High-toughness polyacrylamide gel containing hydrophobic crosslinking and its double network gel

Synthesis and Performance Study of Self-Degradable Gel Plugging Agents Suitable for Medium- and Low-Temperature Reservoirs

Aiming at the problems of current similar hydrogel plugging agents, such as poor breaking performance, nonspontaneous degradation, and reservoir pollution which have been plaguing their application in temporary plugging operations, this study has synthesized a cross-linking agent for hydrogels with dimethylaminoethyl acrylate and dibromo-p-xylene as raw materials. With Fourier transform infrared, 1H nuclear magnetic resonance, and thermogravimetric analyses as representations of the structure and thermal stability of the cross-linking agent, a set of self-degrading hydrogel systems has been developed with the cross-linking agent as the core so as to make evaluations on the temperature resistance, plugging performance, and core damage performance of the hydrogel and conduct a study on its gelation kinetics. The research results show that the cross-linking agent shows good thermal stability. When applied in the hydrogel system, the hydrogel has shown high temperature resistance, maintaining gel strength for 5-10 days at 50-90 °C, with viscosity after complete degradation lower than 10 mPa·s. The excellent bearing strength of the hydrogel system has led to a core damage rate below 5%. The study on gelation kinetics of the hydrogel system shows that, with the increase in the concentration of the cross-linking agent, the gelation time of the hydrogel system is shortened, with the reaction order between the cross-linker concentration and the gelation time at about 0.6 under the condition of 50-90 °C.

Preparation and Properties of Composite Double-Network Gel for Inhibiting Coal Spontaneous Combustion

In order to improve the inhibition effect of gel on coal spontaneous combustion, a chitosan (CS)/polyacrylamide (PAM)/metal ion (Al3+) composite double-network gel was developed in this study. The optimum formula of the composite double-network gel was determined using orthogonal experimentation. The microstructure, water retention, compressibility, and anti-destruction properties of the composite double-network gel were analyzed. The inhibition effect of the composite double-network gel on coal spontaneous combustion was studied via infrared spectroscopy and a synchronous thermal analyzer from the micro and macro perspectives. The results show that the composite double-network gel has a denser interpenetrating double-network structure and a larger void ratio than the ordinary gel. The water retention rate was 55% after standing at 150 °C for 12 h. The deformation memory ratio of the composite double-network gel was 78%, which was 26.8% higher than that of the ordinary gel, and the compressive strength also increased by 59.96%. In addition, the critical temperature point and the maximum thermal weight-loss rate temperature point decreased by 7.01 °C and 39.62 °C, respectively, and the composite double-network gel effectively reduced active functional groups in the treated coal sample, such as hydroxyl and aliphatic hydrocarbons. In this study, a CS/PAM/Al3+ composite double-network gel was produced, which exhibited good gel performance and inhibition effects, with physical effects such as the covering, wetting, and cementation of coal.

Innovative Acrylic Resin-Hydrogel Double-Layer Coating: Achieving Dual-Anchoring, Enhanced Adhesion, and Superior Anti-Biofouling Properties for Marine Applications

Traditional anti-corrosion and anti-fouling coatings struggle against the harsh marine environment. Our study tackled this by introducing a novel dual-layer hydrogel (A-H DL) coating system. This system combined a Cu2O-SiO2-acrylic resin primer for anchoring and controlled copper ion release with a dissipative double-network double-anchored hydrogel (DNDAH) boasting superior mechanical strength and anti-biofouling performance. An acrylamide monomer was copolymerized and cross-linked with a coupling agent to form the first irreversible network and first anchoring, providing the DNDAH coating with mechanical strength and structural stability. Alginate gel microspheres (AGMs) grafted with the same coupling agent formed the second reversible network and second anchoring, while coordinating with Cu2+ released from the primer to form a system buffering Cu2+ release, enabling long-term antibacterial protection and self-healing capabilities. FTIR, SEM, TEM, and elemental analyses confirmed the composition, morphology, and copper distribution within the A-H DL coating. A marine simulation experiment demonstrated exceptional stability and anti-fouling efficacy. This unique combination of features makes A-H DL a promising solution for diverse marine applications, from ship hulls to aquaculture equipment.

