chemotaxonomic perspective. This is mainly related to the relatively variable morphological cuticular features (e.g., trichomes) and to the biomacropolymeric chemistry among the leaves of each fossil taxon.

Serum infrared spectral profile is predictive of the degree of hepatic fibrosis in chronic hepatitis C patients

Assessment of liver fibrosis is crucial to guide the therapeutic strategy in patients with chronic liver disease. We investigated the potential of serum Fourier transform infrared (FTIR) spectroscopy for assessing the degree of hepatic fibrosis in patients with chronic hepatitis C (CHC). The study was conducted on dried serum samples from 94 CHC patients at different histological stages of hepatic fibrosis: METAVIR F0 (n = 20), F1 (n = 17), F2 (n = 20), F3 (n = 20) and F4 (n = 17). Transmission FTIR spectra were acquired in the 4000–400 cm−1 range. Wavenumbers were selected by genetic algorithm (GA) according to their diagnostic performance as assessed by a partial least squares discriminant analysis (PLS-DA) model using a training and a validation set to differentiate severe stages of fibrosis from mild or moderate ones. The GA procedure was applied 50 times on randomly selected sets. Furthermore, the best set of wavenumbers was re-tested in 1000 randomly selected validation sets. Wavenumbers selected by GA corresponded to functional groups present in lipids, proteins, and carbohydrates. This model allowed to identify patients with cirrhosis (METAVIR F4), patients with advanced fibrosis (METAVIR F3 and F4), and patients with significant fibrosis (METAVIR F2, F3 and F4), with AUROC (Area Under the Receiver Operating Characteristic) of 0.88, 0.85 and 0.85, respectively. Thus, serum FTIR spectroscopy appears to have a strong potential as a new diagnostic tool for assessing the degree of fibrosis in patients with chronic liver disease.

Know What You Don’t Know: Assessment of Overlooked Microplastic Particles in FTIR Images

Assessing data analysis routines (DARs) for microplastics (MP) identification in Fourier-transform infrared (FTIR) images left the question ‘Do we overlook any MP particles in our sample?’ widely unanswered. Here, a reference image of microplastics, RefIMP, is presented to answer this question. RefIMP contains over 1200 MP and non-MP particles that serve as a ground truth that a DAR’s result can be compared to. Together with our MatLab® script for MP validation, MPVal, DARs can be evaluated on a particle level instead of isolated spectra. This prevents over-optimistic performance expectations, as testing of three hypotheses illustrates: (I) excessive background masking can cause overlooking of particles, (II) random decision forest models benefit from high-diversity training data, (III) among the model hyperparameters, the classification threshold influences the performance most. A minimum of 7.99% overlooked particles was achieved, most of which were polyethylene and varnish-like. Cellulose was the class most susceptible to over-segmentation. Most false assignments were attributed to confusion of polylactic acid for polymethyl methacrylate and of polypropylene for polyethylene. Moreover, a set of over 9000 transmission FTIR spectra is provided with this work, that can be used to set up DARs or as standard test set.

OPTICAL STUDY OF SOL-GEL SPIN-COATING TiO2/Si3N4 MULTILAYERS ON GLASS SUBSTRATES

In this work, we have adopted a sol-gel spin-coating technique and prepared alternative TiO2/Si3N4 multilayers on glass substrates. These alternating layers of TiO2/Si3N4 thin film samples were calcinated at two different temperatures and studied for their optical performance. The optical properties of fabricated thin films were investigated by UV-Visible spectrophotometer, X-ray diffractometer (XRD), Fourier transform infrared (FTIR), and Raman spectroscopy. UV-visible spectra showed broader and higher optical reflectance in the visible spectral region. FTIR transmission spectra show Ti-O-Ti and Si-N stretching modes at around 600 and 881 cm-1. XRD pattern confirmed the presence of anatase-TiO2 and α-Si3N4 phases. Finally, Raman spectra revealed the presence of anatase-TiO2 and N-Si vibration modes.

