Cross-linked Polymer Research Articles

Theory of expansion and compression of polymeric materials: Implications for membrane solvent flow under compaction

We extend the classical Flory-Rehner theory for the expansion and compression of porous materials such as cross-linked polymer networks and membranes. The theory includes volume exclusion, affinity with the solvent, and finite stretching of the polymer chains. We also modify this equilibrium theory, which applies to equal expansion of a material in all directions, to the situation where a material can only expand in a single direction, as is the case when a thin polymer layer is tightly bound to a support structure. We further extend this equilibrium model to the case where a pressure is applied across a thin polymer layer, such as a membrane, and liquid flows across the membrane. The theory describes how in the direction of liquid flow the membrane is increasingly compacted and becomes less porous, and this effect increases when the applied pressure goes up. We present results of example calculations for a thick membrane showing significant changes in compaction across its thickness, and a thin membrane where compaction due to flow is minor. Lastly, we model the dynamics of the change in size of a porous material in time after a step change in the solvent-polymer attraction parameter, which may be relevant, for instance, when the attraction parameter is highly temperature-dependent, and we change the temperature. The developed theory has direct implications for pressure-driven membrane separation processes ranging from reverse osmosis to organic solvent nanofiltration.

Construction of a PEGDA/chitosan hydrogel incorporating mineralized copper-doped mesoporous silica nanospheres for accelerated bone regeneration

Hydrogels, integrating diverse biocompatible materials, have emerged as promising candidates for bone repair applications. This study presents a double network hydrogel designed for bone tissue engineering, combining poly(ethylene glycol) diacrylate (PEGDA) and chitosan (CS) crosslinked through UV polymerization and ionic crosslinking. Concurrently, copper-doped mesoporous silica nanospheres (Cu-MSNs) were synthesized using a one-pot method. Cu-MSNs underwent additional modification through in-situ biomineralization, resulting in the formation of an apatite layer. Polydopamine was employed to facilitate the deposition of Calcium (Ca) and Phosphate (P) ions on the surface of Cu-MSNs (Cu-MSNs/PDA@CaP). Composite hydrogels were created by integrating varied concentrations of Cu-MSNs/PDA@CaP (25, 50, 100, 150, 200 μg/mL). Characterization unveiled distinctive interconnected porous structures within the composite hydrogel, showcasing a notable 169.6 % enhancement in compressive stress (elevating from 89.01 to 240.19 kPa) compared to pure PEGDA. In vitro biocompatibility experiments illustrated that the composite hydrogel maintained elevated cell viability (up to 106.6 %) and facilitated rapid cell proliferation over 7 days. The hydrogel demonstrated a substantial 57.58 % rise in ALP expression and a surprising 235.27 % increase in ARS staining. Moreover, it significantly enhanced the expression of crucial osteogenic genes, such as run-related transcription factors 2 (RUNX2), collagen 1a1 (Col1a1), and secreted phosphoprotein 1 (Spp1), establishing it as a promising scaffold for bone regeneration. This study shows how Cu-MSNs/PDA@CaP were successfully integrated into a double network hydrogel, resulting in a composite material with good biological responses. Due to its improved characteristics, this composite hydrogel holds the potential for advancing bone regeneration procedures.

Magneto-Induced Janus Adhesive-Tough Hydrogels for Wearable Human Motion Sensing and Enhanced Low-Grade Heat Harvesting.

