The evaluation of temperature and pH influences on equilibrium swelling of poly(n-isopropylacrylamide-co-acrylic acid) hydrogels

Abstract

Hydrogels are synthesized by the method of radical polymerization of monomers: N-isopropylacrylamide (NIPAM) and acrylic acid (AA). Characterization of poly(N-isopropylacrylamide-co-acrylic acid) hydrogels, p(NIPAM/AA), has been performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and by determination of the swelling behaviour in aqueous solutions at different temperatures (25, 31 and 37 °C) and pH values (2.2, 4.5, 6 and 6.8). After lyophilisation in the solution at pH 6 and temperature of 25 °C, p(NIPAM/AA) hydrogels have rapidly reached equilibrium degree of swelling, α e , in comparison to non-lyophilized samples. The mechanism of solvent transport within matrix in lyophilized samples corresponds to less Fickian diffusion, whereas Super case II diffusion is characteristic for non-lyophilized samples. p(NIPAM/AA) hydrogel with 1.5 mol% of ethylene glycol dimethacrylate (EGDM) at the temperature of 25 °C and pH 6.8, has reached the highest swelling equilibrium degree, α e = 259.8. The results of swelling studies have shown that p(NIPAM/AA) hydrogels can be classified as superabsorbent polymers (SAPs). For the evaluation of pH and temperature influences on synthesized hydrogels swelling, a full three-level experimental design has been used. Two-factor interaction model (2FI) is the most optimal model of a full three-level experimental design for representing the swelling equilibrium degree of p(NIPAM/AA) hydrogels as a function of investigated parameters, i.e., temperature and pH.

Synthesis and characterization of poly(N-isopropylmethacrylamide-co-N-isopropylacrylamide) copolymers

“…2b), the characteristic absorption band of strong intensity is at the maximum of 3295 cm -1 , which is assigned to valence vibrations of the secondary amino-group, ν(N-H) [41] and the absorption band at 3073 cm -1 , which is a result of asymmetric vibrations of the vinyl group, νas(=C-H). Absorption bands with the maxima at 2971 cm -1 and 2876 cm -1 in the NIPAM FTIR spectrum are the result of asymmetric and symmetric valence vibrations of the C-H bond in the methyl group, respectively [42]. A medium intensity absorption band with the maximum at 2934 cm -1 originates from asymmetric valence vibrations of the C-H bond in the NIPAM isopropyl group, νas(C-H).…”

“…The result of C=C bond vibrations is a strong intensity absorption band with the maximum at 1619 cm -1 [45]. A medium intensity absorption band at 1371 cm -1 corresponds to deformation vibrations in the plane of C-H bond from the NIPAM isopropyl group, δ(C-H) [42]. Evidence of the existence of an isopropyl group in the structure of NIPAM is a strong intensity absorption band with two maxima at 1167 and 1130 cm -1 .…”

Polymer/zeolite nano-composite hydrogels as promising water reservoir materials: effect of clinoptilolite content on physicochemical properties

“…Due to the weak physical and mechanical properties of the natural polymer based hydrogels, simultaneous application of natural and synthesized polymers in hydrogels' structure has been developed. Simultaneous application of natural and synthesized polymers in preparation of hydrogels, not only resolve the mechanical issues, but also it leads to achieve biocompatible hydrogel products [27,28]. So, synthesizing the hydrogels with semi-IPN structure, using both natural and synthetic polymers and by adding proper additives can lead to achieve a proper hydrogel system with desired properties.…”

Hydrogels based on N-isopropylmethacrylamide and N-isopropylacrylamide

“…Superabsorbent hydrogels are gels with the capacity of absorbing 100 times higher than the xerogel weight [55]. Hydrogels with superabsorbent properties are synthesized through radical polymerization from the NIPAM and AA monomers, as presented in the paper of Zdravković et al poly(NIPAM-co-AA) hydrogels demonstrate pH sensitivity whereupon the equilibrium swelling degree increases from 8.3 to 259.8 with the rise in pH values from 2.2 to 6.8 [56]. The absorption capacity of hydrogels can be used for concentrating solutions of different compounds, i.e.…”