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Polyampholyte gels, which have hierarchical structures, exhibit excellent self-healing properties and have great promise for biomaterials and bioengineering. We investigated the relationship between microscopic structures and macroscopic viscoelastic properties of polyampholyte gels and found three factors influencing their viscoelastic properties, including the chemical crosslinking bonds, topological entanglements controlled by monomer concentration, and the ionic bonds. Ionic strength plays a major role on the strength of ionic bonds. A crossover point of elastic modulus and loss modulus was observed in the dynamic frequency sweeps at low monomer concentration or low chemical crosslinking density for gels with intermediate strength of ionic bonds. The solid-liquid transition signaled by the crossover point is a typical feature of dynamic associated gels, representing the dynamical association-dissociation of the ionic bonds and full relaxation of the topological entanglements in the gel network. While the crossover point disappears when the ionic bonds are too weak or too strong to form "permanent" bonds. Consistently, in the non-linear yielding measurement, gels with intermediate strength of the ionic bonds are ductile and yield at very large shear strain due to the self-healing properties and the dynamic association-dissociation of the ionic bonds. But the self-healing properties disappear when the ionic bond strength is too weak or too strong. Our work reveals the mechanism of how the dynamic association-dissociation of ionic bonds influences both the linear and non-linear viscoelastic properties of the polyampholyte gels. [ABSTRACT FROM AUTHOR]

Polyampholyte (PA) hydrogels are randomly copolymerized from anionic and cationic monomers, showing good mechanical properties owing to the existence of numerous ionic bonds in the networks. However, relatively tough PA gels can be synthesized successfully only at high monomer concentrations (CM), where relatively strong chain entanglements exist to stabilize the primary supramolecular networks. This study aims to toughen weak PA gels with relatively weak primary topological entanglements (at relatively low CM) via a secondary equilibrium approach. According to this approach, an as-prepared PA gel is first dialyzed in a FeCl3 solution to reach a swelling equilibrium and then dialyzed in sufficient deionized water to remove excess free ions to achieve a new equilibrium, resulting in the modified PA gels. It is proved that the modified PA gels are eventually constructed by both ionic and metal coordination bonds, which could synergistically enhance the chain interactions and enable the network toughening. Systematic studies indicate that both CM and FeCl3 concentration ( C FeCl 3 ) influence the enhancement effectiveness of the modified PA gels, although all the gels could be dramatically enhanced. The mechanical properties of the modified PA gel could be optimized at CM = 2.0 M and C FeCl 3 = 0.3 M, where the Young's modulus, tensile fracture strength, and work of tension are improved by 1800%, 600%, and 820%, respectively, comparing to these of the original PA gel. By selecting a different PA gel system and diverse metal ions (i.e., Al3+, Mg2+, Ca2+), we further prove that the proposed approach is generally appliable. A theoretical model is used to understand the toughening mechanism. This work well extends the simple yet general approach for the toughening of weak PA gels with relatively weak chain entanglements. [ABSTRACT FROM AUTHOR]

Hydrogels with high mechanical strength, good crack resistance, and good adhesion are highly desirable in various areas, such as soft electronics and wound dressing. Yet, these properties are usually mutually exclusive, so achieving such hydrogels is difficult. Herein, we fabricate a series of strong, tough, and adhesive composite hydrogels from polyampholyte (PA) gel reinforced by nonwoven cellulose-based fiber fabric (CF) via a simple composite strategy. In this strategy, CF could form a good interface with the relatively tough PA gel matrix, providing high load-bearing capability and good crack resistance for the composite gels. The relatively soft, sticky PA gel matrix could also provide a large effective contact area to achieve good adhesion. The effect of CF content on the mechanical and adhesion properties of composite gels is systematically studied. The optimized composite gel possesses 35.2 MPa of Young's modulus, 4.3 MPa of tensile strength, 8.1 kJ m−2 of tearing energy, 943 kPa of self-adhesive strength, and 1.4 kJ m−2 of self-adhesive energy, which is 22.1, 2.3, 1.8, 6.0, and 4.2 times those of the gel matrix, respectively. The samples could also form good adhesion to diverse substrates. This work opens a simple route for fabricating strong, tough, and adhesive hydrogels. [ABSTRACT FROM AUTHOR]

