Dual pH‐ and temperature‐responsive hydrogels with extraordinary swelling/deswelling behavior and enhanced mechanical performances

Abstract

pH-and temperature-responsive semi-interpenetrating nanocomposite hydrogels (NC hydrogels) were prepared with surface-functionalized graphene oxide (GO) as the crosslinker, N-isopropylacrylamide (NIPAM) as the monomer, and chitosan (CS) as an additive. The effects of 3-(trimethoxysilyl)propylmethacrylate-modified GO sheets and CS content on various physical properties were investigated. Results show that PNIPAM/CS/GO hydrogels undergo a large volumetric change in response to temperature. Swelling ratios of PNIPAM/CS/GO hydrogels are much larger than those of the conventional organically crosslinked PNIPAM hydrogels. The deswelling test indicates that the deswelling rate was greatly enhanced by incorporating CS into the hydrogel network and using the surface-functionalized GO as the crosslinker. The pH-sensitivity of PNIPAM/CS/GO hydrogels is evident below their volume phase transition temperature. Moreover, the PNIPAM/CS/GO hydrogels have a much better mechanical property compared with traditional hydrogels even in a high water content of 90%.

Synthesis and characterization of thermally responsive N-isopropylacrylamide hydrogels copolymerized with novel hydrophobic polyphenolic crosslinkers

“…The overall hydrophilic content was decreased, and less hydrogen bonds were formed thus lower temperature was needed to break the bonds. The LCST could either be decreased by incorporation of hydrophobic components or increased by addition of hydrophilic components [47, 48]. …”

Temperature responsive polymer brushes grafted from graphene oxide: an efficient fluorescent sensing platform for 2,4,6-trinitrophenol

“…Among these new bands, the characteristic peak at 1646 cm -1 is assigned to the existence of the carbonyl stretching vibration of the esters, and the others are the characteristic vibrations of the grafted RAFT agent. 34 After the block copolymerization, a new typical peak appears at 906 cm -1 which is the characteristic peak of GMA units (see Fig.1d), and the obvious enhancement of the peak of ester carbonyl groups accompanied with red shift (1725 cm -1 ), indicating that the second block of P(GMA-co-MQ) with more ester carbonyl groups is attached on the surface of GO. For the spectrum of GPNM (Fig.1c), some new vibration peaks could be observed at 1654, 2800 and 3000 cm -1 .…”

A robust double-network hydrogel with under sea water superoleophobicity fabricated via one-pot, one-step reaction

“…However, the applications of hydrogels are often limited by their mechanical behaviors [11], such as low mechanical strength, poor toughness, limited recoverability, which are mostly because of their intrinsic structure heterogeneity and the lack of efficient energydissipation mechanism [12]. Many efforts had been performed to develop new polymerization processes for synthesizing strong and flexible hydrogels with special structures [13][14][15][16][17][18]. Among all these strategies, double network (DN) hydrogels consisted of two independent crosslinked polymer networks have been demonstrated the improved mechanical properties compared to the traditional ones.…”

“…The prepared PAMPS/PAAm DN hydrogels exhibited well fracture strength as high as several tens of megapascals. Huang has also found a pH-and temperature-responsive DN hydrogel which was prepared by using poly (N-isopropyla-crylamide) as the first network, polyacrylic acid as the second network [14]. However, in their works [13,14] when the first single network hydrogel was immersed into the second component solution to form the second network, the volume swelling was much larger than before immersion and made it difficult to form various desirable shapes.…”

“…Huang has also found a pH-and temperature-responsive DN hydrogel which was prepared by using poly (N-isopropyla-crylamide) as the first network, polyacrylic acid as the second network [14]. However, in their works [13,14] when the first single network hydrogel was immersed into the second component solution to form the second network, the volume swelling was much larger than before immersion and made it difficult to form various desirable shapes. To overcome these shortages, the brittle first network hydrogelswere roughly grinded into small particles with size of several tens of micrometers, and then these particles were immersed into the second component aqueous solution for forming a DN hydrogels [19].…”