The physical and structural properties of acid-Ca2+ induced casein-alginate/Ca2+ double network gels

The design of protein or polysaccharide interpenetrating network gels according to their physicochemical properties is required to obtain the desired properties of hydrogels. In this study, a method was proposed to prepare casein-calcium alginate (CN-Alg/Ca²⁺) interpenetrating double-network gels by the release of calcium from a calcium retarder during acidification to form calcium-alginate (Alg/Ca²⁺) gel and casein (CN) acid gel. Compared with the casein-sodium alginate (CN-Alg) composite gel, the CN-Alg/Ca²⁺ dual gel network with an interpenetrating network gel structure has better water-holding capacity (WHC) and hardness. The rheology and microstructure results showed that the dual-network gels of CN and Alg/Ca²⁺ induced by gluconic acid-δ-sodium (GDL) and calcium ions were the network structure of the Alg/Ca²⁺ gel, which was the "first network", and the CN gel, which was the "second network". It was proven that the microstructure, texture characteristics, and WHC of the double-network gels could be regulated by changing the concentration of Alg in the double-network gels and that the 0.3 % CN-Alg/Ca²⁺ double gels showed the highest WHC and firmness values. The aim of this study was to provide useful information for the preparation of polysaccharide-protein mixed gels in the food industry or other fields.

Research Progress of Intelligent Polymer Plugging Materials

Intelligent polymers have become the focus of attention worldwide. Intelligent polymer materials through organic synthesis methods are used to make inanimate organic materials become “feeling” and “sentient”. Intelligent polymer materials have been applied in actual engineering production, and they are becoming a new research topic for scientists in various fields and countries, especially in the areas of drilling and plugging. The development of intelligent polymer materials can provide new solutions and technical means for drilling and plugging. Unlike traditional plugging materials, intelligent polymer plugging materials can cope with environmental changes. They have the characteristics of a strong target, good plugging effect, and no damage to the reservoir. However, there are currently no reviews on intelligent polymer plugging materials in the drilling field, so this paper fills that gap by reviewing the research progress of intelligent polymer plugging materials. In addition, this paper describes the mechanism and application status of intelligent polymer shape-memory polymers, intelligent polymer gels, intelligent polymer membranes, and intelligent polymer bionic materials in drilling and plugging. It is also pointed out that some intelligent polymer plugging materials still have problems, such as insufficient toughness and a poor resistance to salt and high temperature. At the same time, some suggestions for future research directions are also presented for reference.

Temperature- and strain-dependent transient microstructure and rheological responses of endblock-associated triblock gels of different block lengths in a midblock selective solvent

Endblock associative ABA gels in midblock selective solvents are attractive due to their easily tunable mechanical properties. Here, we present the effects of A- and B-block lengths on the rheological properties and microstructure of ABA gels by considering three low and one high polymer concentrations. The triblock polymer considered is poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) [PMMA-PnBA-PMMA] and the midblock solvent is 2-ethyl-1-hexanol. The gelation temperature has been found to be strongly dependent on the B-block (PnBA) length, as longer B-blocks facilitate network formation resulting in higher gelation temperature even with lower polymer chain density. Longer A-blocks (PMMA chains) make the endblock association stronger and significantly increase the relaxation time of gels. Temperature-dependent microstructure evolution for the gels with high polymer concentration reveals that the gel microstructure does not change significantly after the gel formation takes place. The dynamic change of microstructure in an applied strain cycle was captured using RheoSAXS experiments. The microstructure orients with the applied strain and the process is reversible in nature, indicating no significant A-block pullout. Our results provide new understandings regarding the temperature and strain-dependent microstructural change of ABA gels in midblock selective solvents.

Fabrication of Microcapsules by the Combination of Biomass Porous Carbon and Polydopamine for Dual Self-Healing Hydrogels

Artificial development of smart materials from agricultural waste or food residues is particularly desirable for green chemistry. In this paper, dual-network self-healing hydrogels were successfully fabricated by using functional microcapsules. These microcapsules were established by biomass porous carbon (PC) after recycling of apple residues. Glutaraldehyde (GA) as the healing agent was embedded in the porous carbon, and the outer surface was coated with polydopamine (PDA). After the microcapsules were added, modifying guar gum-type hydrogels were successfully obtained with dual self-healing performance by the combination of a healing agent and metal-ligand coordination. The self-healing efficiency was about 89.9% from the tension test, and the fracture strength was measured as 7.68 MPa. These results not only highlight a new idea for the utilization of apple residues but also provide a new method for the preparation of excellent self-healing hydrogels.

