Hydrogel-based piezoresistive pH sensors: investigations using FT-IR attenuated total reflection spectroscopic imaging

The strong swelling ability of the pH-responsive poly(acrylic acid)/poly(vinyl alcohol) (PAA/PVA) hydrogel makes the development of a new type of sensor possible, which combines piezoresistive-responsive elements as mechanoelectrical transducers and the phase transition behavior of hydrogels as a chemomechanical transducer. The sensor consists of a pH-responsive PAA/PVA hydrogel and a standard pressure sensor chip. However, a time-dependent sensor output voltage mirrors only the physical swelling process of the hydrogel but not the corresponding chemical reactions. Therefore, an investigation of the swelling behavior of this hydrogel is essential for the optimization of sensor design. In this work, Fourier transform infrared (FT-IR) spectroscopic imaging was used to study the swelling of the hydrogel under in situ conditions. In particular, laterally and time-resolved FT-IR images were obtained in the attenuated total reflection mode and the entire data set of more than 80,000 FT-IR spectra was evaluated by principal component analysis (PCA). The first and third principal components (PCs) indicate the swelling process. Molecular changes within the carboxyl groups were observed in the second and fourth PC and identified as key processes for the swelling behavior. It was found that time-dependent molecular changes are similar to the electrical sensor output signal. The results of the FT-IR spectroscopic images render an improved chemical sensor possible and demonstrate that in situ FT-IR imaging is a powerful method for the characterization of molecular processes within chemical-sensitive materials.     

High speed and low power consumption of superlattice-like Ge/Sb<Subscript>70</Subscript>Se<Subscript>30</Subscript> thin films for phase change memory application

In comparison to Ge₂Sb₂Te₅ (GST) and pure Sb₇₀Se₃₀ (SbSe) thin films, superlattice-like (SLL) Ge/Sb₇₀Se₃₀ (Ge/SbSe) has a higher crystallization temperature, larger crystallization activation energy, better data retention and lower power consumption. SLL Ge/SbSe thin films with different thickness of Ge and SbSe layers were prepared by magnetron sputtering system. The amorphous-to-crystalline transitions of SLL Ge/SbSe thin films were investigated through in situ film resistance measurement. The crystallization activation energy of SLL Ge/SbSe thin films was calculated from a Kissinger plot. The data retention time was estimated through isothermal time-dependent resistance measurement by Arrhenius equation. The phase structure of the thin films annealed at different temperatures was investigated by using X-ray diffraction. Phase change memory cells based on the SLL [Ge(8 nm)/SbSe(5 nm)]₄ thin films were fabricated to test and evaluate the switching speed and operation consumption.     

Spectral pattern recognition of in situ FT-IR spectroscopic reaction data using minimization of entropy and spectral similarity (MESS): application to the homogeneous rhodium catalyzed hydroformylation of isoprene

An improved algorithm using minimization of entropy and spectral similarity (MESS) was tested to recover pure component spectra from in situ experimental Fourier transform infrared (FT-IR) reaction spectral data, which were collected from a homogeneous rhodium catalyzed hydroformylation of isoprene. The experimental spectra are complicated and highly overlapping because of the presence of multiple intermediate products in this reaction system. The traditional entropy minimization method fails to resolve real reaction mixture spectra, but MESS can successfully reconstruct pure component spectra of unknown intermediate products for real reaction systems by the addition of minimization of spectral similarity. The quantitative measure of spectral similarity between two spectra was given by their inner products. The results indicate that MESS is a stable and useful algorithm for spectral pattern recognition of highly overlapped experimental reaction spectra. Comparison is also made between MESS, entropy minimization, simple-to-use interactive self-modeling mixture analysis (SIMPLISMA), interactive principle component analysis (IPCA), and orthogonal projection approach-alternating least squares (OPA-ALS).     

