Reversible Gel Research Articles

On the rheological properties of silica – Polyethylene oxide dispersions: Shake gels I the effect of polymer concentration and temperature

Shake-gels are aqueous mixtures of silica and Poly(ethylene-oxide) (PEO) that form reversible gels when subjected to an applied force, such as shaking. This shear-thickening effect can be observed using a rheometer, which shows discrete, sudden changes in the material's viscosity. Preliminary qualitative investigations have shown that the gelation time varies depending on the conditions used. We also measure the time required for the gel to relax and revert to its liquid state. To quantify the relationships between these variables and better understand the process and kinetics, a systematic investigation was conducted, focusing on the effects of polymer concentration and temperature on gelation and relaxation times. Experiments were carried out using a rheometer with double-gap concentric cylinder geometry, applying a constant shear rate to samples with varying polymer concentrations and temperatures. The results showed that, at a fixed shear rate, gelation and relaxation times varied significantly, ranging from a few seconds to over an hour. Both gelation and relaxation occurred more rapidly as polymer concentration increased. Additionally, higher temperatures led to faster gelation and relaxation times and vice versa.

Volumetric 3D Printing of Endoskeletal Soft Robots.

Computed Axial Lithography (CAL) is an emerging technology for manufacturing complex parts, all at once, by circumventing the traditional layered approach using tomography. Overprinting, a unique additive manufacturing capability of CAL, allows for a 3D geometry to be formed around a prepositioned insert where the occlusion of light is compensated for by the other angular projections. This method opens the door for novel applications within additive manufacturing for multi-material systems such as endoskeletal robots. Herein, this work presents one such application with a simple Gelatin Methacrylate (GelMA)hydrogel osmotic actuator with an embedded endoskeletal system. GelMA is an ideal material for this application as it is swellable and has reversible thermal gelation, enabling suspension of the endoskeleton during printing. By tuning the material formulation, the actuator design, and post-processing, swelling-induced bending actuation of 60 degrees is achieved. To aid in the printing process, a simple computational method for determining the absolute dose absorbed by the resin allowing for print time prediction is also proposed.

Development of novel protein-rich foods: Studies of composite hydrogels formed from potato proteins and gellan gums with different degrees of acylation

The textural attributes of mixed hydrogels formed from potato protein (PP) and gellan gum (GG) were examined for their potential application as novel protein-rich foods (NPFs). Initially, the properties of gels formed by the individual biopolymers were characterized using dynamic shear rheology, compression testing, and confocal fluorescence microscopy. Rheological analysis revealed that PP dispersions formed irreversible heat-set gels, whereas GG formed reversible cold-set gels at lower temperatures. The effects of adding PP to high acyl gellan gum (HA-GG) or low acyl gellan gum (LA-GG) solutions on the microstructure and rheology of the mixed gels formed were then examined. The PP/LA-GG composite gels had a highly heterogeneous microstructure consisting of protein-rich and polysaccharide-rich regions. In contrast, the PP/HA-GG composite gels had a more uniform microstructure. Interestingly, the incorporation of the PP weakened the PP/LA-GG composite gels (antagonism) but strengthened the PP/HA-GG composite gels (synergism), which was mainly attributed to their different impacts on gel microstructure. This study shows that semi-solid plant protein-dietary fiber composites can be formed with a variety of textural attributes by altering the nature and concentration of biopolymers used to formulate them. These mixed gels may be useful for the creation of NPFs. This study also highlights the complexity of the interactions between different food biopolymers and their impacts on food properties, highlighting the need for further research on understanding structure-function relationships in multicomponent biopolymer materials.

Thermally reversible emulsion gels and high internal phase emulsions based solely on pea protein for 3D printing

This work compared thermally reversible emulsion gels and high internal phase emulsions (HIPEs) based on pea protein for 3D printing at different oil volume fraction (ϕ) ranging from 0.2 to 0.8. Thermally reversible emulsion gels were obtained with ϕ from 0.2 to 0.65, which melt into liquid emulsion as temperature increased, and recovered into emulsion gels upon cooling as reflected by consistent rheological measurements. The Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the transition between intermolecular β-sheet at 1630 cm−1 and intramolecular β-sheet at 1618 cm−1 through reversible H-bonds upon changes in temperature, which was responsible for the repeated thermo-reversibility. With ϕ increased to 0.74–0.8, HIPEs were confirmed by Scanning Electron Microscope (SEM) and Confocal Laser Scanning Microscope (CLSM), yet the thermo-reversibility was not maintained. In addition, the thermally reversible emulsion gels exhibited strong shear-thinning and thixotropic recovery through the untangling and reformation of the H-bonded gel network. Whereas deformation and restructuring of the close packed droplets were responsible for such behaviors in HIPEs. 3D printing test has further demonstrated excellent performance of thermally reversible emulsion-filled gel with ϕ 0.4, comparable to HIPE with ϕ 0.74 b y enabling printed objects with high shape fidelity (printability index (Pr) of 0.95–1.08) and shape stability (prints height maintenance (Hm) of 82.2%–87.8%). This research opens up thermally reversible emulsion gels solely from sustainable protein source for 3D printing, with low oil content and no synthetic ingredients needed.

