Polyampholyte Gels Research Articles

Preparation and Characterization of Preformed Polyelectrolyte and Polyampholyte Gel Particles for Plugging of High-Permeability Porous Media.

Excessive reservoir water poses significant challenges in the oil and gas industry by diminishing hydrocarbon recovery efficiency and generating environmental and economic complications. Conventional polymer flooding techniques, although beneficial, often prove inadequate under conditions of elevated temperature and salinity, highlighting the need for more resilient materials. In this research, two types of acrylamide-based preformed particle gels (PPGs) were synthesized, as follows: polyelectrolyte and polyampholyte. These PPGs were engineered to improve plugging efficiency and endure extreme reservoir environments. The polyelectrolyte gels were synthesized using acrylamide (AAm) and sodium acrylate (SA), while the polyampholyte gels incorporated AAm, AMPS, and APTAC, with crosslinking achieved through MBAA. The swelling properties, modulated by temperature, salinity, and pH, were evaluated using the Ritger-Peppas and Yavari-Azizian models. The mechanical characteristics and surface morphology of the gels were analyzed using SEM and BET techniques. In sand pack experiments designed to mimic high-permeability reservoirs, the inclusion of 0.5 wt.% of fine PPGs substantially reduced water permeability, outperforming traditional hydrogels. Notably, the polyampholyte PPGs demonstrated superior resilience and efficacy in plugging. However, the experiments were limited by the low test temperature (25 °C) and brine salinity (26.6 g/L). Future investigations will aim to apply these PPGs in high-temperature, fractured carbonate reservoirs.

Interplay between Microscopic Structures and Macroscopic Viscoelastic Properties of Polyampholyte Gels

Interplay between Microscopic Structures and Macroscopic Viscoelastic Properties of Polyampholyte Gels

Toughening Weak Polyampholyte Hydrogels with Weak Chain Entanglements via a Secondary Equilibrium Approach.

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.

Determination of material parameters in constitutive models using adaptive neural network machine learning

A challenge in the constitutive modeling of time dependent, non-linear solids is the identification of potentially large numbers of material parameters. Here we present an efficient method to determine these parameters using a machine learning algorithm based on Singular Value Decomposition (SVD) and an adaptive neural network (NN). SVD compresses training data and provides outputs for the NN. The trained network rapidly computes the material responses for a large set of material parameters. These responses are then compared with experimental data to determine the optimal parameters. We test our algorithm by performing uniaxial cyclic and relaxation tests on three hydrogels with very different time dependent behaviors: a chemically and physically crosslinked polyampholyte (c-PA) gel; a pure physically crosslinked PA (p-PA) gel, and a Poly(vinylalcohol) (PVA) hydrogel with both chemical and physical crosslinks.

Achieving Swollen yet Strengthened Hydrogels by Reorganizing Multiphase Network Structure

AbstractMany living tissues, such as muscle, become mechanically stronger with growth. Yet, synthetic hydrogels usually exhibit an opposite size‐mechanical property relation, that is, swelling‐weakening behavior. Herein, a series of swollen yet strengthened polyampholyte (PA) hydrogels are developed via a simple metal‐ion solution soaking strategy. In this strategy, a dynamic PA hydrogel (with ionic bonds) is dialyzed in ZrOCl2 solutions (Step‐I) and deionized water (Step‐II) successively to obtain equilibrated hydrogels. Due to the specific Zr4+ ions and PA network structure, Step‐I takes several months with sample size and mechanical performance increasing continuously, while Step‐II only needs several days. Through this strategy, the resultant hydrogel networks are reorganized and eventually constructed by ionic and metalligand bonds, enabling the swelling yet strengthening behavior. A systematic study confirms that dialysis time in Step‐I and corresponding ZrOCl2 concentration can significantly affect the multiphase microstructures of the hydrogels, resulting in different mechanical enhancements. The optimized hydrogel possesses 39.2 MPa of Young's modulus and 3.7 MPa of tensile strength, which are 302 and 5.5 times these of the original PA gel, respectively. Despite distinct swelling, these hydrogels still mechanically surpass many existing high‐performance hydrogels. This study opens a novel pathway for fabricating swollen yet strengthened hydrogels.