Janus hydrogels with different properties on the two surfaces have considerable potential in the field of material engineering applications. Various Janus hydrogels have been developed, but there are still some problems, such as stress mismatch caused by the double-layer structure and Janus failure caused by material diffusion in the gradient structure. Here, we report a Janus adhesive-tough hydrogel with polydopamine-decorated Fe3O4 nanoparticles (Fe3O4@PDA) at one side induced by magnetic field to avoid uncontrollable material diffusion in the cross-linking polymerization of acrylamide with alginate-calcium. The magneto-induced Janus (MIJ) hydrogel has an adhesive surface and a tough bulk without an obvious interface to avoid stress mismatch. Due to the intrinsic dissipative matrix and the abundant catechol groups on the adhesive surface, it shows strong adhesion onto various substrates. The MIJ hydrogel has high sensitivity (GF = 0.842) in detecting tiny human motion. Owing to the synergy of Fe3O4@PDA-enhanced interfacial adhesion and heat transfer, it is possible to quickly generate effective temperature differences when adhering to human skin. The MIJ hydrogel achieves a Seebeck coefficient of 13.01 mV·K-1 and an output power of 462.02 mW·m-2 at a 20 K temperature difference. This work proposes a novel strategy to construct Janus hydrogels for flexible wearable devices in human motion sensing and low-grade heat harvesting.

Molecular engineering of cross-linked polymers based on camphor substituted quinoxaline and 2,5-dithiophen-2-yl-pyrrole for efficient electrochromic energy storage devices

In this work, two donor–acceptor monomers SNSCQH and SNSCQF consisting of two 2,5-dithiophen-2-yl-pyrrole units and camphor substituted quinoxaline-based linkers were developed for electrochromic and energy storage applications. The cross-linked conjugated polymer thin films PSNSCQH and PSNSCQF were successfully prepared through electrochemical polymerization of the corresponding monomers and deposited on ITO substrates, which exhibited remarkable electrochromic performance, involving large optical contrast over 50 %, short response time less than 1.5 s, and high coloration efficiency over 220 cm2/C. Moreover, both PSNSCQH and PSNSCQF demonstrated large areal specific capacitance, with values of 9.27 mF/cm2 and 10.13 mF/cm2 at a current density of 0.1 mA/cm2, respectively. Additionally, electrochromic energy storage devices based on PSNSCQH and PSNSCQF thin films in a sandwich configuration were fabricated, enabling visualization of the energy storage state through color changes. This study provided valuable insights into the behavior of cross-linked two-dimensional conjugated polymers with intermolecular interactions between layers for electrochemical devices.

Selectively Transport and Removal of Fluoride Ion by Pillar[5]Arene Polymer-Filled Nanochannel Membrane.

Excess fluoride ions in groundwater accumulate through the roots of crops, affecting photosynthesis and inhibiting their growth. Long-term bioaccumulation also threatens human health because it is poorly degradable and toxic. Currently, one of the biggest challenges is developing a unique material that can efficiently remove fluoride ions from the environment. The excellent properties of functionalized pillar[5]arene polymer-filled nanochannel membranes were explored to address this challenge. Constructing a multistage porous nanochannel membrane, consisting of microscale etched nanochannels and nanoscale pillar[5]arene cross-linked polymer voids. A fluoride removal rate of 0.0088 mmol ⋅ L-1 ⋅ min-1 was achieved. Notably, this rate surpassed the rates observed with other control ions by a factor of 6 to 8.8. Our research provides a new direction for developing water fluoride ion removal materials.

Facile fabrication of cross-linked polymer electrolyte via imidazole-based deep eutectic solvent-induced in situ polymerizations

Fabricating the cross-linked network is an efficient strategy for improving the mechanical and electrochemical performances of polymer electrolytes (PEs). However, present methods used for the preparation of the cross-linked PEs is difficult to remove the residual catalyst and avoid the side reactions, and the ion conduction in solid PEs is often confined. Herein, we report that the deep eutectic solvent (DES) via the Li–N interaction of 1,2-dimethylimidazole (DMIm) and bis(trifluoromethane)sulfonimide lithium (LiTFSI) displays synergistic effects in inducing the ring-opening polymerization (ROP) of trimethylene carbonate (TMC) and thiol-Michael addition reaction, permitting in situ preparation of PEs with a cross-linked structure. Moreover, DMIm-based DES not only endows PEs with the flame-retardant property but also promotes the conduction of Li ions (Li+) in PEs, leading to a good ionic conductivity at 60 °C (1.8 × 10−4 S cm−1) and Li+ transference number (0.41). Notably, no obvious short-circuit at 0.1 mA cm−2 appears during the deposition process of lithium symmetric batteries assembled with PEs after 1200 h.