Polyampholyte (PA) hydrogels are randomly copolymerized from anionic and cationic monomers, showing good mechanical properties owing to the existence of numerous ionic bonds in the networks. However, relatively tough PA gels can be synthesized successfully only at high monomer concentrations (CM), where relatively strong chain entanglements exist to stabilize the primary supramolecular networks. This study aims to toughen weak PA gels with relatively weak primary topological entanglements (at relatively low CM) via a secondary equilibrium approach. According to this approach, an as-prepared PA gel is first dialyzed in a FeCl3 solution to reach a swelling equilibrium and then dialyzed in sufficient deionized water to remove excess free ions to achieve a new equilibrium, resulting in the modified PA gels. It is proved that the modified PA gels are eventually constructed by both ionic and metal coordination bonds, which could synergistically enhance the chain interactions and enable the network toughening. Systematic studies indicate that both CM and FeCl3 concentration (CFeCl3) influence the enhancement effectiveness of the modified PA gels, although all the gels could be dramatically enhanced. The mechanical properties of the modified PA gel could be optimized at CM = 2.0 M and CFeCl3 = 0.3 M, where the Young’s modulus, tensile fracture strength, and work of tension are improved by 1800%, 600%, and 820%, respectively, comparing to these of the original PA gel. By selecting a different PA gel system and diverse metal ions (i.e., Al3+, Mg2+, Ca2+), we further prove that the proposed approach is generally appliable. A theoretical model is used to understand the toughening mechanism. This work well extends the simple yet general approach for the toughening of weak PA gels with relatively weak chain entanglements.

With increasing global energy consumption, oil/gas drilling has gradually expanded from conventional shallow reservoirs to deep and ultra-deep reservoirs. However, the harsh geological features including high temperature and high salinity in ultra-deep reservoirs have become a critical challenge faced by water-based drilling fluids (WDFs), which seriously deteriorate the rheology and fluid loss properties, causing drilling accidents, such as wellbore instability and formation collapse. In this study, a novel temperature- and salt-resistant micro-crosslinked polyampholyte gel was synthesized using N,N-dimethylacrylamide, diallyldimethyl ammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid, maleic anhydride and chemical crosslinking agent triallylamine through free radical copolymerization. Due to the synergistic effect of covalent micro-crosslinking and the reverse polyelectrolyte effect of amphoteric polymers, the copolymer-based drilling fluids exhibit outstanding rheological and filtration properties even after aging at high temperatures (up to 200 °C) and high salinity (saturated salt) environments. In addition, the zeta potential and particle size distribution of copolymer-based drilling fluids further confirmed that the copolymer can greatly improve the stability of the base fluid suspension, which is important for reducing the fluid-loss volume of WDFs. Therefore, this work will point out a new direction for the development of temperature- and salt-resistant drilling fluid treatment agents. [ABSTRACT FROM AUTHOR]

Hydrogels with high mechanical strength, good crack resistance, and good adhesion are highly desirable in various areas, such as soft electronics and wound dressing. Yet, these properties are usually mutually exclusive, so achieving such hydrogels is difficult. Herein, we fabricate a series of strong, tough, and adhesive composite hydrogels from polyampholyte (PA) gel reinforced by nonwoven cellulose-based fiber fabric (CF) via a simple composite strategy. In this strategy, CF could form a good interface with the relatively tough PA gel matrix, providing high load-bearing capability and good crack resistance for the composite gels. The relatively soft, sticky PA gel matrix could also provide a large effective contact area to achieve good adhesion. The effect of CF content on the mechanical and adhesion properties of composite gels is systematically studied. The optimized composite gel possesses 35.2 MPa of Young’s modulus, 4.3 MPa of tensile strength, 8.1 kJ m−2 of tearing energy, 943 kPa of self-adhesive strength, and 1.4 kJ m−2 of self-adhesive energy, which is 22.1, 2.3, 1.8, 6.0, and 4.2 times those of the gel matrix, respectively. The samples could also form good adhesion to diverse substrates. This work opens a simple route for fabricating strong, tough, and adhesive hydrogels.

