Molecular orientation evolution and solvent evaporation during electrospinning of atactic polystyrene using real-time Raman spectroscopy.

Real-time Raman spectroscopy was successfully utilized to monitor solvent evaporation and molecular orientation during electrospinning of atactic polystyrene (a-PS). The use of a binary solvent system of N,N-dimethyl formamide (DMF) and tetrahydrofuran (THF) provided a stable, straight jet during the experiment. The prominent Raman bands centered at 866 cm(-1), 914 cm(-1), and 1004 cm(-1), unique to DMF, THF, and a-PS, respectively, were used to monitor solvent concentration changes along the electrospinning jet for two different a-PS solutions. In addition, the changes in relative intensity for the radial skeletal ring vibration of the aromatic group of a-PS at 623 cm(-1) in two different polarization geometries, ZZ and YY, were monitored for orientation information. This study reports the first quantitative vibrational spectroscopic measurement during the electrospinning process. A significant change in concentration and orientation was observed during the process. The changes are explained in relation to the electrospinning process.

Parallel spectroscopic method for examining dynamic phenomena on the millisecond time scale.

An infrared spectroscopic technique based on planar array infrared (PAIR) spectroscopy has been developed that allows the acquisition of spectra from multiple samples simultaneously. Using this technique, it is possible to acquire spectra over a spectral range of 950-1900 cm(-1) with a temporal resolution of 2.2 ms. The performance of this system was demonstrated by determining the shear-induced orientational response of several low molecular weight liquid crystals. Five different liquid crystals were examined in combination with five different alignment layers, and both primary and secondary screens were demonstrated. Implementation of this high-throughput PAIR technique resulted in a reduction in acquisition time as compared to both step-scan and ultra-rapid-scanning FTIR spectroscopy.

Dynamic infrared study of polyphenylene sulfide using planar array infrared spectroscopy.

Planar array infrared (PA-IR) spectroscopy was used to study polyphenylene sulfide (PPS) at room temperature during the application of a sinusoidal elastic deformation. All of the intensity in the dynamic spectra was contained within the in-phase spectrum, which was expected since the measurements were carried out at room temperature, far below the glass transition temperature. The contributions of chain orientation, sample thinning, and stress-induced band shifts were separated in the dynamic spectra. It was found that the effects of chain orientation and sample thinning canceled each other out. Stress-induced band shifts far below the spectral resolution, on the order of 0.01 cm(-1), were quantified and used to calculate the stress optical coefficients and mode Gruneisen parameters for PPS.

Real-time imaging of crystallization in polylactide enantiomeric monolayers at the air-water interface.

A newly developed planar array infrared reflection-absorption spectrograph (PA-IRRAS) offers significant advantages over conventional approaches including fast acquisition speed, excellent compensation for water vapor, and an excellent capacity for large infrared accessories, e.g., a water trough. In this study, the origin of stereocomplexation in a polylactide enantiomeric monolayer at the air-water interface was investigated using PA-IRRAS. PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of polymer chains during the compression of the monolayers. It was found that a mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the two-dimensional monolayer developed at the air-water interface before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. PA-IRRAS spectra of the stereocomplex exhibited distinct band shifts in crystalline sensitive components, e.g., the vas(C-O-C, h) mode, as well as amorphous-dependent components, e.g., the vs(C-O-C) mode, when compared with the spectra of PLLA alone. On the other hand, time-resolved PA-IRRAS spectra, which were obtained as the films were being compressed, revealed that both monolayers of PLLA and mixed PLLA/PDLA stereocomplex were crystallized into a 10(3)-helix and a 3(1)-helix, respectively, with a distinct band shift in crystalline sensitive components only. Fourier self-deconvolution of the spectra demonstrated that the band shift in crystalline sensitive components is correlated with the intermolecular interaction of polymer chains.

Development of a planar array infrared reflection spectrograph for reflection-absorption spectroscopy of thin films at metal and water surfaces.

Planar array infrared (PA-IR) spectroscopy offers several advantages over Fourier transform infrared (FT-IR) methods, including ultrafast speed (<100 micros temporal resolution) and excellent sensitivity. However, obtaining spectra in the range of 1800 to 1000 cm(-1) of films at the air-water interface remains difficult due to the poor IR reflectivity of water, the extremely low concentration of the thin film on the water subphase, and the interference of water bands. In this study, we report a new planar array infrared reflection spectrograph (PA-IRRS), which has several advantages over conventional approaches. This instrument can record sample and reference spectra simultaneously with an instrumental setup that is the same as that of a single-beam instrument by splitting the incident infrared beam into two sections on a plane mirror (H) or a water trough. With this design, the instrument can accommodate large infrared accessories, such as a water trough, without a loss of infrared beam intensity. Water bands can be subtracted to obtain a high-quality spectrum for poly(L-lactic acid) Langmuir film on the water subphase with a resolution of about 6 cm(-1) in 10.8 s. Hence, this PA-IRRS system has great potential for investigating the time-resolved dynamics of a broad range of Langmuir films, such as cellular membranes or biopolymers, on the water subphase.

