Phase‐specific Raman analysis of n‐alkane melting by moving‐window two‐dimensional correlation spectroscopy

Abstract

We use moving-window two-dimensional correlation spectroscopy (MW-2DCOS) for phase-specific Raman analysis of the n-alkane (C21H44) during melting from the crystalline solid phase to the intermediate rotator phase and to the amorphous molten phase. In MW-2DCOS, individual peak-to-peak correlation analysis within a small subset of spectra provides both temperature-resolved and spectrally disentangled Raman assignments conducive to understanding phase-specific molecular interactions and chain configurations. We demonstrate that autocorrelation MW-2DCOS can determine the phase transition temperatures with a higher resolving power than commonly-used analysis methods including individual peak intensity analysis or principal component analysis. Besides the enhanced temperature resolving power, we demonstrate that asynchronous 2DCOS near the orthorhombic-to-rotator transition temperature can spectrally resolve the two overlapping peaks embedded in the Raman CH2 twisting band in the orthorhombic phase, which had been only predicted but not observed due to thermal broadening near the melting temperature.

Determining conformational order and crystallinity in polycaprolactone via Raman spectroscopy

“…This transition can be observed and quantified via standard peak fitting techniques,[8] but multivariate analysis techniques such as principal component analysis (PCA) have also been identified as a way to identify peaks sensitive to conformational changes in melting alkanes. [19] PCA has also been used to identify potential hydrogen-bonded chain conformers in poly(acrylic acid) based on subtle changes in the carbonyl stretch region of the Raman spectrum. [20] We thus expect that multivariate analysis techniques like PCA can also separate single-chain effects from crystalline bands in the Raman spectrum of PCL.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…In MW‐2DCOS, individual peak‐to‐peak correlation analysis within a small subset of spectra provides both temperature‐resolved and spectrally disentangled Raman assignments conducive to understanding phase‐specific molecular interactions and chain configurations. They demonstrate that autocorrelation MW‐2DCOS can determine the phase transition temperatures with a higher resolving power than commonly used analytical methods . Liland et al described a model‐based preprocessing in Raman spectroscopy of biological samples.…”

“…They demonstrate that autocorrelation MW-2DCOS can determine the phase transition temperatures with a higher resolving power than commonly used analytical methods. [192] Liland et al described a model-based preprocessing in Raman spectroscopy of biological samples. They demonstrate the basic extended multiplicative signal correction method and some extensions, including a novel shift correction, on real Raman data to demonstrate effects on visual appearance, replicate variation, and prediction.…”

Analysis of temperature‐dependent Raman spectra of minerals: Statistical approaches

“…A number of other approaches to the statistical analysis of vibrational spectral arrays are presented in the literature. There are several works devoted to Two-Dimensional Correlation Spectroscopy (2DCoS) (see, e.g., several studies [23][24][25][26] ). This well-established approach has been successfully applied in Raman, IR spectroscopy, X-ray diffraction, and so forth, when changing the external parameter.…”