Infrared optical properties of SiO2 films on silicon substrate under different temperatures

SiO2 is a very important low refractive index film material that can operate in the UV to mid-IR regions. The SiO2 films used were deposited on Si substrates by different deposition techniques. We designed and manufactured a high-temperature infrared spectrum measuring equipment connected with a Fourier transform infrared (FTIR) spectrometer; the measuring temperature could range from room-temperature to 600°C. The FTIR transmission spectra of SiO2 films under different working temperatures were measured in the wavenumber region from 4000 to 400 cm − 1. From the measured spectra, it can be seen that IBS-SiO2 and IAD-SiO2 films are more stable and operating temperature can reach 400°C. EB-SiO2 film is worse and operating temperature is only 300°C. Complex dielectric functions of SiO2 films under different temperature conditions were calculated from FTIR transmittance spectra, and the best fitted method was obtained for calculating optical constants of dielectric materials in the high temperature condition. The results show that the structure of the Si-O-Si network in IBS-SiO2 films was the most stable structure. The experimental results were of great significance to practical application.

NiO nanoparticles: Facile route synthesis, characterization and potential towards third generation solar cell

Abstract In this work, nickel oxide nanoparticles (NiO NPs) have been synthesized through highly versatile and cost-efficient chemical precipitation process using polyvinylpyrrolidone (PVP) as a surfactant. The X-ray diffraction (XRD), UV–Visible (UV–Vis), Thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) techniques were employed to characterize the synthesized NiO NPs. The XRD pattern studies revealed that the NiO NPs have a face-centered cubic (FCC) structure and the mean crystallite size of about 7 nm. The optical band gap of 2.88 eV estimated from the tauc plot of thin film UV–vis absorption spectra. FTIR transmission spectra display a prominent band at ∼433 cm−1, which coincides with the bending vibration of Ni–O bond. The prepared NiO NPs retain the prodigious potential as a transparent electrode towards the solar photovoltaic (PV) cell.

Water adsorption on silica and calcium‐boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

AbstractAdsorption isotherm of water on silica (modeled with fused quartz) and calcium‐boroaluminosilicate (Ca‐BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub‐monolayer regime (<30% RH), differences between the water spectra on fused quartz and Ca‐BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x‐ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca‐BAS surfaces diminishes as the humidity increases. In the multilayer regime (>60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.

Determining the continuous thermo-optic coefficients of chalcogenide glass thin films in the MIR region using FTIR transmission spectra.

A new method (FTIR continuous dn / dT method, n is refractive index and T temperature) for measuring the continuous thermo-optic coefficients of thin transparent films in the mid-infrared (MIR) spectral region is introduced. The technique is based on Fourier transform infrared (FTIR) transmission spectra measured at different temperatures. It is shown that this method can successfully determine the thermo-optic coefficient of chalcogenide glass thin films (of batch compositions Ge20Sb10Se70 at. % (atomic %) and Ge16As24Se15.5Te44.5 at. %) over the wavelength range from 2 to 25 µm. The measurement precision error is less than ± 11.5 ppm / °C over the wavelength range from 6 to 20 µm. The precision is much better than that provided by the prism minimum deviation method or an improved Swanepoel method.

Optimization of Infrared Microscopy to Assess Secondary Structure of Insulin Molecules Within Individual Subvisible Particles in Aqueous Formulations

The analysis of subvisible particles is currently challenging but pivotal to the understanding and control of the quality of protein therapeutics. While a range of characterization methods is available for subvisible particles, information on the protein conformation in a particle—considered a possible parameter in eliciting unwanted immunogenicity of protein therapeutics—is especially challenging in the lower micrometer range using existing analytical technologies. Using 6 different protein particle populations, we show that transmission Fourier transform infrared (FTIR) microscopy can determine protein secondary structure in single particles down to 10 μm. The analytical setup presented here is able to immobilize protein particles and obtain transmission FTIR spectra on individual protein particles in their intact aqueous environment. Spectra of dried particles, on the other hand, were found to occasionally differ from spectra of particles in aqueous environment. In summary, using the analytical setup described in this study, transmission FTIR microscopy uniquely provides information on single protein particles in particle populations in their aqueous environment without interference from the background protein solution.

