CC BY
11B-O-9
Raman characterization of aqueous solutions of diols
V.S. Novikov1, K.A. Prokhorov1, P.V. Ivchenko2, E.A. Sagitova1, V.V. Kuzmin1, L.Yu. Ustynyuk2, G.Yu. Nikolaeva1
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov Str. 38, 119991 Moscow,
Russia
2-Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory 1-3, 119991 Moscow,
Russia
Aqueous solutions of ethylene glycol (EG, HO-CH2-CH2-OH) and 1,3-propylene glycol (1,3-PG, HO-CH2-CH2-CH2-OH) are widely used as antifreezes in numerous applications. The relative contents of the diol and water determine the structure and physicochemical properties of the solutions, including the freezing point. Raman spectroscopy is an effective tool to evaluate the chemical composition and conformational order, and to characterize the intermolecular interactions of these polar molecules. The aims of this work were comparative Raman study of aqueous solutions of EG and 1,3-PG and the elaboration of Raman methods for their structural characterization.
T3
<u .N
E
0% EG 10% EG 20% EG 30% EG 40% EG 50% EG 60% EG 70% EG 80% EG 90% EG 100% EG
2600 2800 3000 3200 3400 3600 3800 4000
b
Wavenumber, cm
-1
Cwater /Cdiol
a
0
2
4
6
8
0
Figure 1. Raman spectra of aqueous solutions of EG with various EG mole contents (a) and ratios of the intensities of the OH stretching band and the selected diol reference bands (the EG band at 2880 cm-1 or the 1,3-PG band at 2920 cm-1) (b).
The Raman spectra of EG, 1,3-PG and water contain the O-H stretching band, extended from 2800 to 3800 cm-1. Intensity of this band in the Raman spectra of aqueous solutions (Figure 1a) depends strongly on the diol content. We found out that the ratios of the intensities of the OH stretching band and the selected reference diol bands are the linear functions of the ratio of the contents of the solution components (Figure 1b) and, thus, can be used to evaluate the chemical compositions of these binary solutions.
Changes of the solution Raman spectra in the fingerprint region were insignificant in the full range of the diol concentrations. In particular, the diol bands at about 800 cm-1, which are the markers of gauche-conformers in the O-C-C-O and O-C-C-C-O backbones of the diols [1], have similar intensities and peak positions independent on the diol concentration. Thus, there are no noticeable changes in the diol conformational compositions with dissolving in water.
This work was funded by the Russian Foundation for Basic Research (project No. 19-02-00931). We are grateful to the Joint Supercomputer Center of the RAS for the possibility of using their computational resources for our calculations.
[1] V.V. Kuzmin, V.S. Novikov, E.A. Sagitova, L.Y. Ustynyuk, K.A. Prokhorov, P.V. Ivchenko, G.Y. Nikolaeva, Correlations among the Raman spectra and the conformational compositions of ethylene glycol, 1,2- and 1,3-propylene glycols, J. Mol. Struct. (2021) 130847. https://doi.org/10.1016/j.molstruc.2021.130847.