ToF-SIMS analysis of ultrathin films and their fragmentation patterns.

Organic thin films are of great interest due to their intriguing interfacial and functional properties, especially for device applications such as thin-film transistors and sensors. As their thickness approaches single nanometer thickness, characterization and interpretation of the extracted data become increasingly complex. In this study, plasma polymerization is used to construct ultrathin films that range in thickness from 1 to 20 nm, and time-of-flight secondary ion mass spectrometry coupled with principal component analysis is used to investigate the effects of film thickness on the resulting spectra. We demonstrate that for these cross-linked plasma polymers, at these thicknesses, the observed trends are different from those obtained from thicker films with lower degrees of cross-linking: contributions from ambient carbon contamination start to dominate the mass spectrum; cluster-induced nonlinear enhancement in secondary ion yield is no longer observed; extent of fragmentation is higher due to confinement of the primary ion energy; and the size of the primary ion source also affects fragmentation (e.g., Bi1 versus Bi5). These differences illustrate that care must be taken in choosing the correct primary ion source as well as in interpreting the data.

Development of Multiple Crosslinked Polymers and Its Application in Synthetic-Based Drilling Fluids.

This study addresses the performance challenges of Synthetic-Based Drilling Fluids (SBDF) in deep wells and high-temperature environments by engineering a novel multiple hydrogen-bonded crosslinked polymer, MBAH/nano-SiO2. Synthesized using methyl methacrylate (MMA), butyl methacrylate (BMA), acrylic acid (AA), N-hydroxyethyl acrylamide (HEAA), and nano-silica (nano-SiO2), the polymer improved crosslinking density, thermal properties, particle size distribution, and colloidal stability. The development of a 'weak gel' structure in W/O emulsions improved rheology and electrical stability (ES), with ES values reaching up to 775 V after aging at 180 °C. Moreover, the polymer's amphiphilic structure and the synergistic effect of nano-SiO2 increased emulsion film thickness and strength, further augmenting stability. The high-temperature and high-pressure filtration loss of SBDF was considerably reduced to 7.6 mL, benefiting well wall stability and reservoir damage control. This study provides crucial insights into optimizing multiple hydrogen-bonded crosslinked strategies and polymers in SBDF applications.

Cross-linked polymer film on copper stubs as a reusable substrate enabling imaging and quantitative analyses of aluminosilicate particles

Access issues to potable waters around the planet is the motivation for research in desalination technologies. One class of materials that is a research focus for desalination membranes are zeolites that are comprised of silicon (Si), aluminum (Al), and oxygen, and have structures that include regular pores of varying sizes dependent on the type of zeolite. A motivation for this study was to enable characterization of non-conductive materials containing Si or Al (e.g., zeolites) using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. To avoid significant background signals directly overlapping with these samples, common sample supports and preparation protocols involving Al or Si were precluded. Cross-linked polymer coatings applied via spin coating onto polished copper (Cu) stubs are shown to be durable for reuse even with the use of aggressive cleaning techniques between samples. SEM and EDS analyses of Cu stubs were performed before and after applying the polymer coating, after drop-cast application of zeolite particles and after their subsequent removal by sonication-based techniques. The data from those trials confirmed there was no background signal from Si or Al and no cross-contamination between samples during these analyses, enabling quantitation of Al and Si in the samples.