FTIR and Raman spectroscopic studies of selenium nanoparticles synthesised by the bacterium Azospirillum thiophilum

Vibrational (Fourier transform infrared (FTIR) and Raman) spectroscopic techniques can provide unique molecular-level information on the structural and compositional characteristics of complicated biological objects. Thus, their applications in microbiology and related fields are steadily increasing. In this communication, biogenic selenium nanoparticles (Se NPs) were obtained via selenite (SeO32−) reduction by the bacterium Azospirillum thiophilum (strain VKM B-2513) for the first time, using an original methodology for obtaining extracellular NPs. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed the Se NPs to have average diameters within 160–250nm; their zeta potential was measured to be minus 18.5mV. Transmission FTIR spectra of the Se NPs separated from bacterial cells showed typical proteinacious, polysaccharide and lipid-related bands, in line with TEM data showing a thin layer covering the Se NPs surface. Raman spectra of dried Se NPs layer in the low-frequency region (under 500cm−1 down to 150cm−1) showed a single very strong band with a maximum at 250cm−1 which, in line with its increased width (ca. 30cm−1 at half intensity), can be attributed to amorphous elementary Se. Thus, a combination of FTIR and Raman spectroscopic approaches is highly informative in non-destructive analysis of structural and compositional properties of biogenic Se NPs.

Predicting the cell-wall compositions of Pinus radiata (radiata pine) wood using ATR and transmission FTIR spectroscopies

Because plant cell walls vary in their polysaccharide compositions and lignin contents, their monosaccharide compositions and lignin contents are often determined, but these analyses are time consuming and laborious. We therefore investigated Fourier transform infrared (FTIR) spectroscopy coupled with partial least squares (PLS) regression analysis as a way of rapidly predicting the monosaccharide compositions and lignin contents of the cell walls of compression wood (CW) and opposite wood (OW) of the gymnosperm Pinus radiata. The effects were investigated of sample moisture content (ambient or dry) and sample particle size (large particles, < 0.422 mm or small particles, < 0.178 mm) of milled wood on attenuated total reflectance (ATR) and transmission FTIR spectra, as well as the PLS-1 models and subsequent predictions. PLS-1 models were built using mixtures of CW and OW as the training set, to provide a linear range of monosaccharide compositions and lignin contents. Models were externally validated by predicting another set of wood mixtures before predicting CW and OW of a separate test set. Most of the monosaccharide amounts in the separate test set were best predicted by ATR spectroscopy of ambient large particles, achieving the lowest standard error values for the monosaccharides arabinose (0.36%), xylose (1.05%), galactose (1.79%), glucose (6.32%), and 4-O-methylglucuronic acid (0.20%). The results show the feasibility of using ATR spectroscopy of ambient large particles for the rapid prediction of monosaccharide compositions and lignin contents of plant cell walls.

Rapid detection of talcum powder in tea using FT-IR spectroscopy coupled with chemometrics.

This paper investigated the feasibility of Fourier transform infrared transmission (FT-IR) spectroscopy to detect talcum powder illegally added in tea based on chemometric methods. Firstly, 210 samples of tea powder with 13 dose levels of talcum powder were prepared for FT-IR spectra acquirement. In order to highlight the slight variations in FT-IR spectra, smoothing, normalize and standard normal variate (SNV) were employed to preprocess the raw spectra. Among them, SNV preprocessing had the best performance with high correlation of prediction (RP = 0.948) and low root mean square error of prediction (RMSEP = 0.108) of partial least squares (PLS) model. Then 18 characteristic wavenumbers were selected based on a hybrid of backward interval partial least squares (biPLS) regression, competitive adaptive reweighted sampling (CARS) algorithm and successive projections algorithm (SPA). These characteristic wavenumbers only accounted for 0.64% of the full wavenumbers. Following that, 18 characteristic wavenumbers were used to build linear and nonlinear determination models by PLS regression and extreme learning machine (ELM), respectively. The optimal model with RP = 0.963 and RMSEP = 0.137 was achieved by ELM algorithm. These results demonstrated that FT-IR spectroscopy with chemometrics could be used successfully to detect talcum powder in tea.