Rigid and Strong Thermoresponsive Shape Memory Hydrogels Transformed from Poly(vinylpyrrolidone- co-acryloxy acetophenone) Organogels

Shape memory hydrogels (SMHs) have a wide range of potential practical applications. However, the mechanically weak and soft nature of most SMHs strongly impedes their applications. Here, we report a novel kind of thermal-responsive SMH with high tensile strength and high elastic moduli. Organogels are first prepared by the copolymerization of a hydrophilic monomer N-vinylpyrrolidone (NVP) and a hydrophobic monomer acryloxy acetophenone (AAP) in N, N'-dimethylformamide (DMF) solutions, and then, poly(vinylpyrrolidone- co-acryloxy acetophenone) [poly(NVP- co-AAP)] hydrogels are obtained by solvent exchange with water. Because of the strong and reversible hydrophobic association and π-π stacking of acetophenone groups, the poly(NVP- co-AAP) hydrogels exhibit tensile strengths up to 8.41 ± 0.83 MPa and Young's moduli up to 94.2 ± 1.3 MPa, which are more than 1 or 3 orders of magnitude higher than those of the organogels, respectively. The poly(NVP- co-AAP) hydrogels exhibit good shape memory behaviors, with a complete fixation ratio and a recovery ratio of 74-89%, as well as very fast shape-fixing and recovering rates (in seconds). These rigid and strong hydrogels are demonstrated to be an ideal shape memory material for surgical fixation devices to wrap around and support various shapes of limbs.

One-Pot Synthesis of a Double-Network Hydrogel Electrolyte with Extraordinarily Excellent Mechanical Properties for a Highly Compressible and Bendable Flexible Supercapacitor

High-performance hydrogel electrolytes play a crucial role in flexible supercapacitors (SCs). However, the unsatisfactory mechanical properties of widely used polyvinyl alcohol-based electrolytes greatly limit their use in the flexible SCs. Here, a novel Li₂SO₄-containing agarose/polyacrylamide double-network (Li-AG/PAM DN) hydrogel electrolyte was synthesized by a heating-cooling and subsequent radiation-induced polymerization and cross-linking process. The Li-AG/PAM DN hydrogel electrolyte possesses extremely excellent mechanical properties with a compression strength of 150 MPa, a fracture compression strain of above 99.9%, a tensile strength of 1103 kPa, and an elongation at break of 2780%, greatly superior to those have been reported. It also achieves a high ionic conductivity of 41 mS cm^-1 originating from its interconnected three-dimensional porous network structure that provides a three-dimensional channel for ionic migration. Compared to the SC applying Li₂SO₄ aqueous solution electrolyte, the corresponding flexible Li-AG/PAM DN hydrogel electrolyte-SC presents lower charge-transfer resistance, better ionic diffusion, being closer to ideal capacitive behaviors, superior rate capability, and better cycling stability, owing to the improved ionic transport in the Li-AG/PAM DN hydrogel electrolyte and electrode interfaces. Moreover, after testing with overcharge, short circuit, and high temperature, the capacitance of the Li-AG/PAM DN hydrogel electrolyte-SC can still be well maintained. Furthermore, the electrochemical properties of the Li-AG/PAM DN hydrogel electrolyte-SC remain almost intact under different compression strains/bending angles and even after 1000 compression/bending cycles. It is expected that the Li-AG/PAM DN hydrogel electrolyte may have broad applications in modern flexible and wearable electronics.

A Micellar-Hydrogel Nanogrid from a UV Crosslinked Inulin Derivative for the Simultaneous Delivery of Hydrophobic and Hydrophilic Drugs

Hydrogels are among the most common materials used in drug delivery, as polymeric micelles are too. They, preferentially, load hydrophilic and hydrophobic drugs, respectively. In this paper, we thought to combine the favorable behaviors of both hydrogels and polymeric micelles with the specific aim of delivering hydrophilic and hydrophobic drugs for dual delivery in combination therapy, in particular for colon drug delivery. Thus, we developed a hydrogel by UV crosslinking of a methacrylated (MA) amphiphilic derivative from inulin (INU) (as known INU is specifically degraded into the colon) and vitamin E (VITE), called INVITEMA. The methacrylated micelles were physicochemically characterized and subjected to UV irradiation to form what we called the "nanogrids". The INVITEMA nanogrids were characterized by DSC, SEM, TEM, water uptake and beclomethasone dipropionate (BDP) release. In particular, the release of the hydrophobic drug was specifically assessed to verify that it can spread along the hydrophilic portions and, therefore, effectively released. These systems can open new pharmaceutical applications for known hydrogels or micelle systems, considering that in literature only few examples are present.

