The Study of pH Effects on Phase Transition of Multi-Stimuli Responsive P(NiPAAm-co-AAc) Hydrogel Using 2D-COS

Abstract

The temperature and mechanism of phase transition of poly(N-isopropylacrylamide-co-acrylic acid) [P(NiPAAm-co-AAc)], which is one of the multi-stimuli responsive polymers, were investigated at various pHs using infrared (IR) spectroscopy, two-dimensional (2D) gradient mapping, and two-dimensional correlation spectroscopy (2D-COS). The determined phase transition temperature of P(NiPAAm-co-AAc) at pH 4, 3, and 2 based on 2D gradient mapping and principal component analysis (PCA) showed that it decreases with decreasing pH, because COOH group in AAc changes with variation of pH. The results of 2D-COS analysis indicated that the phase transition mechanism of P(NiPAAm-co-AAc) hydrogel at pH4 is different from that at pH2 due to the effect of COOH group of AAc.

A new approach to recognizing the correct pattern of cross-peaks from a noisy 2D asynchronous spectrum by detecting intrinsic symmetry via the Kolmogorov–Smirnov test

“…In the past three decades, numerous application works of 2D-COS, including characterization of intermolecular interactions, have been accumulated in the literature. [16][17][18][19][20][21][22][23][24][25] In these works, crosspeaks in the corresponding 2D correlation spectra serve as a tool to reflect intermolecular interactions. In many cases, nevertheless, interferential cross-peaks irrelevant to intermolecular interactions may also arise in the 2D correlation spectra, which makes cross-peaks unreliable in the investigation of intermolecular interactions.…”

Novel Method for Extracting the Spectrum of a Supramolecular Complex via a Comprehensive Approach Involving Two-Dimensional Correlation Spectroscopy, Genetic Algorithm, and Grid Searching

“…In 2D-COS, a group of spectra, obtained under some form of perturbation on the sample, are converted into a correlation intensity plot defined by two independent spectral variable axes. During the past three decades, 2D-COS has attracted extensive interest and numerous publications have been accumulated. − Many subtle spectral variations, not readily observed in original spectra, can be revealed via the characteristic cross-peaks in the corresponding 2D correlation spectra. Especially, 2D-COS provides a promising chance to investigate intermolecular interactions.…”

A Power Compensation Strategy for Achieving Homogeneous Microstructures for 4D Printing Shape-Adaptive PNIPAM Hydrogels: Out-of-Plane Variations

“…In the meantime, this hydrogel has been reported with various properties when it is co-polymerized with other materials that provide PNIPAM with additional properties. For example, acrylic acid is commonly used as a co-polymer with PNIPAM making the hydrogel pH-responsive [ 38 , 39 , 40 , 41 ]. Moreover, introducing nanoparticles (e.g., gold and ferroferric oxide) into the PNIPAM polymer matrix will make them light-responsive through a photothermal effect when it is exposed to lights with a corresponding wavelength [ 42 , 43 , 44 , 45 ].…”