Investigation of the rheological behaviour for improved extrusion-based additive manufacturing of polymer composites based on dissociative dynamic covalent bonds

More complex 3D structures were manufactured out of reversible covalent polymer networks using multi-material extrusion-based additive manufacturing. The rheological behaviour of reversible polymer networks based on the thermoreversible Diels-Alder reaction was optimized through the addition of different types of nanoclays and carbon black. The extrudability and deposition of the composites improved up to 5 wt% nanoclay, as the viscosity behaviour increased by an order of magnitude in the nozzle and by two orders of magnitude at the print bed temperature, without affecting the reversible gel transition temperature and the healing performance. An electrically conductive composite with 20 wt% carbon black and 1 wt% nanoclay could be printed using nozzle sizes down to 0.3 mm, resulting in higher resolution and accuracy than the pristine polymer networks. The percolating filler network enabled the printing of overhangs and hollow structures without the need for support material with perfect mechanical and electrical isotropy. Multi-material printing combining the electrically conductive and non-conductive composites enabled manufacturing self-healing deformation and force sensors that could recover their sensing performance upon damage healing at 90 °C for one hour.

Strong and Thermo-Switchable Gel Adhesion Based on UCST-Type Phase Transition in Deep Eutectic Solvent.

It remains a great challenge to achieve strong and reversible hydrogel adhesion. Hydrogel adhesives also suffer from poor environmental stability due to dehydration. To overcome these problems, here reversible adhesive gels are designed using a new switching mechanism and new solvent. For the first time, the study observes UCST (upper critical solution temperature)-type thermosensitive behaviors of poly(benzyl acrylate) (PBnA) polymer and gel in menthol:thymol deep eutectic solvents (DESs). The temperature-induced phase transition allows adjusting cohesive force, and hence adhesion strength of PBnA gels by temperature. To further improve the mechanical and adhesion properties, a peptide crosslinker is used to allow energy dissipation when deforming. The resulting eutectogel exhibits thermal reversible adhesion with a high switching ratio of 14.0. The adhesion strength at attachment state reaches 0.627MPa, which is much higher than most reversible adhesive hydrogels reported before. The low vapor pressure of DES endows the gel excellent environmental stability. More importantly, the gel can be repeatedly switched between attachment and detachment states. The strong and reversible gel adhesive is successfully used to design soft gripper for the transport of heavy cargos and climbing robot capable of moving on vertical and inverted surface in a manner similar to gecko.

Advancing bacterial endophyte encapsulation in alginate for sustainable agriculture: Method comparisons, morphology and viability assessment

This study focused on encapsulating Kosakonia radicincitans in alginate beads and capsules using the Ionic External Gelation (IEG) and Reverse Gelation (RG) methods. The results showed that both IEG and RG methods provided high encapsulation efficiencies (84.61% and 85.22%, respectively) without additives. The beads and capsules displayed distinct morphological characteristics, with beads exhibiting smooth and homogeneous surfaces, while capsules appeared rougher and more irregular. The biodegradability study revealed that the encapsulated materials exhibited higher mass loss at elevated temperatures, indicating the potential rapid release of bacterial cells into the soil-plant system. However, the viability of bacteria persisted around the particles even after 60 days in the soil, suggesting that drying temperature and ambient temperature play crucial roles in determining the biofertilizer's persistence in the soil. This research highlights the complexities associated with the long-term effects of encapsulated biofertilizers, which are critical for advancing toward sustainable environmental and agricultural solutions.