Interpretation of infrared spectra for OM characterization of soil structural surfaces of Bt‐horizons

AbstractThe surfaces of macropores or aggregates can act as hot spots for biogeochemical processes and solute transport during preferential flow. For the characterization of organic matter (OM) at macropore surfaces non‐destructive methods have been applied such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). However, effects of organic components on DRIFT signal intensities are often difficult to distinguish from those of mineral components. Here, DRIFT spectra from intact earthworm burrow walls and coated cracks were re‐evaluated to improve the interpretation of C–H and C=O bands. We compared DRIFT and transmission Fourier transform infrared (FTIR) spectra of entire samples that were from the same pedogenetic soil horizon (Bt) but different in mineral composition and texture (i.e., glacial till vs. loess). Spectra of incinerated samples were subtracted from the original spectra. Transmission FTIR and DRIFT spectra were almost identical for entire soil samples. However, the DRIFT spectra were affected by the bulk mode bands (i.e., wavenumbers 2000 to 1700 cm−1). These bands affected spectral resolution and reproducibility. The ratios between C–H and C=O band intensities as indicator for OM quality obtained with DRIFT were smaller than those obtained from transmission FTIR. The results demonstrated that DRIFT and transmission FTIR data required separate interpretations. DRIFT spectroscopy as a non‐destructive method for analyzing OM composition at intact surfaces in structured soils could be calibrated with information obtained with the more detailed transmission FTIR and complementary methods. Spectral subtraction procedure was found useful to reduce effects of mineral absorption bands. The improved DRIFT data may be related to other soil properties (e.g., cation exchange capacity) of hot spots in structured soils.

Comparison of transmission FTIR, ATR, and DRIFT spectra: implications for assessment of bone bioapatite diagenesis

Evaluation of diagenesis in bioapatite samples is an important step for screening bone and tooth samples for stable isotope analysis to ensure in vivo signatures are obtained. Fourier transform infrared (FTIR) spectroscopy is one tool used to evaluate diagenesis by anthropological geochemists and commonly employs calculating the infrared splitting factor (IR-SF) and carbonate-to-phosphate ratio (C/P). There are three commonly used sample preparation techniques for vibrational spectroscopy: transmission FTIR, attenuated total reflection (ATR), and diffuse reflectance infrared Fourier transform (DRIFT). Each technique characterizes the internal vibrations of particular molecular groups, such as carbonate (CO3) and phosphate (PO4), using different optical properties to detect absorbance bands. Spectra are correlated between techniques using correction equations that account for differences in optical properties. Traditionally, anthropologists have used spectra produced by transmission FTIR to assess diagenesis, most commonly using two indices (IR-SF and C/P); however, recently the ATR and DRIFT techniques have been used as an alternative to transmission FTIR. The spectra produced by the three techniques are thought to be interchangeable in calculating the indices used to assess diagenesis. In this study, we evaluated the interchangeability of the three FTIR techniques by analyzing 452 prehistoric and modern bioapatite samples. Results indicate that IR-SF and C/P values are not equivalent between the three techniques. However, ATR produced more reliable results and was comparable to transmission FTIR. The DRIFT method showed much lower resolution, and did not distinguish between modern and prehistoric bioapatite samples as clearly.

