Exchange Counterion in Polycationic Hydrogels: Tunability of Hydrophobicity, Water State, and Floating Capability for a Floating pH Device

Abstract

Smart gel materials are capable of controlling and switching swelling, water state, and wettability properties triggered by external stimuli. In this study, we fabricated a series of polyelectrolyte hydrogels bearing a 3-trimethylammoniumpropyl pendant to a methacrylamide-based backbone and examined the switchability with hydrophobic-like counteranions. The exchange between the initial chloride and camphor sulfate (CaS), dodecyl sulfate (DS), and perfluorooctanoate (PFO) counterions was investigated. The kinetics of the exchange showed that the fast exchange (within 4 h) of PFO allowed for a favorable coordination for ion pairing, resulting in a decrease in hydration. The reversibility of the exchange to the Cl- ion was only enabled for the CaS ion due to its bulkiness, while the PFO and DS hydrogels were unable to exchange, even by using tetrabutylammonium chloride, which is a structurally similar reagent, due to aggregation or the coagulates in the collapsed state of the linear tails of the counterions. The hydrogels exhibited a modulable water state and water swelling. Moreover, the hydrogels containing DS and PFO, as counterions, showed surface hydrophobic (contact angle 90°) and high hydrophobic (110°) behavior, respectively. The Raman spectrometry fluorescence with a pyrene probe indicated an increase in strong hydrogen-bonded water molecules, water confinement, and hydrophobic domains in the PFO hydrogel. Moreover, the PFO-modified hydrogel demonstrated a free-floating ability on the water surface, with a strong water repellency, showing that it has the potential to be applied in a floating pH detection device to distinguish between volatile and nonvolatile bases in a controlled manner.

Effect of Magnetized Coagulants on Wastewater Treatment: Rice Starch and Chitosan Ratios Evaluation

“…Off-plane bending –OH vibrations are also recorded at 680 cm −1 . In general, the FTIR spectra of chitosan show discrete bands corresponding to amide groups between 1305 and 1660 cm −1 [ 65 , 66 ], N-H peaks, and hydrogen-bonded hydroxyl groups between 3270 and 3800 cm −1 [ 67 ]. The FTIR spectra of RS and its magnetic coagulants ( Figure 5 b) revealed a particularly strong peak at about 995 cm −1 , which was attributed to the C–O of starch’s C–O–C bonds [ 68 ].…”

Electro-Chemical Actuation of Nanoporous Metal Materials Induced by Surface Stress

“…For the actuation of an electrolyte-free system, the dimensional changes in the nanoporous metal/polymer composite still originate from the surface stress of the nanoporous metal [33]. The surface stress in this system is modulated by the co-adsorbed sulfate counterions that are presented in the doped polymer chains coating matrix upon application of an external potential [9,19,34,35].…”

Modeling Tunable Fracture in Hydrogel Shell Structures for Biomedical Applications

“…For example, Bratskaya et al [ 72 ] discussed the applicability of a stimuli-responsive hydrogel of tunable dissolution rate under physiological conditions. Similarly, Danko et al [ 73 ] prepared a polyelectrolyte hydrogel, the swelling and water state of which can be controlled by external stimulation. Their hydrogel shows a capability of free-floating on the water surface, indicating its potential use in floating pH detection devices.…”