A review on acrylic based hydrogels and their applications in wastewater treatment

The acrylic based hydrogels have attracted the attention of many researchers in the field of pollutants adsorption such as dyes and metal cations due to their high swelling and adsorption capacities. This review introduces acrylic based hydrogels and focuses on their adsorption properties. We first described the methods for synthesizing hydrogels. Usual methods of characterization of acrylic based hydrogels such as swelling, adsorption capacity and desorption efficiency of the pollutants have been investigated. In addition, the adsorption isotherm and kinetic models which determine the mechanism of pollutants' adsorption by hydrogels have been introduced and relations that determine the values of thermodynamic parameters which define accomplishment of adsorption process have been investigated. In the following sections, a perfect insight has been provided on natural and synthetic acrylic based hydrogels. The effective parameters of swelling and adsorption by acrylic based hydrogels have been reviewed and the mechanism of pollutant's adsorption by acrylic based hydrogels has been discussed.

Polymeric ionic liquid gels composed of hydrophilic and hydrophobic units for high adsorption selectivity of perrhenate

The removal of TcO₄⁻ from aqueous solutions has attracted more and more attention recently, and ReO₄⁻ has been widely used as its natural analog. In this work, polymeric ionic liquid gel adsorbents, PC₂-C₁₂vimBr, with high adsorption capacity and selectivity towards ReO₄⁻ were synthesized by radiation-induced polymerization and crosslinking. PC₂-C₁₂vimBr was composed of two monomers: a hydrophobic unit, 1-vinyl-3-dodecylimidazolium bromide for high selectivity, and a hydrophilic unit, 1-vinyl-3-ethylimidazolium bromide for improved kinetics. A gel fraction up to 90% could be achieved under 40 kGy with varied monomer ratios. The adsorption of PC₂-C₁₂vimBr gels for ReO₄⁻ was evaluated by batch adsorption. The PC₂-C₁₂vimBr gel containing 20 mol% hydrophilic unit (named PC₂-C₁₂vimBr-A) could significantly improve the adsorption kinetics, which had an equilibrium time of ca. 24 h. The adsorption capacity obtained from the Langmuir model was 559 mg g⁻¹ (Re/gel). The selective factor against NO₃⁻ was 33.4 ± 1.9, which was more than 10 times higher than that of PC₂vimBr, and it could maintain ReO₄⁻ uptake as high as 100 mg g⁻¹ in 0.5 mol kg⁻¹ HNO₃. The ΔH^Θ and ΔS^Θ of the NO₃⁻/ReO₄⁻ ion-exchange reaction of PC₂-C₁₂vimNO₃-A were −16.9 kJ mol⁻¹ and 29 J mol⁻¹ K⁻¹, respectively, indicating physical adsorption. The adsorption mechanism of ReO₄⁻ onto PC₂-C₁₂vimBr-A gel was ion-exchange, and it could be recovered using 5.4 mol kg⁻¹ HNO₃.

Polymeric ionic liquid gels composed of hydrophilic and hydrophobic units with high adsorption selectivity towards perrhenate were synthesized.

Manufacturing of hydrogel biomaterials with controlled mechanical properties for tissue engineering applications

Hydrogels have been recognized as crucial biomaterials in the field of tissue engineering, regenerative medicine, and drug delivery applications due to their specific characteristics. These biomaterials benefit from retaining a large amount of water, effective mass transfer, similarity to natural tissues and the ability to form different shapes. However, having relatively poor mechanical properties is a limiting factor associated with hydrogel biomaterials. Controlling the biomechanical properties of hydrogels is of paramount importance. In this work, firstly, mechanical characteristics of hydrogels and methods employed for characterizing these properties are explored. Subsequently, the most common approaches used for tuning mechanical properties of hydrogels including but are not limited to, interpenetrating polymer networks, nanocomposites, self-assembly techniques, and co-polymerization are discussed. The performance of different techniques used for tuning biomechanical properties of hydrogels is further compared. Such techniques involve lithography techniques for replication of tissues with complex mechanical profiles; microfluidic techniques applicable for generating gradients of mechanical properties in hydrogel biomaterials for engineering complex human tissues like intervertebral discs, osteochondral tissues, blood vessels and skin layers; and electrospinning techniques for synthesis of hybrid hydrogels and highly ordered fibers with tunable mechanical and biological properties. We finally discuss future perspectives and challenges for controlling biomimetic hydrogel materials possessing proper biomechanical properties.