Terahertz spectral characteristics of photosensitive resin based on microfluidic technology

Photosensitive resin is a kind of polymer gel material. Due to its excellent UV curing performance, it is widely used in the emerging 3D printing industry. This article combines terahertz technology with microfluidic chip technology to study the terahertz spectral characteristics of liquid and solid photosensitive resins under different electric fields. In the experiment, it was found that an electric field can also cause polymerization of photosensitive resin monomers to form cross-linked polymers, increasing their curing degree. For solid photosensitive resins, the orientation of polymer molecules is enhanced under an electric field, and the molecular arrangement changes from a disordered state to an ordered state. Meanwhile, it was found that both liquid and solid photosensitive resins subjected to electric fields exhibit absorption coefficients below zero within a very small frequency range. We explain this from two aspects: energy and the Fabry Pérot effect. This article uses terahertz spectra to study the curing and structural changes in photosensitive resins under an electric field, laying a foundation for further improving 3D printing technology.

Superabsorbent carboxymethyl cellulose–based hydrogel fabricated by liquid-metal-induced double crosslinking polymerisation

Herein, we introduced a liquid-metal/polymerisable deep eutectic solvent (LM/PDES) system to the carboxymethyl cellulose (CMC) and acrylic acid solution to prepare a double–cross-linked CMC-polyacrylic acid (PAA)-LM/PDES superabsorbent hydrogel via graft crosslinking polymerisation for 5 min. FTIR and XRD provided evidence for the coordinate crosslinking between Ga3+ and carboxy groups in the CMC-PAA-LM/PDES gel structure and chemical crosslinking between CMC and PAA components. The pore size of the obtained hydrogels gradually decreases with the increase of LM-AA/PDES content. The rigid CMC polysaccharide chains increased the distance between the ionic groups on the flexible PAA molecular chains, resulting in high osmotic pressure. In addition, the synergistic effects of hydrophilic groups, electrostatic repulsion, macroporous structures and double crosslinking on the CMC and PAA structures provided a driving force and space for the gel to absorb electrolyte containing liquid. The absorption capacity of the CMC-PAA-LM/PDES gel for physiological saline reached 97 g/g, which exceeded that of a single cross-linked CMC-PAA gel and a reported superabsorbent material (71 g/g). This work solved the problem of long heating times and insufficient mechanical properties for the preparation of superabsorbent gels, providing a theoretical reference for improving the absorption capacity of superabsorbent materials for electrolyte-containing aqueous solutions.

Local Water Content in Polymer Gels Measured with Super-Resolved Fluorescence Lifetime Imaging.

Water molecules play an important role in the structure, function, and dynamics of (bio-) materials. A direct access to the number of water molecules in nanoscopic volumes can thus give new molecular insights into materials and allow for fine-tuning their properties in sophisticated applications. The determination of the local water content has become possible by the finding that H2 O quenches the fluorescence of red-emitting dyes. Since deuterated water, D2 O, does not induce significant fluorescence quenching, fluorescence lifetime measurements performed in different H2 O/D2 O-ratios yield the local water concentration. We combined this effect with the recently developed fluorescence lifetime single molecule localization microscopy imaging (FL-SMLM) in order to nanoscopically determine the local water content in microgels, i.e. soft hydrogel particles consisting of a cross-linked polymer swollen in water. The change in water content of thermo-responsive microgels when changing from their swollen state at room temperature to a collapsed state at elevated temperature could be analyzed. A clear decrease in water content was found that was, to our surprise, rather uniform throughout the entire microgel volume. Only a slightly higher water content around the dye was found in the periphery with respect to the center of the swollen microgels.

Mechanically Triggered Polymer Deconstruction through Mechanoacid Generation and Catalytic Enol Ether Hydrolysis.