Influence of hydrogen and hydrogen/methane plasmas on AlN thin films

Polycrystalline aluminum nitride (AlN) thin films are exposed to hydrogen and hydrogen/methane plasmas at different conditions. The latter plays an indispensable role in the subsequent deposition of nanocrystalline diamond thin films on AlN. The changes of AlN properties are investigated by means of Fourier transform infrared (FTIR) and Raman spectroscopies as well as atomic force microscopy. The E1(TO) and E22 phonon mode frequencies blue-shift after the exposure to plasmas. The damping constant of E1(TO) phonon, calculated from FTIR transmission spectra using the factorized model of a damped oscillator, and the width of E22 peak in Raman spectra decrease with increasing substrate temperature till the decomposition of AlN thin film becomes notable. It is proven that these changes are driven by the plasmas as annealing in vacuum does not induce them.

Complete Elemental Analysis of Low-k a-SiC:H Thin Films by Transmission FTIR Spectroscopy

Fourier transform infrared (FTIR) spectroscopy is a popular technique for qualitatively investigating the chemical bonding of low dielectric constant (low-k) materials utilized in nanoelectronic Cu interconnects. However, quantitative FTIR analysis of low-k materials with widely varying stoichiometry has proven challenging due to numerous optical interference effects, variations in IR absorption strength with optical constants, and a negligible IR activity for homopolar bonds. In this paper, these challenges are overcome to demonstrate full elemental composition analysis by applying multivariate partial least squares (PLS) modeling to the true IR absorbance spectra obtained using previously described methods for eliminating optical interference effects from thin film FTIR spectra. To demonstrate the validity of this approach, transmission FTIR spectra were collected from a series of low-k a-SiC:H thin films with hydrogen content ranging from 25–60%. The elemental concentrations determined from PLS analysis of the corrected low-k a-SiC:H FTIR spectra were found to be in agreement to within ±5% of results obtained from independent nuclear reaction analysis and Rutherford backscattering measurements. These results demonstrate a clear path for establishing transmission FTIR as a quantitative metrology for full compositional analysis (elemental and chemical bond) for a wide range of thin film materials.

Application of the simultaneous measurement system of WAXD, SAXS and transmission FTIR spectra to the study of structural changes in the cold- and melt-crystallization processes of trans-1,4-polyisoprene

The newly developed system of simultaneous time-dependent measurements of wide-angle X-ray diffraction, small-angle X-ray scattering and transmission-type Fourier-transform infrared spectra has been applied to study the structural changes in the melt- and cold-crystallization processes of trans-1,4-polyisoprene (TPI). For the melt-isothermal crystallization process at 40 °C, the domains of relatively higher density with approximately 220 Å radius formed at first as the intermediate state, where the chain conformation was speculated to be considerably disordered. As time passed, the correlation length ξ between these domains decreased until they joined together to form the stacked lamellar structure. In these lamellae, the crystal lattices of the regular α form were created. When the isothermal crystallization was investigated at 30 °C, the intermediate-phase regularization caused the α- and β-crystalline forms to mix. In the cold-crystallization process or the heating process that started from the melt-quenched glass below −100 °C, TPI was found to crystallize at first to the β-form at approximately −55 °C, which transformed to the α-form at 50 °C via the amorphous phase as observed above. Simultaneous time-dependent measurements of WAXSD, SAXS and Fourier-transform infrared (FTIR) spectra have been performed to study the structural changes in the melt- and cold-crystallization processes of trans-1,4-polyisoprene (TPI). In the melt-isothermal crystallization process, the domains of relatively higher density were formed at first as the intermediate state, which approached each other to form the stacked lamellar structure. In the cold-crystallization process from melt-quenched glass, TPI crystallized to the β-form at −55 °C, which transformed to the α-form at 50 °C via the amorphous phase.

