Development of visible-light responsive and mechanically enhanced “smart” UCST interpenetrating network hydrogels

Abstract

An interpenetrating polymer network (IPN), chlorophyllin-incorporated environmentally responsive hydrogel was synthesized and exhibited the following features: enhanced mechanical properties, upper critical solution temperature (UCST) swelling behavior, and promising visible-light responsiveness. Poor mechanical properties are known challenges for hydrogel-based materials. By forming an interpenetrating network between polyacrylamide (PAAm) and poly(acrylic acid) (PAAc) polymer networks, the mechanical properties of the synthesized IPN hydrogels were significantly improved compared to hydrogels made of a single network of each polymer. The formation of the interpenetrating network was confirmed by Fourier Transform Infrared Spectroscopy (FTIR), the analysis of glass transition temperature, and a unique UCST responsive swelling behavior, which is in contrast to the more prevalent lower critical solution temperature (LCST) behaviour of environmentally responsive hydrogels. The visible-light responsiveness of the synthesized hydrogel also demonstrated a positive swelling behavior, and the effect of incorporating chlorophyllin as the chromophore unit was observed to reduce the average pore size and further enhance the mechanical properties of the hydrogel. This interpenetrating network system shows potential to serve as a new route in developing "smart" hydrogels using visible-light as a simple, inexpensive, and remotely controllable stimulus.

Hydrogels as dynamic memory with forgetting ability

“…These gels, also showing an asymmetric swelling/shrinking behavior (26,35), in principle, can act as dynamic memory but only working at their critical temperatures. Moreover, the large volume change (tens or hundreds of times in volume) at the critical temperature (36,37) brings difficulty to construct memory devices.…”

Thermo‐ and CO2‐triggered swelling polymer microgels for reducing water‐cut during CO2 flooding

“…It is known that the solubility of the sulfobetaine polymers in solutions depends on the various intermolecular and intramolecular pairing zwitterionic association of the inner salt moieties with ion pair. pSBMA, for instance, often represents typical UCST in aqueous solutions . At low temperature, in the absence of electrolyte, interattraction and intraattraction caused by electrostatic effect would hinder chains from dissociation within, so that the incorporated moieties prevent dissolution of the polymer in the water.…”

A comparative study of tough hydrogen bonding dissipating hydrogels made with different network structures

“…For the pure PAAm FTIR spectra, the peaks at 1603 cm À1 and 1645 cm À1 were assigned to the N-H bending and C]O stretching of the amide group. 35 In the PAA spectrum, the peaks at 1234 cm À1 and 1695 cm À1 were attributed to the C-O stretch and C]O stretch of the carboxylic acid group. 35 The FTIR spectrum of PAAm LC - PAA-2 showed signatures of both the PAA and PAAm, which conrmed the incorporation of PAA inside the PAAm gel (Fig.…”

“…33 The carboxylic acid groups of PAA serve as hydrogen bond donors, while the amide groups of PAAm serve as hydrogen bond acceptors. 34,35 Tannic acid, a polyphenol capable of UV-polymerization, with multiple hydrogen bonding donor sites, was chosen as the second type of hydrogen bonding network. Aer polymerization, tannic acid is expected to form short, branched polymers (as compared to the long linear poly(acrylic acid)).…”