Polymers that amplify a transient external stimulus into changes in their morphology, physical state, or properties continue to be desirable targets for a range of applications. Here, we report a polymer comprising an acid-sensitive, hydrolytically unstable enol ether backbone onto which is embedded gem-dichlorocyclopropane (gDCC) mechanophores through a single postsynthetic modification. The gDCC mechanophore releases HCl in response to large forces of tension along the polymer backbone, and the acid subsequently catalyzes polymer deconstruction at the enol ether sites. Pulsed sonication of a 61 kDa PDHF with 77% gDCC on the backbone in THF with 100 mM H2O for 10 min triggers the subsequent degradation of the polymer to a final molecular weight of less than 3 kDa after 24 h of standing, whereas controls lacking either the gDCC or the enol ether reach final molecular weights of 38 and 27 kDa, respectively. The process of sonication, along with the presence of water and the existence of gDCC on the backbone, significantly accelerates the rate of polymer chain deconstruction. Both acid generation and the resulting triggered polymer deconstruction are translated to bulk, cross-linked polymer networks. Networks formed via thiol-ene cross-linking and subjected to unconstrained quasi-static uniaxial compression dissolve on time scales that are at least 3 times faster than controls where the mechanophore is not covalently coupled to the network. We anticipate that this concept can be extended to other acid-sensitive polymer networks for the stress-responsive deconstruction of gels and solvent-free elastomers.

Chromatin phase separated nanoregions explored by polymer cross-linker models and reconstructed from single particle trajectories.

Phase separated domains (PSDs) are ubiquitous in cell biology, representing nanoregions of high molecular concentration. PSDs appear at diverse cellular domains, such as neuronal synapses but also in eukaryotic cell nucleus, limiting the access of transcription factors and thus preventing gene expression. We develop a generalized cross-linker polymer model, to study PSDs: we show that increasing the number of cross-linkers induces a polymer condensation, preventing access of diffusing molecules. To investigate how the PSDs restrict the motion of diffusing molecules, we compute the mean residence and first escaping times. Finally, we develop a method based on mean-square-displacement of single particle trajectories to reconstruct the properties of PSDs from the continuum range of anomalous exponents. We also show here that PSD generated by polymers do not induces a long-range attracting field (potential well), in contrast with nanodomains at neuronal synapses. To conclude, PSDs can result from condensed chromatin organization, where the number of cross-linkers controls molecular access.

Residual alkali-evoked cross-linked polymer layer for anti-air-sensitivity LiNi0.89Co0.06Mn0.05O2 cathode

High-energy density lithium-ion batteries (LIBs) with layered high-nickel oxide cathodes (LiNixCoyMn1−x−yO2, x ≥ 0.8) show great promise in consumer electronics and vehicular applications. However, LiNixCoyMn1−x−yO2 faces challenges related to capacity decay caused by residual alkalis owing to high sensitivity to air. To address this issue, we propose a hazardous substances upcycling method that fundamentally mitigates alkali content and concurrently induces the emergence of an anti-air-sensitive layer on the cathode surface. Through the neutralization of polyacrylic acid (PAA) with residual alkalis and then coupling it with 3-aminopropyl triethoxysilane (KH550), a stable and ion-conductive cross-linked polymer layer is in situ integrated into the LiNi0.89Co0.06Mn0.05O2 (NCM) cathode. Our characterization and measurements demonstrate its effectiveness. The NCM material exhibits impressive cycling performance, retaining 88.4% of its capacity after 200 cycles at 5 C and achieving an extraordinary specific capacity of 170.0 mA h g−1 at 10 C. Importantly, this layer on the NCM efficiently suppresses unfavorable phase transitions, severe electrolyte degradation, and CO2 gas evolution, while maintaining commendable resistance to air exposure. This surface modification strategy shows widespread potential for creating air-stable LiNixCoyMn1−x−yO2 cathodes, thereby advancing high-performance LIBs.

Step-growth Polymerization of Aziridines with Elemental Sulfur: Easy Access to Linear Polysulfides and Their Use as Recyclable Adhesives.

