Poly(N-isopropylacrylamide)–clay based hydrogels controlled by the initiating conditions: evolution of structure and gel formation

Abstract

The formation of the hydrogel poly(N-isopropylacrylamide)-clay (LAPONITE®) by redox polymerization was investigated, and the main factors governing the gel build-up were determined. The significant effect of the redox initiating system ammonium peroxodisulfate (APS) and tetramethylethylenediamine (TEMED) on gel formation and structure was established, making it possible to control the structure of the gel. Moreover, the pre-reaction stage involving the quality of the clay exfoliation in an aqueous suspension and the interaction of reaction components with the clay play a role in controlling the polymerization and gel structure. The molecular and phase structure evolution during polymerization was followed in situ by the following independent techniques: Fourier transform infrared spectroscopy (FTIR), chemorheology, small-angle X-ray scattering (SAXS) and ultraviolet-visible spectroscopy (UV/Vis). The combination of these methods enabled us to describe in detail particular progress stages during the gel formation and determine the correlation of the corresponding processes on a time and conversion scale. The mechanism of gel formation was refined based on these experimental results.

X10 expansion microscopy enables 25‐nm resolution on conventional microscopes

“…Primary TEMED, sulfate, and hydroxyl radicals are generated by redox initiation with KPS and TEMED 37.…”

Topological Insight into Superabsorbent Hydrogel Network Structures: a 1H Double‐Quantum NMR Study

“…Since the inhomogeneity of polymer gels is closely related to spatial concentration fluctuations, it has been investigated with scattering methods such as light scattering, small‐angle X‐ray and neutron scattering, or by a combination of both . Several spectroscopy techniques such as nuclear magnetic resonance (NMR), ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy have been utilized to study the molecular and phase evolution during formation of hydrogels . Among them, especially proton double‐quantum ( 1 H DQ) NMR has become one of the most powerful and quantitative methods .…”

“…[21,[26][27][28] Several spectroscopy techniques such as nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy have been utilized to study the molecular and phase evolution during formation of hydrogels. [29,30] Among them, especially proton double-quantum ( 1 H DQ) NMR has become one of the most powerful and quantitative methods. [31][32][33][34][35] It addresses the 1 H-1 H dipolar couplings, which depend on the orientation of chain segments, i.e., geometry, distance, and chain dynamics.…”

Effect of sodium hydroxide solution as polymerization solvent and activator on structural, mechanical and antibacterial properties of PNIPAAm and P(NIPAAm–clay) hydrogels

“…As to the results reported by Haraguchi et al, radicals produced by redox initiator pairs are concentrated near the surfaces of the clay layers. After initiation of NIPAAm polymerization, propagating PNIPAAm chains start to tie neighboring clay layers while Matejka et al reported that in the case of TEMED‐APS pair as redox initiator, spectroscopic characterization results proved that the interactions between TEMED molecules and clay layers were much stronger than clay‐NIPAAm and clay‐PNIPAAm interactions . Okano et al reported that the incorporation of hydroxyl end groups to PNIPAAm chains, i.e., the terminal hydrophilic modification was more effective to raise the LCST compared with their random copolymers with hydrophilic comonomers, due to strong hydrogen bonds of their free ends with water molecules .…”