Load transfer between permanent and dynamic networks due to stress gradients in nonlinear viscoelastic hydrogels

Relaxation experiments are performed on single edge notch tension (SENT) and T shape specimens consisting of different variations of polyampholyte (PA) hydrogels. These specimens share a common feature of containing regions of high and low stress/strain. This feature enables us to probe the load transfer mechanisms between permanent and dynamic networks of different strengths. This load transfer mechanism is connected to viscoelastic behavior. PA gels are nonlinear viscoelastic, with time-dependent behavior controlled by the breaking and reforming of ionic bonds in the dynamic network. In contrast to the prediction of linear viscoelastic theory, the displacement and strain fields during stress relaxation are not fixed but change with time in a complex way depending on the strength of the dynamic bonds and the observation time window. These experimental results are explained by a nonlinear viscoelastic model. Additional physical insights are gained by appealing to the nonlinear rheology of dynamic bonds or stickers. Our result shows that load transfer between networks can be controlled by modifying the strength of dynamic bonds.

Strong, Tough, and Adhesive Polyampholyte/Natural Fiber Composite Hydrogels.

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.

Strengthening and stiffening in swollen polyampholyte hydrogels

(Size: 5 cm height × 13 cm width). • Developing a modified polyampholyte hydrogel with a swelling-strengthening behavior. • Hydrogel exhibiting high elastic modulus (18.5 MPa) and tensile strength (1.85 MPa). • Providing a simple pathway for achieving strong and stiff swollen hydrogels. Hydrogel networks are usually diluted upon swelling, weakening their mechanical performance. The mechanical weakness limits their practical applications. Herein, we report a modified polyampholyte (PA) hydrogel with a swelling-strengthening behavior via a secondary equilibrium strategy, based on the synergy of ionic and metal–ligand bonds in the network by introducing Zr 4+ ions. Swelling and mechanical properties of the hydrogels are investigated, and the structure–property relationship is discussed. The modified PA gel possesses 18.5 MPa Young’s modulus and 1.85 MPa tensile strength, highly surpassing the original PA gel. This work provides a simple route to achieve strong and stiff swollen hydrogels.

Cryopolymerized Polyampholyte Gel with Antidehydration, Self-Healing, and Shape-Memory Properties for Sustainable and Tunable Sensing Electronics.

Hydrogel-based wearable flexible electronics are attracting tremendous interest for use in human healthcare. However, many of the existing hydrogel electronics are often susceptible to dehydration, leading to weakened stretchability and inaccurate signal extraction. Besides, hydrogels are desired to be much smarter for self-repairing physical damage and enabling performance manipulation. Herein, we develop a kind of cryopolymerized polyampholyte gels with the multifunctionality of antidehydration, self-healing, and shape-memory for wearable sensing electronics. The antidehydration property is enabled by the incorporation of glycerol, endowing the sensing electronics with excellent stretchability and strain-sensing performance in long-term monitoring. The ionic bonds in the polyampholyte gel possess a dynamic feature regulated by alternant NaCl(aq) and H2O treatments, laying the foundation for self-healing and shape-memory. As a result, the sensing electronics can automatically repair physical damages without any sacrifice in sensing performance, after healing both conductivity and strain-sensing performance could return to the initial levels. The shape-memory function enables the temporal adjustment of the initial state of the sensing electronics; both the conductivity and sensing performance, for instance, signal intensity, can be manually manipulated. In all, the cryopolymerized polyampholyte gels with antidehydration, self-healing, and shape-memory properties can be an inspiration to develop sustainable and tunable gel-based electronics for human motion monitoring.

Temperature- and Salt-Resistant Micro-Crosslinked Polyampholyte Gel as Fluid-Loss Additive for Water-Based Drilling Fluids.

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.

