We used two-dimensional (2D) correlation infrared spectroscopy to study further the potassium-induced conformation transition in Nephila spidroin films. It provided increased resolution and important new information on the sequence of events in the conformation transition process, showing that â-sheet formed from the helical component before they formed from random coil. It also showed more evidence that formation of the 1691cm-1 (turn/bend) peak did not proceed with the same kinetics as the 1620cm-1 (antiparallel â-sheet component) one, so we attribute the 1691cm-1 peak to turns which formed with different kinetics as the antiparallel β-sheets. We present a single coherent and detailed hypothesis for the assembly and secondary structural transition of silk proteins in vivo and in vitro based on our findings and on evidence from other laboratories.

In this study, the diffusion process of water molecules in poly(є-caprolactone) (PCL) has been investigated using in-situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In our system, the original broad water OH bands in 1D IR spectra can be effectively differentiated into four bands, located at 3641, 3593, 3410, and 3203cm-1, respectively, using 2D correlation analysis. The bands at 3641cm-1 (antisymmetric) and 3593cm-1 (symmetric) are assigned to the OH stretching vibration of water partially hydrogen bonded with hydrophilic carbonyl group (CvO) of PCL, while the other band pair at 3410cm-1 (antisymmetric) and 3203cm-1 (symmetric) could be attributed to the stretching vibration of water fully hydrogen bonded with another water molecule. According to the result of the asynchronous correlation, it was concluded that the water molecules at first diffuse into free volume (microvoids) or are molecularly dispersed into the PCL matrix and then form hydrogen bond with the CvO group of the polymer during the process of water diffusion. In addition, the diffusion coefficient was estimated using nonlinear curve fitting of OH band areas in the range of 3800-3000cm-1.

In the present contribution, two-dimensional ATR-FTIR spectroscopy was used to study the diffusion of water in poly(-caprolactone) (PCL). In the spectral region of the

Two-dimensional (2D) correlation ATR-FTIR spectroscopy was used to study the dynamic diffusion behavior and state of water in syndiotactic polypropylene (S-PP). The 2D asynchronous spectra of water bending band clearly reveal that there are three separate bands in the 1800-1500cm-1 region. These three bands at 1676, 1645, and 1592cm-1 are assigned, respectively, to the aggregated water with strong hydrogen bond, the aggregated water with moderate strong hydrogen bond, and the "free water". On the basis of this approach, the following mechanism for the diffusion process of water in S-PP has been proposed: the aggregated water molecules first diffuse into the polymer during the diffusion process. The water molecules with strong hydrogen bond will diffuse slower than water with moderate strong hydrogen bond because of their large size. In the late stage of the diffusion process, some aggregated water molecules in the PP matrix are forced to dissolve into the "free water" form.

The diffusion of different deuterium-labeled (OD) low-molecular-weight alcohols and D2O in Nylon 11 has been investigated by monitoring the NH/ND exchange in the polymer by Fourier transform near-infrared (FTNIR) spectroscopy. The results demonstrate that the diffusion process of the different penetrants is strongly controlled by their molecular structure and geometry. To characterize this phenomenon quantitatively, the diffusion coefficients for the different deuteration agents have been determined for Nylon 11. The rate of the diffusion was found to decrease with increasing size of alcohol. Furthermore, it could be shown that with this technique the less ordered regions of the polymer can be separated spectroscopically from the crystalline domains, which are not accessible for the isotopically labeled diffusants.