Dynamically Reversible Gelation of Electrolyte for Efficient Wide‐Temperature Adaptable Energy Storage

AbstractQuasi‐solid‐state electrolytes (QSEs) via gelation of liquid electrolytes (LEs) are perspective protocols for constructing ingenious potassium‐ion batteries (PIBs) due to the combined advantages of both liquid and solid state. However, most of QSEs yet researched face a trade‐off among low temperature adaptability and safely high temperature operation. Herein, in situ reversible gelation of Ni‐crosslinked pentaerythritol tetrakis (3‐mercaptopropionate) (PETMP‐Ni) co‐polymerized with tyramine‐modified hyaluronic acid (HA‐Tyr) (PHA) modified B, N modified carbon spheres (BNC) enclosing by red P (RP) is backed with compatible electrode‐electrolyte interface with laponite filler (L). Such high reversible in situ gelation displays high low temperature adaptability by LEs, and extraordinary safety in high temperature steered by QSEs, benefiting from topologic space crowding effect (TSCE) and reverse trap of Ni single atoms (Ni SAs). This work enlightens the missing prospects in constructing reversible in situ sol–gel strategy coupled by topologic space crowding effect and reverse SAs trapping stimulate toward revival hybrid electrode for wide‐temperature adaptive batteries.

Water-stable boroxine structure with dynamic covalent bonds

Boroxines are significant structures in the production of covalent organic frameworks, anion receptors, self-healing materials, and others. However, their utilization in aqueous media is a formidable task due to hydrolytic instability. Here we report a water-stable boroxine structure discovered from 2-hydroxyphenylboronic acid. We find that, under ambient environments, 2-hydroxyphenylboronic acid undergoes spontaneous dehydration to form a dimer with dynamic covalent bonds and aggregation-induced enhanced emission activity. Intriguingly, upon exposure to water, the dimer rapidly transforms into a boroxine structure with excellent pH stability and water-compatible dynamic covalent bonds. Building upon these discoveries, we report the strong binding capacity of boroxines toward fluoride ions in aqueous media, and develop a boroxine-based hydrogel with high acid–base stability and reversible gel–sol transition. This discovery of the water-stable boroxine structure breaks the constraint of boroxines not being applicable in aqueous environments, opening a new era of researches in boroxine chemistry.

Enhanced lubrication and photothermal conversion via dynamically reversible supramolecular oil gels filled with MXene@mGLM composites

Preparation of dynamic reversible supramolecular oil gels filled with MXene@mGLM composites, which exhibit good lubrication properties and photothermal conversion properties.

Decoupling Li+ conductivity and mechanical stability in a thermally reversible concentrated sulfone-based gel electrolyte for lithium metal batteries

This work presents a mechanically strong and highly Li+-conductive gel electrolyte featuring thermally induced electrode wetting and healing, which holds great promise in solid-state lithium-metal batteries and other flexible and wearable devices.

Tannic acid-enriched nanocellulose hydrogels improve physical and oxidative stability of high-internal-phase Pickering emulsions

A cellulose suspension and tannic acid (TA) were co-sonicated to prepare TA-incorporated nanocellulose hydrogels with the aim of improving the physical and oxidative stability of high-internal-phase emulsions (HIPEs). Cellulose nanocrystal (CNC) hydrogels were used to stabilize HIPEs, relying on the interfacial adsorption behavior of CNCs and the reversible gelation properties of hydrogels. TA was incorporated due to its ability to improve emulsification performance and antioxidant properties. Introducing TA enhanced the gel strength of hydrogels by decreasing the interfibrillar distance. The utilization of CNC-TA hydrogels effectively improved physical properties of HIPEs. This improvement included a reduction in droplet size from the initial 103.41 μm to 39.66 μm, an enhancement of the gel structure, and an improvement in storage stability. A denser and orderly interfacial structure was formed in CNCs-TA hydrogel stabilized HIPEs due to anchoring TA at the interface driven by the hydrogen-bonding interaction between CNCs and TA. This densely interfacial layer with good antioxidant activity markedly enhanced the oxidative stability of emulsions, as evidenced by the low level of oxidation products in HIPEs. This study has the potential to extend the utilization of CNC-stabilized emulsions to new applications in the food, cosmetic, and pharmaceutical industries.