Comprehensive evaluation of self-healing polyampholyte gel particles for the severe leakoff control of drilling fluids

Lost circulation has been a serious problem to be solved in many drilling practices during oil, gas and geothermal well drillings. Many materials have been developed and evaluated for the purpose. However, their performance to plug severe leakoff is very limited. Herein, an injectable self-healing hydrogel based on polyampholyte with sulfonated and quaternary ammonium functionalities (P(MPTC-co-NaSS)) was developed and comprehensively evaluated to prevent the severe loss of fluids to formation. By incorporating cation-π (π is for aromatic residues) interaction, the hydrogel shown self-healing property and robustness in severe environment (temperature, salt) by comparison with other hydrogels merely consisting of cation-anion and H-bonding interactions. Aromatic residues enhanced thermal stability above 310 °C. The plugging measurement shown that an addition of 2 wt% dried gel particles can plug high-permeability formation and endure a high pressure of 6 MPa, produce much lower circulation loss and result in a dramatically increased loss volume reduction rate (63.5%) compared with a commercial polymer gel product and an inert material (9.4%) after a self-healing process. Markedly, P(MPTC-co-NaSS) can be used in a wide range of formation temperature (as high as 150 °C) and salt concentrations (NaCl, CaCl2, as high as 15 wt %). In addition to suitable particle size and mechanically robustness, it was also attributed to the soft, swelling, deformable, toughness and self-healable features of P(MPTC-co-NaSS) gel particles as well as the strong adhesion to negatively charged formations in water, even under high thermal and saline condition. These characteristics also contributed to a long-term plugging performance, beneficial to avoid repeated lost circulation in drilling operation. Besides, this self-healing polyampholyte gel particles dispersed well in saline fluid and maintained stable rheological properties after hot rolling, which was favorable to drilling fluid circulation. This study shown the application potential of self-healing materials as plugging material candidate in petroleum drilling industry.

Strong Tough Polyampholyte Hydrogels via the Synergistic Effect of Ionic and Metal–Ligand Bonds

AbstractDespite existing in biological systems, developing synthetic polyampholyte (PA) hydrogels constructed by both ionic and metal–ligand bonds remains challenging. Herein, a simple secondary equilibrium approach is proposed to fabricate strong and tough PA hydrogels via the synergy of ionic and metal–ligand bonds. The original PA gels (constructed by ionic bonds) are first dialyzed in multivalent metal‐ion solutions to reach a swelling equilibrium and then moved to deionized water to dialyze excess free ions to achieve a new equilibrium. Through this approach, the original PA gel network can be optimized and eventually constructed by ionic and metal–ligand bonds, enabling a synergistic reinforcement. By selecting different original PA gel systems and diverse multivalent metal‐ions, the proposed approach is proved to be generalizable to fabricate strong and tough PA gels. Additionally, the hydrogels have stable ion‐conductivity even at the water‐equilibrium state, making them promising as strain sensors. The viscoelastic and elastic contributions to the mechanical properties of the hydrogels by a viscoelastic model are also discussed to further understand the strengthening and toughening mechanisms. The proposed strategy is simple but effective for achieving strong and tough PA‐based hydrogels. This study also provides new insights for PA hydrogels in electrolyte environments.

Recent Strategies for Strengthening and Stiffening Tough Hydrogels

Hydrogels are major components of the human body. To replace a damaged hydrogel in the body or support/monitor its normal operation, artificial hydrogels similar to those found in nature are required. As the development of morphologically adaptable soft yet tough hydrogels such as double‐network (DN) and polyampholyte (PA) gels, they are applied to soft tissues such as the neural and epithelial tissues with elastic moduli ranging from a few pascals to several kilopascals. However, creating strong and stiff hydrogels emulating stiff load‐bearing connective tissues with elastic moduli in the MPa‐to‐GPa range remains challenging. Herein, recent strategies and potential methods for strengthening and stiffening tough DN and PA gels (such as the reinforcement addition, polymer chain alignment, and solvent exchange) as well as the reinforcing and fracture mechanisms of the resulting hydrogels are summarized. The objective is to provide some insights into the optimal strategy and method for fabricating hydrogels with a combination of strength, stiffness, and toughness, which can emulate natural load‐bearing tissues.

Novel Resins for Efficient Desalination

This paper reports the synthesis and properties of new polymer resins containing strong acid and base groups for optimising applications in desalination. Several polyampholytic gels were synthesised with a ratio of 1:1 of strong acid (sulphonate) and strong base (quaternary ammonium) groups and a zwitterionic resin with a 1:1 strong acid and base ratio. The physico-chemical properties of these highly charged resins were studied in electrolyte solutions over a range of pH values, in particular: effects of chemical cross-linking, water and electrolyte swelling; bulk electrical conductivities and surface charging properties in different pH values. The results from absorption of NaCl showed that the resins have considerable potential for more effective desalination than other resin-based techniques.