Confined rapid thermolysis studies of ammonia borane

Thermochemical calculations of ammonia borane (AB, H3NBH3), which has a hydrogen content of 19.6% by weight, indicate that it has the potential to boost specific impulse in chemical propulsion applications due to its high hydrogen content and the moderate exothermicity of decomposition. Research to date on AB decomposition has focused on relatively slow heating rates. These studies have shown that the mass lost due to decomposition increases with increasing heating rate. This trend has been confirmed in this work, as mass loss continues to increase up to 50K/min, the limit of most TGA/DSC instruments. In this research effort, confined rapid thermolysis was used to examine the decomposition of AB under isothermal conditions. Fourier transform infrared (FTIR) spectroscopy and time-of-flight mass spectrometry (ToF-MS) were employed to identify the gaseous products, which include H2, NH3, H2NBH2, and c-N3B3H6. The decomposition resulted in significant condensed-phase products as well, which were pressed into a KBr pellet and examined with FTIR spectroscopy. FTIR transmission spectra of the condensed-phase products with several heating durations show the disappearance of absorption bands of AB and appearance of bands attributed to polymeric species. Condensable gas-phase products were also collected from the stream of decomposition products, and FTIR spectroscopy showed they have absorption bands similar to the polymeric species, indicating that the H2NBH2 will readily condense out of the gas-phase products and polymerize at low temperatures.

FT-IR Study of CO2 Adsorption in a Dynamic Copper(II) Benzoate−Pyrazine Host with CO2−CO2 Interactions in the Adsorbed State

A detailed correlation is presented between the in situ Fourier transform-infrared (FT-IR) spectra of adsorbed CO2, CuBzPyz host bands, and CO2 adsorption sites using previously reported crystal structures of CO2-loaded CuBzPyz and CO2 adsorption isotherms. Through the analysis of both in situ attenuated total reflectance FT-IR spectra taken at several points on the high pressure isotherm and in situ transmission FT-IR spectra acquired at low pressures and cryogenic temperatures, we provide additional insight into the pore-filling mechanism of CO2 on the structurally dynamic CuBzPyz host. The FT-IR spectrum of adsorbed CO2 shows distinct ν2 and ν3 spectral features that can be attributed to known CO2 adsorption sites observed in the reported crystal structure of the CO2-saturated phase of CuBzPyz. The availability of detailed high quality CO2-loaded structural data for CuBzPyz makes this system a case study for associating infrared spectral features with CO2 adsorption sites and should prove valuable for future interpretations of CO2 host−guest and guest−guest interactions when X-ray quality structural data is unavailable.

Diffusion and Structure of Water in Polymers Containing N-Vinyl-2-pyrrolidone

Poly(N-vinyl-2-pyrrolidone) (PVP), a water-soluble polymer, is known for its excellent biocompatibility. It is generally recognized that the properties of polymers may be profoundly affected by the structure of water absorbed in them. In this study, Fourier transform infrared (FT-IR) in attenuated total reflection (ATR) and transmission mode was performed to examine the diffusion and structure of water in PVP and its copolymers. The obtained spectra were analyzed using two-dimensional (2D) IR with the aid of density functional theory (DFT) calculations. The 2D IR of time-resolved FT-IR/ATR spectra shows that type II water between 3300 and 3500 cm(-1) occurs earlier during the water absorption process, which is also demonstrated by transmission FT-IR at the initial stage of water absorption. Conversely, type II water changes last when desorption takes place. Results from DFT calculations indicate that type II water might be monomeric or dimeric water molecules interacting with a carbonyl group in the pyrrolidone moiety. Furthermore, it is found that vibrations less than 3300 cm(-1) (type I water) arise from water molecules involved in a carbonyl group interacting with more than two water molecules. It is reasonable that the transmission FT-IR spectra of film with an extra low water amount hardly show vibration bands below 3300 cm(-1); however, this region is distinct in the FT-IR/ATR spectra of fully swollen film. In addition, vibration bands between 3800 and 3500 cm(-1) (type III water) are assigned to free water or water with relatively weak hydrogen bonding, as supported by the transmission FT-IR spectra of polyacrylonitrile (PAN) and the calculation results. Therefore, the diffusion process and the structures of water in PVP and its copolymers can be successfully accessed on the basis of the 2D IR analysis and DFT calculations.