STATEMENT OF SIGNIFICANCE

Hydrogels biomaterials are essential constituting components of engineered tissues with the applications in regenerative medicine and drug delivery. The mechanical properties of hydrogels play crucial roles in regulating the interactions between cells and extracellular matrix and directing the cells phenotype and genotype. Despite significant advances in developing methods and techniques with the ability of tuning the biomechanical properties of hydrogels, there are still challenges regarding the synthesis of hydrogels with complex mechanical profiles as well as limitations in vascularization and patterning of complex structures of natural tissues which barricade the production of sophisticated organs. Therefore, in addition to a review on advanced methods and techniques for measuring a variety of different biomechanical characteristics of hydrogels, the new techniques for enhancing the biomechanics of hydrogels are presented. It is expected that this review will profit future works for regulating the biomechanical properties of hydrogel biomaterials to satisfy the demands of a variety of different human tissues.

High performances of dual network PVA hydrogel modified by PVP using borax as the structure-forming accelerator

A dual network hydrogel made up of polyvinylalcohol (PVA) crosslinked by borax and polyvinylpyrrolidone (PVP) was prepared by means of freezing-thawing circles. Here PVP was incorporated by linking with PVA to form a network structure, while the introduction of borax played the role of crosslinking PVA chains to accelerate the formation of a dual network structure in PVA/PVP composite hydrogel, thus endowing the hydrogel with high mechanical properties. The effects of both PVP and borax on the hydrogels were evaluated by comparing the two systems of PVA/PVP/borax and PVA/borax hydrogels. In the former system, adding 4.0% PVP not only increased the water content and the storage modulus but also enhanced the mechanical strength of the final hydrogel. But an overdose of PVP just as more than 4.0% tended to undermine the structure of hydrogels, and thus deteriorated hydrogels’ properties because of the weakened secondary interaction between PVP and PVA. Likewise, increasing borax could promote the gel crosslinking degree, thus making gels show a decrease in water content and swelling ratio, meanwhile shrinking the pores inside the hydrogels and finally enhancing the mechanical strength of hydrogels prominently. The developed hydrogel with high performances holds great potential for applications in biomedical and industrial fields.

Self-healable, tough and highly stretchable hydrophobic association/ionic dual physically cross-linked hydrogels

In this work, we describe a novel method for the production of tough and highly stretchable hydrogels with self-healing behavior, tensile strength of 150–300 kPa and stretch at break of 2400–2800%.

High-Strength, Tough, Fatigue Resistant, and Self-Healing Hydrogel Based on Dual Physically Cross-Linked Network

Hydrogels usually suffer from low mechanical strength, which largely limit their application in many fields. In this Research Article, we prepared a dual physically cross-linked hydrogel composed of poly(acrylamide-co-acrylic acid) (PAM-co-PAA) and poly(vinyl alcohol) (PVA) by simple two-steps methods of copolymerization and freezing/thawing. The hydrogen bond-associated entanglement of copolymer chains formed as cross-linking points to construct the first network. After being subjected to the freezing/thawing treatment, PVA crystalline domains were formed to serve as knots of the second network. The hydrogels were demonstrated to integrate strength and toughness (1230 ± 90 kPa and 1250 ± 50 kJ/m(3)) by the introduction of second physically cross-linked network. What̀s more, the hydrogels exhibited rapid recovery, excellent fatigue resistance, and self-healing property. The dynamic property of the dual physically cross-linked network contributes to the excellent energy dissipation and self-healing property. Therefore, this work provides a new route to understand the toughness mechanism of dual physically cross-linked hydrogels, hopefully promoting current hydrogel research and expanding their applications.

A new imidazolium-based polymeric ionic liquid gel with high adsorption capacity for perrhenate

New imidazolium-based polymeric ionic liquid gel with high adsorption capacity for perrhenate prepared by γ-radiation induced polymerization and crosslinking.