Luminescent homo- and hetero-metallic hybrid molecular materials constructed by covalent grafting

In this paper, 3-(triethoxysilyl)-propyl isocyanate (abbreviated as TESPIC) was modified by ethylparaben (EPB) to produce corresponding organic-inorganic monomers (EPB-TESPIC) with two components equipped with covalent bonds, which not only can coordinate to RE ions (Tb³⁺ and Eu³⁺) but also act as a sol-gel precursor. Luminescent hybrid materials consisting of terbium-europium complex, covalently bonded to silica-based network, have been obtained in situ via a sol-gel approach. Proton nuclear magnetic resonance spectroscopy (¹HNMR) and Fourier transform infrared spectroscopy (FT-IR) were applied to characterize the structure of EPB-TESPIC. UV-visible, phosphorescence, and luminescence spectra were obtained to characterize the photophysical properties of the obtained hybrid material. Through co-hydrolysis and polycondensation, Tb³⁺ and Eu³⁺ can be introduced into the same organic-inorganic hybrid monomer, forming Si-O backbones. The experimental results show that the strong luminescence of rare-earth ions substantiates the optimum energy match and effective intramolecular energy transfer between the triplet state energy of coordination complex and the emissive energy level of the rare-earth ions. The hybrid material systems are expected to have potential applications in photophysical sensors.     

Application of two-dimensional correlation spectroscopy to chemometrics: self-modeling curve resolution analysis of spectral data sets

This paper demonstrates the use of two-dimensional (2D) correlation spectroscopy in conjunction with alternating least squares (ALS) based self-modeling curve resolution (SMCR) analysis of spectral data sets. This iterative regression technique utilizes the non-negativity constraints for spectral intensity and concentration. ALS-based SMCR analysis assisted with 2D correlation was applied to Fourier transform infrared (FT-IR) spectra of a polystyrene/methyl ethyl ketone/deuterated toluene (PS/MEK/d-toluene) solution mixture during the solvent evaporation process to obtain the pure component spectra and then the time-dependent concentration profiles of these three components during the evaporation process. We focus the use of asynchronous 2D correlation peaks for the identification of pure variables needed for the initial estimates of the ALS process. Choosing the most distinct bands via the positions of asynchronous 2D peaks is a viable starting point for ALS iteration. Once the pure variables are selected, ALS regression can be used to obtain the concentration profiles and pure component spectra. The obtained pure component spectra of MEK, d-toluene, and PS matched well with known spectra. The concentration profiles for components looked reasonable.     

Luminescence of novel terbium complex/inorganic/polymeric hybrid materials based on sol-gel technology

In this paper, a new terbium complex/inorganic/polymeric molecular hybrid material was prepared and its optical properties were studied. At first, 4-nitrobenzoic acid was modified by (3-aminopropyl) trimethoxysilane to form a precursor and coordinated with terbium ion. Then it was polymerized with inorganic host tetraethoxysilane or polymer host polyvinyl alcohol and formed hybrid material. ¹H NMR Fourier transform infrared (FT-IR), scanning electron microscope and TGA were applied to characterize the structure of the precursor. UV-vis spectrophotometer and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb³⁺ substantiates optimum energy couple and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb³⁺.     

Adsorption density of spherical cetyltrimethylammonium bromide (CTAB) micelles at a silica/silicon surface

In situ Fourier transform infrared internal reflection spectroscopy (FT-IR/IRS) was used to calculate the adsorption density values for spherical cetyltrimethylammonium bromide (CTAB) micelles at the silica/silicon (SiO2/Si) surface based on a previously developed adsorption density equation. Recent advances in atomic force microscopy (AFM) imaging methodology have led to the ability to image surface micelles, which was not possible previously. These AFM images have been used to independently calculate adsorption density values through offline fast Fourier transform (FFT) analysis. The adsorption density values measured from in situ FT-IR/IRS spectra and from AFM images showed good agreement and provide further validation of the FT-IR/IRS adsorption density equation in the low concentration range.     

Infrared and nuclear magnetic resonance spectroscopic study of secondary amide hydrogen bonding in benzoyl PABA derivatives (retinoids)

Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) data are used to characterize the hydrogen bonding of the secondary amide N-H group of several structurally similar benzoyl derivatives of p-aminobenzoic acid esters (retinoids) in chloroform solution. The amide N-H can form intermolecular hydrogen bonds to several proton acceptors in these molecules or it can form an intramolecular hydrogen bond to a fluorine or oxygen atom in some of the molecules. The concentration dependence of the solution N-H infrared absorption bands is used to determine the formation of intramolecular and/or intermolecular H-bonds. Proton NMR spectra were obtained from deuterated chloroform solutions and the sec-amide N-H resonance was assigned for each compound. The downfield shift in the N-H resonance is correlated to intramolecular H-bond formation. Also, the NMR spectra of fluorine-containing compounds provide J(F-H) through-space coupling values. Using infrared and NMR data, the relative intramolecular hydrogen bond strengths (N-H...F or N-H...O) of the compounds are approximately ranked.     