Halloysite nanotubes as nano-support matrix for programming the photo/H2O dual triggered reversible gel actuator

Gel actuators are a kind of soft intelligent material that can convert external stimuli into deformations to generate mechanical responses. The development of gel actuators with advanced structures to integrate multiple responsiveness, programmability, and fast deformation ability is urgently needed. Here, we explored a poly(7-(2-methacryloyloxyethoxy)-4-methylcoumarin-co-acrylic acid-co-glycol) ternary gel network as an actuator with reprogrammable photo/H2O dual responsibilities. In such a design, [2 + 2] photodimerization and photocleavage reactions of coumarin moieties can be realized under 365 and 254 nm light irradiation, respectively, affording reversible photodriven behaviour of the gels. The abundant carboxylic acid in the backbone has the capacity to form additional crosslinks to assist and accelerate the photodriven behaviour. The incorporation and orientation of halloysite nanotubes (HNTs) in gel matrices support an axial direction force and result in a more controllable and programmable actuating behaviour. The synergistic response enables fast grasping-releasing of 5-times the weight of the object in water within 10 min by fabricating HNT-incorporated gels as a four-arm gripper.

A trade-off between hardness and stretchability of associative networks during the sol-to-gel transition

The trade-off between hardness and stretchability is a cornerstone of materials science. Balancing this trade-off is important in the molecular design of both chemical and physical networks. In this study, we report the quantitative trade-off at the molecular level for physical networks. Namely, we analyze, based on the reversible gelation model, a scaling relationship between the characteristic terminal relaxation modulus Gc in linear viscoelasticity and the stretch ratio λmax at the stress overshoot during the nonlinear elongation flow for unentangled randomly associative polymers, i.e., λmax ∼ Gc−0.17 and λmax ∼ Gc−0.33 in the mean-field and critical-percolation regimes, respectively. We use sulfonated polystyrene having different alkali counterions as a model system to test the relationship. The exponent of λmax ∼ Gc−0.25 seen in the experiment is in between the two theoretical values. We also discuss the quantitative deviation with respect to the size distribution of the network strands.

A smart low-molecular-mass naphthalene-pyrazoline gelator: Gelation behavior and selective fluorescent detection Cu2+

A smart low-molecular-mass organic gelator based on naphthalene-pyrazoline has been designed and synthesized. The gelator G can form a thermo reversible stable gel in tert-butanol, cyclohexane, cyclohexanol, and DMSO through self-assembly, it emits blue and yellow-green fluorescence under ultraviolet radiation. Notably, it has multiple stimulus responses of light, heat, shock and ion. In addition, it could act as an efficient fluorescent probe for the selective sensing of Cu2+ in the solution containing water. The detection limit of Cu2+ in THF deionized aqueous solution (V:V = 9:1) is 5.65 × 10−8 M. The complex ratio of G to Cu2+ is 1:1. In addition, the G has good biocompatibility in living cells.

Colloidal Clusters and Networks Formed by Oppositely Charged Nanoparticles with Varying Stiffnesses.

Colloidal clusters and gels are ubiquitous in science and technology. Particle softness has a strong effect on interparticle interactions; however, our understanding of the role of this factor in the formation of colloidal clusters and gels is only beginning to evolve. Here, we report the results of experimental and simulation studies of the impact of particle softness on the assembly of clusters and networks from mixtures of oppositely charged polymer nanoparticles (NPs). Experiments were performed below or above the polymer glass transition temperature, at which the interaction potential and adhesive forces between the NPs were significantly varied. Hard NPs assembled in fractal clusters that subsequently organized in a kinetically arrested colloidal gel, while soft NPs formed dense precipitating aggregates, due to the NP deformation and the decreased interparticle distance. Importantly, interactions of hard and soft NPs led to the formation of discrete precipitating NP aggregates at a relatively low volume fraction of soft NPs. A phenomenological model was developed for interactions of oppositely charged NPs with varying softnesses. The experimental results were in agreement with molecular dynamics simulations based on the model. This work provides insight on interparticle interactions before, during, and after the formation of hard-hard, hard-soft, and soft-soft contacts and has impact for numerous applications of reversible colloidal gels, including their use as inks for additive manufacturing.

Linear viscoelasticity, nonlinear rheology and applications of polyethylene terephthalate vitrimers

AbstractTo enhance mechanical properties and processing performance of poly(ethylene terephthalate) (PET), it was upcycled to processable PET vitrimers with different crosslinking degrees by introducing dynamic network. The thermodynamics and linear viscoelasticity of PET vitrimers were explored by non‐isothermal crystallization, isothermal sweep, frequency sweep and stress relaxation after incorporation of network. In particular, rheology experiments are sensitive to network structure and bond exchange mechanism in vitrimers. The pseudo‐master curves show that relaxation processes are composed of three characteristic regions: Rouse‐type relaxation of network strands, rubbery plateau and terminal relaxation of network, which is consistent with reversible gelation (RG) model. Two distinct (flow and chemical reaction) activation energies, are obtained by time–temperature superposition principle due to different temperature dependences of two relaxation behaviors. In addition, nonlinear rheology of PET vitrimers was investigated by extensional flow and start‐up shear at the same Weissenberg number, and obvious strain hardening behavior were observed in all vitrimers. However, vitrimers with different crosslinking density exhibited distinct strain hardening trends as increase of extensional rate, corresponding to the ductility of material. On the basis of kinetics study, self‐repairing and welding properties are further quantitatively explored for industrial applications.