Constitutive modeling of bond breaking and healing kinetics of physical Polyampholyte (PA) gel

A three-dimensional finite strain nonlinear viscoelastic model is developed to study the mechanical behavior of a physically cross-linked Polyampholyte (PA) gel. The time dependent behavior of this gel is due to the ionic interactions of oppositely charged monomers randomly distributed along the chain backbone. In this work, we divide the physical cross-links broadly into weak and strong bonds, depending on their survival and reformation characteristics. Our constitutive model connects the strain dependent bond breaking and reforming kinetics in the microscopic regime to the deformation of the gel at the continuum level. We compare the predictions of our model with uniaxial tension, tensile-relaxation, cyclic, and small strain torsional relaxation tests. The material parameters in our model are obtained using least squares optimization. Our theory agrees well with the experimental behavior of the gel.

Constitutive modeling of strain-dependent bond breaking and healing kinetics of chemical polyampholyte (PA) gel.

A finite strain nonlinear viscoelastic constitutive model is used to study the uniaxial tension behaviour of chemical polyampholyte (PA) gel. This PA gel is cross-linked by chemical and physical bonds. Our constitutive model attempts to capture the time and strain dependent breaking and healing kinetics of physical bonds. We compare model prediction by uniaxial tension, cyclic and relaxation tests. Material parameters in our model are obtained by least squares optimization. These parameters gave fits that are in good agreement with the experiments.

Understanding complex dynamics of interfacial reconstruction in polyampholyte hydrogels undergoing mechano-chemo-electrotaxis coupling

Polyampholyte (PA) hydrogels have attracted significant attention for their superior mechanical strength and toughness compared with other conventional hydrogels. In this study, we present a novel thermodynamic approach to understanding the mechano-chemo-electrotaxis coupling and interfacial dynamics in PA hydrogels. Flory–Huggins theory, carried out through an interfacial free-energy model, is the foundation for the quantitative study of the mechanically constitutive relationship of the PA gels. The proposed free-energy model is further extended to describe the mechano-chemo-electrotaxis switching and interfacial dynamics by co-relating the Williams–Landel–Ferry equation and scaling laws. It was concluded that the interfacial bonding strength is the key factor influencing the mechanical strength and reconstruction reversibility of the PA macromolecular gel system. The resulting analytical outcomes showed good agreement with the reported experimental data. We opine that the proposed model will guide the future application of PA hydrogels.

Self-Healable Porous Polyampholyte Hydrogels with Higher Water Content as Cell Culture Scaffolds for Tissue Engineering Applications.

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.

Advances in Synthetic Polyampholytes for Biotechnology and Medicine

Polyampholytes are unique macromolecules containing acid/base or anionic/cationic groups in the main or side chains that mimic the behavior of proteins, polypeptides or polynucleotides. Water-soluble and water-swelling polyampholytes exhibit salt-tolerant, thermal-resistant, shear-stable, self-healing, anti-fouling, self-assembling, and stimuli-responsive properties that provide broad impact as structural biomaterials, drug delivery and chemo-mechanical systems, biosensors, energy storage devices, supercapacitors, actuators etc. In this review we mainly pay attention to fundamental and applied aspects of synthetic polyampholytes in the context of biotechnology and medicine. Among the outlined topics the role of linear and crosslinked amphoteric macromolecules as well as macromolecular complexes of polyampholytes with polyelectrolytes, DNA, proteins and drugs is highlighted. Cryoprotective behavior of synthetic polyampholytes is shown with respect to cell preservation and viability. Injectable, soft, flexible, stretchable, self-healing and stimuli-responsive physically or chemically crosslinked polyampholyte gels that are promising materials for fabrication of artificial tissue, wound dressing, cartilage, cardiovascular, bone defect repair, regenerative medicine and tissue engineering scaffolds, soft actuators and sensors, soft robotics are also in the eyeshot of this review. Hierarchically structured multi-responsive polyampholytic gels, multilayered films and membranes possessing encapsulation–release and “on–off” behaviors are considered as antibiofouling, anticoagulation, and drug delivery system.

Deep insight into ionic transport in polyampholyte gel electrolytes towards high performance solid supercapacitors

A novel polyampholyte gel electrolyte with high ionic conductivity and high mechanical strength was developed and was suitable for supercapacitors.