In Situ Fourier transform infrared spectroscopic study of the thermal degradation of isotactic poly(propylene)

The conformational change of isotactic poly(propylene) (iPP) during the thermal degradation process has been carefully studied by in situ Fourier transform infrared (FT-IR) spectroscopy. This new method of studying thermal degradation of iPP not only shows the conventional kinetic parameter information of thermal degradation such as the degradation activation energy DeltaE and the degradation factor n, which are in accord with the results of traditional thermogravimetry experiments, but also indicates that many significant molecular structure changes occur during the thermal degradation process that come from some characteristic absorption band changes of in situ FT-IR. A multivariate approach, principal components analysis (PCA), is applied to the analysis of infrared (IR) data, and the results further confirm the multi-step processes of the thermal degradation of iPP. Above all, this is a new application to polymer thermal degradation by in situ FT-IR that connects the intermediate conformational change with final results during thermal degradation.     

In situ ATR-FT-IR kinetic studies of molecular transport and surface binding in thin sol-gel films: reactions of chlorosilane reagents in porous silica materials

ATR-FT-IR spectroscopy was employed to study the kinetics of transport and binding within thin silica sol-gel films. Studies of transport of several nonbinding probe molecules n-heptane, toluene, and 2-propanol, showed that slow diffusion occurs within the micropores of the sol-gel films which could be modeled as a single-exponential accumulation in agreement with numerical models for diffusion in constricted pores. The rate of transport into the film was found to decrease for molecules that interact strongly with the silica surface, which is consistent with adsorption inhibiting the transport of molecules through the pores. In situ spectroscopic studies of surface reactions with diphenylchlorosilane (DP-SiCl) reveal that DPSiCl reacts quickly with surface water to form diphenylhydroxysilane (DPSiOH), the reactive species detected within the film. Analysis of the time-dependent infrared spectra reveals both transport and surface-binding steps in the reaction kinetics. From the magnitudes of the rate constants and the corresponding pure component spectra, it is determined that the surface-binding component is responsible for accumulation of most of the silane at the silica surface. Ex situ spectroscopic studies confirm that Si-O-Si bond formation occurs at room temperature in these sol-gel films. Studies of chlorosilane reactions at silica surfaces pretreated with triethylamine were conducted to investigate the influence of amines on this chemistry; it was determined that the amine enhances the transport of more reagent molecules to the silica surface while the intrinsic rate of the binding reaction is not significantly changed.     

Sn-rich phase coarsening during isothermal annealing for as-soldered Sn–Ag–Cu solder

The effect of Sn-rich coarsening in Sn–Ag–Cu solder joints produced by isothermal annealing was investigated. The isothermal annealing temperatures employed were from 30 to 150 °C for 24 h up to 1,008 h of annealing time. An Infinite Focus Measurement system (IFM®) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) were used for microscopic analysis and elemental analysis, respectively. As the annealing time and temperature increased, a eutectic component Cu, diffused into the Sn-rich phases, coarsening the Sn-rich phases, and the activation energy value for the coarsening was determined to be 41 kJ/mol.     

In situ high-temperature visible microspectroscopy for volcanic materials

In situ high-temperature visible microspectroscopy has been developed in order to study color change kinetics of volcanic materials. Olivine thin sections put on a synthetic alumina plate are heated on a heating stage at 600-800 degrees C under a visible microspectroscope. Changes in visible absorption spectra are monitored every 60 s for 5 hours. The obtained high-temperature visible spectra showed a gradual increase with time in absorbance in the shorter wavelength region (400-600 nm). The 430 nm absorbance (ligand field transition of Fe3+ increased more with time at higher temperatures. Assuming diffusional transport in plane sheets, apparent diffusion coefficients were determined at temperatures of 600-800 degrees C. The activation energy for this diffusion in olivine is 208 +/- 17 kJ/mol. This activation energy value is similar to those for the metal vacancy diffusion in olivine. This newly developed in situ high-temperature visible microspectroscopy can provide kinetic measurements of visible spectral change of materials at high temperatures such as volcanic materials.     

