Analyzing the Water Confined in Hydrogel Using Near-Infrared Spectroscopy

Abstract

Analysis of the confined water in hydrogels is essential for understanding the chemical and physical properties. Methods to quantify the content and study the structure of water in hydrogel using near-infrared (NIR) spectroscopy were proposed. The NIR spectra of poly-N,N,-dimethylacrylamide (PDMAA) hydrogel with different water contents were measured at different temperatures. A partial least squares (PLS) model was established using the spectra of the samples with water content (wh) from 4.0% to 387.6%. Continuous wavelet transform (CWT) was adopt to calculate the resolution enhanced spectra, from which the spectral features of water species with free OH (S0) and with one or two hydrogen bonds (S1, S2) was obtained. The variation of these water species with water content suggests the existence of the water molecules bonding to NH groups by one hydrogen bond (S1NH), the water-cage directly hydrating the CH groups of the polymer network and bulk-like water. Moreover, the variation of water structures with temperature shows that the release of bulk-like water occurs in the phase transition of the hydrogel, but the S1NH and cage water keep unchanged. The former explains the sudden volume shrinkage for the phase transition and the latter may be the reason for the shape memory effect in the repeated swelling and deswelling of hydrogels.

Pectin self-assembly and its disruption by water: insights into plant cell wall mechanics

“…The relative amounts of H-bonded water molecules and protonated water clusters is known to play a significant role in the rehydration characteristics of dehydrated hydrogels. 29…”

“…The relative amounts of H-bonded water molecules and protonated water clusters is known to play a significant role in the rehydration characteristics of dehydrated hydrogels. 29 Upon rehydration from different extents of dehydration, the water configurations do not reverse to their initial state. This is evident from the aquagram patterns (Fig.…”

Wavelet Transform Makes Water an Outstanding Near-Infrared Spectroscopic Probe

“…For studying the water structures in a confinement environment, water in hydrogels and reverse micelles (RMs) were analyzed by NIR spectroscopy [76,77]. CWT was also adopted to enhance the resolution.…”

Simultaneous Rapid Detection of Multiple Physicochemical Properties of Jet Fuel Using Near-Infrared Spectroscopy

“…By combining chemometric algorithms, a rapid detection model can be established between the spectra and target properties, thus enabling the qualitative or quantitative analysis of samples. − NIR spectroscopy is highly efficient, rapid, and nondestructive and can simultaneously determine multiple components. It has been widely applied in various industries, such as chemical engineering, agriculture, and medicine. − In recent years, researchers have applied NIR spectroscopy to the characterization and quality detection of jet fuels. By utilizing NIR spectroscopy in conjunction with chemometrics, multivariate regression models have been constructed to rapidly detect the physicochemical properties of jet fuels. − Xiao et al developed a rapid analysis model for the total acid value of jet fuel based on NIR spectroscopy using a backpropagation neural network (BP-ANN) and partial least-squares (PLS) regression methods.…”