Copolymer intercalated hydrotalcite sustained release-type fluid loss additive for water-based drilling fluid: Synthesis, characterization, and performance evaluation

The polyanionic copolymer fluid loss additive (PSADM) intercalated hydrotalcite sustained release-type fluid loss additive (PSADM–LDH) was fabricated through in situ intercalation polymerization to alleviate the deterioration of filtration and rheological properties of water-based drilling fluid (WBDF) under extreme geological conditions (e.g., high-temperature and alt-gypsum formations). The PSADM between layers of LDH can be slowly exchanged by anions in WBDF to give full play to its original efficiency. Results of FT–IR, TG and XRD demonstrate that the PSADM successfully intercalated the layers of LDH, and the intercalation rate was approximately 14 wt%. In addition, results of filtration measurements of WBDF demonstrate that the PSADM–LDH significantly decreased the filtration volume, even though after thermal rolling at 200 °C the filtration volume of brine drilling fluids contained 2 wt% PSADM–LDH was reduced by approximately 50% compared with PSADM. Moreover, the introduction of PSADM–LDH enhanced the thixotropy of WBDF because of forming a dynamic reversible gel structure by copolymer and charged clay colloidal particles (LDH and bentonite), which is conducive to giving full play to the water power of the bit, and carrying and suspending the drill cutting well in the annulus. Therefore, PSADM–LDH has broad application prospects for exploring and developing super-deep reservoirs.

Kinetic Improvement of the Gel-sol Transition of Thermoresponsive Hydrogels Utilizing a High Surface Area Host

Rapid reversible phase transitions of biocompatible thermoresponsive sealants (TRS) upon cooling are required for their practical application in many sectors. The gel–sol transition rate of the TRS studied here [poly(N-isopropylacrylamide-co-butyl acrylate 95:5, number-averaged molecular weight = 7–64 kg mol–1] after being heated to 50 °C is slowed dramatically. The unheated materials return to a free-flowing sol form in a matter of minutes, while the heated materials remain in a gel or solid form for hours. The gel–sol transition of these polymers is enhanced in the presence of a high surface area host in the form of open-cell foams such as polyurethane (PUR), polyimide (PIM), hydrophilic polyurethane Aquazone (AQZ), and neoprene (NEO). An enhanced rate of sol formation on cooling and high TRS recovery (74–99%) were observed across a range of foam types and pore sizes when compared to samples stored without a host (9% recovery). Polyurethane demonstrates the greatest increase in TRS recovery (∼10-fold) after storing the TRS solution at 50 °C followed by cooling for 10 min at 0 °C, maintaining the thermally reversible gelation and mechanical strength of the TRS. Crucially, rheological measurements demonstrate that the viscosity, storage modulus, and loss modulus are not significantly affected by storage in a foam host. This work may be potentially extended to other injectable in situ forming hydrogels, which have suitable mechanical strength but less ideal phase transition times.

Regulation of oil well cement paste properties by nanoclay: Rheology, suspension stability and hydration process

Enhanced grid reconstruction ability of oil well cement paste has been confirmed as a promising solution to inhibit particle sedimentation caused by the uncontrolled rheological property at high temperatures. The effect of nanoclay dispersions of Bentonite and Laponite on the rheological property, suspension stability and hydration process of the cement pastes was examined. The nanoclay dispersions (especially Laponite) enhanced the dynamic reversible gel structure and improved its reconstruction ability. The addition of nanoclay effectively inhibited the sedimentation of solid particles at high temperatures due to form a gel structure by polymer admixtures, nanoclay and cement colloidal particles. Moreover, the nanoclay facilitated the cement hydration and enhanced the mechanical property for the nucleation and filler effect. Accordingly, the nanoclay can enhance thixotropy and suspension stability of the early cement paste and increase the mechanical strength of hardened cement stones, which contributes to improving the sealing integrity of cement sheath.