香草醛改性壳聚糖对镉离子的吸附热力学和动力学

研究了微波辐射条件下香草醛改性壳聚糖(V-CTS)对Cd2+离子的吸附性能,测定了吸附等温线和吸附动力学曲线。结果表明,该吸附剂对Cd2+离子的吸附行为符合Freundlich吸附等温式,在298～318K温度范围内,焓变ΔH=24.22kJ/mol,表明吸附是吸热过程。吸附动力学符合Lagergren二级吸附速率方程,反应活化能为25.58kJ/moL,表明V-CTS对金属离子的吸附由化学反应控制,而非扩散控制。吸附剂解吸再生循环使用4次后,镉离子的吸附容量仅减少18.9%,该吸附剂具有较好地再生使用性。     

Remote monitoring of a multi-component liquid-phase organic synthesis by infrared emission spectroscopy: the recovery of pure component emissivities by band-target entropy minimization

A liquid-phase cycloaddition reaction near ambient temperature involving dimethyl acetylenedicarboxylate (DMAD) and cyclopentadiene (CP) as reactants was measured using a conventional Fourier transform infrared (FT-IR) spectrometer with an emission accessory. Two semi-batch experiments were performed and a total of 55 spectra were collected using a DTGS detector. Band-target entropy minimization (BTEM), a pure component spectral reconstruction technique, was applied to analyze the data set to retrieve the pure component emission spectrum from the reaction system. The estimated emission spectra of the solvent chloroform, DMAD, CP, and product, namely dimethyl bicyclo[2.2.1]-2,5-heptadiene-2,3-dicarboxylate, were all reconstructed with rather good quality. The estimated emission spectra are similar to independent FT-IR spectra of the same cycloaddition reaction. Using a least squares fit, the relative concentration profiles of the species are obtained. Because this appears to be the first time that a liquid-phase reaction has been monitored by infrared emission spectroscopy, further improvements and opportunities for general multi-phase liquid reaction monitoring are discussed.     

Titanium dioxide doped polyaniline

Titanium dioxide doped polyaniline has been prepared by in situ polymerization. TiO₂ nanoparticles with an average diameter about 20 nm were used as a dopant of polyaniline. The doping effect of TiO₂ was characterized and evaluated by scanning electron microscopy (SEM), Fourier transformation infrared spectroscopy (FT-IR), energy dispersive spectrometry (EDS) and electrical conductivity measurement. SEM study shows that TiO₂ nanoparticles have a strong effect on the morphology of composites. The FT-IR spectra reveal that the interaction between TiO₂ and polyaniline (PANI) is primarily based on the formation of H-bonding. Electrical conductivity measurements indicate that the conductivity of composites at low TiO₂ content is much higher than that of neat PANI, while with the increasing contents of TiO₂, the conductivity shows an orderly decrease.     

Thermokinetic study on growth process of CdS nanocrystals by in situ microcalorimetry

In situ microcalorimetry was used to investigate the energy evolution during CdS nanocrystal growth process. It can provide important information for controlling crystal growth. The CdS nanospheres were synthesized in the glycol-water system at room temperature. The energy change of CdS nanocrystal growth process was measured by a microcalorimeter. The microcalorimetric curve shows a strong exothermic peak. On the basis of the experimental result, the rate constant and the activation Gibbs energy have been obtained. The CdS nanocrystals were characterized by X-ray diffraction, scanning electron microscope and photoluminescence spectra. The morphology evolution can be well connected with the energy change.     

Calibration-free estimates of batch process yields and detection of process upsets using in situ spectroscopic measurements and nonisothermal kinetic models: 4-(dimethylamino)pyridine- catalyzed esterification of butanol

In this paper, we report the use of an NIR fiber-optic spectrometer with a high-speed diode array for calibration-free monitoring and modeling of the reaction of acetic anhydride with butanol using the catalyst 4-(dimethylamino)pyridine in a microscale batch reactor. Acquisition of spectra at 5 ms/scan gave information relevant for modeling these fast batch processes with a single multibatch kinetic model. Nonlinear fitting of a first-principles model directly to the reaction spectra gave calibration-free estimates of time-dependent concentration profiles and pure component spectra. The amount of catalyst was varied between different batches to permit accurate estimation of its effect in the multiway model. A wide range of different models with increasing complexity could be fit to each batch individually with low residuals and apparent low lack of fit. However, only one model properly estimated the concentration profiles when all five batches were fitted simultaneously in a multiway kinetic model. Inclusion of on-line temperature measurements and use of an Arrhenius model for the estimated rate constant gave significantly improved model fits compared to an isothermal kinetic model. Augmentation of prerun batches with data from an additional batch permitted model-based forecasts of reaction trajectories, reaction yield, reaction end points, and process upsets. One batch with added water to simulate a process upset was easily detected by the calibration free process model.     