With increasing global energy consumption, oil/gas drilling has gradually expanded from conventional shallow reservoirs to deep and ultra-deep reservoirs. However, the harsh geological features including high temperature and high salinity in ultra-deep reservoirs have become a critical challenge faced by water-based drilling fluids (WDFs), which seriously deteriorate the rheology and fluid loss properties, causing drilling accidents, such as wellbore instability and formation collapse. In this study, a novel temperature- and salt-resistant micro-crosslinked polyampholyte gel was synthesized using N,N-dimethylacrylamide, diallyldimethyl ammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid, maleic anhydride and chemical crosslinking agent triallylamine through free radical copolymerization. Due to the synergistic effect of covalent micro-crosslinking and the reverse polyelectrolyte effect of amphoteric polymers, the copolymer-based drilling fluids exhibit outstanding rheological and filtration properties even after aging at high temperatures (up to 200 °C) and high salinity (saturated salt) environments. In addition, the zeta potential and particle size distribution of copolymer-based drilling fluids further confirmed that the copolymer can greatly improve the stability of the base fluid suspension, which is important for reducing the fluid-loss volume of WDFs. Therefore, this work will point out a new direction for the development of temperature- and salt-resistant drilling fluid treatment agents.

Abstract: Dual temperature/pH-sensitive polyampholyte gels were developed for use as adsorbents and carriers that deal with organic electrolytes such as proteins. NIPA-co-DMAPAA-co-AA gels were prepared by copolymerizing N-isopropylacrylamide (NIPA) as a thermosensitive component with N,N-dimethylaminopropylacrylamide (DMAPAA) as a weakly-basic cation-comonomer, acrylic acid (AA) as a weakly-acidic anion-comonomer, and N,N′-methylenebisacrylamide (MBAA) as a cross-linker, and their thermosensitive and pH-sensitive swelling properties and protein adsorption properties were investigated. The gel adsorbed bovine serum albumin (BSA) applied as a model protein at pH values in the range of 4.5–10 and 25°C as a result of the electrostatic interactions. In addition, the pre-adsorbed BSA was well desorbed from the gel at pH values less than 4 or greater than 11. The pH-sensitivity of the adsorption is found to be based on the protonation of amino groups in DMAPAA and dissociation of carboxyl groups of AA. The BSA adsorption was investigated as a function of MBAA concentration and temperature, and was discussed in terms of the difference in the sizes of the BSA molecule and gel network. [Copyright &y& Elsevier]

In this paper, we first demonstrate the control of the film pore size using neutral hydrophilic 2-hydroxyethyl methacrylate (HEMA) content. To improve the mechanical properties of a polyampholyte (PA), both HEMA and the cross-linker N , N '-methylenebisacrylamide (Bis-Am) were introduced into the PA chain. The predesigned copolymers showed great mechanical properties and optical behavior. The introduction of HEMA significantly increased the water content of the polymer, leading to the formation of porous structures in xerogels. The dynamic interaction between the positive and negative termini of the PA endowed the hydrogels with self-healing ability. The synthesized chemically cross-linked PA gels showed high stability in saline solution. The biocompatibility of the PA gels was confirmed using a cytotoxicity test of cells attached to the synthesized PA-X-2 and PA/HEMA-90/10-X-0.5. The results of this investigation indicate that the synthesized PA gels are applicable as a polymeric scaffold for cell culture.