High-throughput reactor system with individual temperature control for the investigation of monolith catalysts.

A high-throughput parallel reactor system has been designed and constructed to improve the reliability of results from large diameter catalysts such as monoliths. The system, which is expandable, consists of eight quartz reactors, 23.5 mm in diameter. The eight reactors were designed with separate K type thermocouples and radiant heaters, allowing for the independent measurement and control of each reactor temperature. This design gives steady state temperature distributions over the eight reactors within 0.5 degrees C of a common setpoint from 50 to 700 degrees C. Analysis of the effluent from these reactors is performed using rapid-scan Fourier transform infrared (FTIR) spectroscopic imaging. The integration of this technique to the reactor system allows a chemically specific, truly parallel analysis of the reactor effluents with a time resolution of approximately 8 s. The capabilities of this system were demonstrated via investigation of catalyst preparation conditions on the direct epoxidation of ethylene, i.e., on the ethylene conversion and the ethylene oxide selectivity. The ethylene, ethylene oxide, and carbon dioxide concentrations were calibrated based on spectra from FTIR imaging using univariate and multivariate chemometric techniques. The results from this analysis showed that the calcination conditions significantly affect the ethylene conversion, with a threefold increase in the conversion when the catalyst was calcined for 3 h versus 12 h at 400 degrees C.

Experimental aspects of asynchronous rapid-scan fourier transform infrared imaging.

In the asynchronous, rapid-scan approach to Fourier transform infrared (FT-IR) imaging, data sampling is not correlated with the zero crossings of the interference fringes of the HeNe reference laser. The success of this data collection scheme depends on the reproducibility of the clock signals driving the interferometer mirror and focal plane array data collection. In previous studies, it was shown that this implementation provides for markedly faster data acquisition without sacrificing data quality, as compared with stepscan imaging. This approach to data collection introduces some unique peculiarities to the acquisition and processing of imaging data. The purpose of this paper is to address a few of these concerns in terms of their effect on final data quality. Also, the practical aspects of implementing such an acquisition scheme are described in detail.

High-throughput heterogeneous catalytic science.

High-throughput experimentation in heterogeneous catalysis has recently experienced nearly exponential growth. Initial qualitative screening has evolved into quantitative high-throughput experimentation, characterization, and analysis. This allows high-throughput catalysis now to rise above simple screening to the level of fundamental understanding of reaction mechanisms, which will lead on a faster path to the Holy Grail of catalysis: rational catalyst design.

Performance and application of a new planar array infrared spectrograph operating in the mid-infrared (2000-975 cm(-1)) fingerprint region.

A no-moving-part planar array infrared spectrograph (PA-IR) equipped with a 256 x 256 mercury cadmium telluride (MCT) focal plane array has been designed and constructed. The performance of the instrument, whose frequency range extends from 2000-975 cm(-1), has been assessed in terms of resolution, bandwidth, and signal-to-noise ratio. The PA-IR spectrograph is able to record spectra with an 8.7 ms time resolution and has peak-to-peak noise levels as low as 2.4 x 10(-4) A.U. As a demonstration of the potential of PA-IR, the dynamics of reorientation of a liquid crystalline sample exposed to a single electric field pulse has been studied. It was shown that PA-IR can be used for the simultaneous acquisition of two orthogonally polarized spectra. The advantages and limitations of PA-IR, step-scan Fourier transform infrared (FT-IR), and ultrarapid-scanning FT-IR for real-time studies of reversible and irreversible phenomena are thoroughly discussed.

Acquisition of mid-infrared spectra from nonrepeatable events with sub-100-micros temporal resolution using planar array infrared spectroscopy.

A novel method is presented that is capable of collecting time-resolved vibrational spectroscopic information with sub-100-micros temporal resolution. Unlike previous step scan FT-IR approaches, the phenomena under study do not necessarily need to be repeatable. The methodology described herein is based on the planar array infrared (PA-IR) technique, which utilizes a spectrograph for wavelength dispersion and a mid-infrared focal plane array (FPA) detector for simultaneous detection of multiple wavelengths. Unlike previous PA-IR approaches, a rolling mode FPA is employed. This unique data readout mode, where data are read out of the array two rows at a time, is exploited to generate increased temporal resolution. The capabilities of this technique are demonstrated using the example of the electric field-induced Freedericksz transition of a nematic liquid crystal. It is shown that the orientational dynamics of a single transition can be tracked over a spectral range of 154 cm(-)(1) with a temporal resolution of 99.17 micros while requiring a total experimental time of less than 1 s.