Characterization of infrared matrix-assisted laser desorption ionization samples by Fourier transform infrared attenuated total reflection spectroscopy

Fourier transform infrared attenuated total reflection (FT-IR ATR) spectroscopy was used to characterize thin films of succinic acid, a matrix compound commonly used with infrared matrix-assisted laser desorption ionization (IR-MALDI) mass spectrometry. IR spectra of succinic acid thin films deposited alone and in combination with the analyte biomolecules insulin and cytochrome c were obtained by FT-IR ATR spectroscopy. Spectra of analyte and matrix alone were similar to those obtained previously from KBr pellets, Nujol mull, or thin-film absorption, although the ATR spectra have significantly lower background interferences. Thin films deposited from mixtures of water and methanol have additional peaks compared to films deposited from a methanol solution. These additional peaks are attributed to carboxylate groups stabilized by residual water molecules. No evidence was found to suggest that residual water absorption contributes to absorption at wavelengths typically used for IR-MALDI. Absorption of energy by analyte vibrational modes with rapid energy transfer to the matrix is suggested as a contributor to desorption and ionization consistent with the FT-IR ATR results.     

Quantitative analysis of the in situ Fourier transform infrared absorption and emission spectrum of gas-phase SiO (Deltav = 1 and 2) produced in Si-N-O fiber growth

The in situ Fourier transform infrared (FT-IR) spectrum of gasphase SiO produced in silicon oxynitride fiber growth has been quantitatively analyzed. Both absorption and emission FT-IR spectra at a spectral resolution of 0.5 cm(-1) were produced from the reaction zone at 1450 degrees C. The fundamental and hot bands were observed with vibrational levels up to v = 7. For the purposes of quantitative analysis the individual vibration-rotation integrated line strengths for the three main isotopes,( 28)SiO,( 29)SiO, and( 30)SiO, were calculated based on ab initio quantum chemical calculations of the electric dipole moment function and the transition moment. Vibrational anharmonicity and Hermann-Wallis correction factors were also incorporated. From the line strengths at specific temperatures and the known Dunham coefficients, the absorbance spectrum was simulated with best fits giving the averaged SiO concentration in the 400 mm reaction zone of 1.0 x 10(17) molecules/cm(3). Such quantitative measurements demonstrate the power of in situ infrared (IR) spectroscopy combined with quantum chemical calculations. The rapid determination of synthetic calibration datasets for chemometric analysis can thus lead to correlation of gas-phase species concentrations with fiber growth properties and subsequently to real-time process control.     

Determination of the percentage of homopolymer component in Ziegler/Natta catalyst linear low-density polyethylene resins using high-temperature cell Fourier transform infrared and partial least squares quantitative analysis technique

A new method for the determination of the percentage of homopolymer component, using high-temperature cell Fourier transform infrared (FT-IR) by partial least squares (PLS) quantitative analysis technique, was developed and applied to Ziegler Natta linear low-density polyethylene (LLDPE). The method is based on the IR spectrum changes between the 730 cm(-1) band and 720 cm(-1) band at the temperature of 110 degrees C, which is near the melting point of the polyethylene. The HD % (the percentage of high-density component, i.e., the percentage of homopolymer component) results obtained by CTREF (CRYSTAF in TREF mode) technique are used as the input data together with the respective FT-IR spectra for PLS analyses to establish a calibration curve. The PLS quality is characterized by a correlation coefficient of 0.997 (cross-validation) using four factors and a root mean square error of calibration (RMSEC) of 0.772. The HD% of the unknown can then be predicted by the PLS software from the unknown FT-IR spectrum. A control resin was tested seven times by CTREF and FT-IR. The HD% of the control resin was 28.59+/-0.88% by CTREF and 29.05+/-2.37% by FT-IR. It was found that the method was applicable for the same comonomer type of LLDPE within a melt index range and density.