The bulk radical polymerization of bis(aziridine) with molten elemental sulfur resulted in brittle, cross-linked polymers. However, when the bis(aziridine) was treated with elemental sulfur in the presence of an organobase, the ring-opening reaction of aziridine with oligosulfide anions occurred, leading to the formation of linear polymers by step-growth polymerization. These newly synthesized polymers possess repeating units containing a sulfonamide or amide functional moiety and oligosulfide bonds with an average sulfur segment of about two. A small molecular model reaction confirmed the nucleophilic addition reaction of elemental sulfur to aziridine. It was verified that S-S dynamic bond exchange takes place in the presence of an organic base within the linear chains. The mixture of the synthesized polysulfides with pyridine exhibits exceptional adhesive properties when applied to steel, and aluminum substrates. Notably, these prepared adhesives displayed good reusability due to the dynamic S-S exchange and complete recyclability due to their solution processability. This elemental sulfur-involved polymerization approach represents an innovative method for the synthesis of advanced sulfur-containing polymers, demonstrating the potential for various applications in adhesives and beyond.

Development and Application of the Anti-High-Temperature Delayed Crosslinking Polymer as a Gel Plugging Additive for Drilling Fluid.

With the gradual deepening of the exploration and development of deep and ultra-deep oil and gas resources, the problem of lost circulation in drilling operations is becoming more and more complex. From field experience, conventional plugging materials cannot fully meet the technical requirements of plugging operations in drilling engineering. In this study, a high-temperature- and salt-resistant polymer HDZ-A was synthesized. A high-temperature and delayed crosslinking polymer gel plugging agent can be prepared by adding a certain concentration of a crosslinking agent and a retarder. In this paper, the optimum synthesis conditions of the HDZ-A were determined with orthogonal experiments using viscoelasticity and viscosity as evaluation criteria for newly developed polymers. The molecular structure, temperature resistance, and relative molecular mass of HDZ-A were determined using infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. In addition, the optimal formula of the gel plugging agent was determined using gel strength as the evaluation standard. The results show that the newly developed gel plugging agent has stable performance after high-temperature crosslinking, and can resist high temperatures of 160 °C during formation. Under conditions of 160 °C, the gelation time can reach 4.5 h, and the plugging efficiency can reach more than 97%. Finally, the field test of the newly developed high-temperature-resistant delayed crosslinking polymer gel plugging agent was carried out in the direct exploration well KT-14X in the Ordos Basin. The field test showed that the plugging effect of the HDZ-A gel plugging agent was remarkable.

Designing Configurable Soft Microgelsomes as a Smart Biomimetic Protocell.

Self-assembly is an intriguing aspect of primitive cells. The construction of a semipermeable compartment with a robust framework of soft material capable of housing an array of functional components for chemical changes is essential for the fabrication of synthetic protocells. Microgels, loosely cross-linked polymer networks, are suitable building blocks for protocell capsule generation due to their porous structure, tunable properties, and assembly at the emulsion interface. Here, we present an interfacial assembly of microgel-based microcompartments (microgelsomes, MGC) that are defined by a semipermeable, temperature-responsive elastic membrane formed by densely packed microgels in a monolayer. The water-dispersible microgelsomes can thermally shuttle between 10 and 95 °C while retaining their structural integrity. Importantly, the microgelsomes exhibited distinct properties of protocells, such as cargo encapsulation, semipermeable membrane, DNA amplification, and membrane-gated compartmentalized enzymatic cascade reaction. This versatile approach for the construction of biomimetic microcompartments augments the protocell library and paves the way for programmable synthetic cells.

Study on the characteristics of gas phase products in coal mine conveyor belt fire

This study aimed to use the thermogravimetric infrared coupling (TG-FTIR) and cone calorimeter coupling techniques to analyse the Pyrolysis characteristics and fire hazard of conveyor belt during heating process based on different stages of the combustion process. The results demonstrate that the conveyor belt is melted and volatilized by heat in the first stage (200∼350 °C), and a cross-linking polymerization process ensues, with the primary gas-phase products being chlorine-containing compounds, aromatic acid esters, and HCl. In the second stage (350∼600 °C), the conveyor belt started to burn fiercely, redox reactions occurred, the primary gas-phase products added to hydrocarbons, Benzoic acids, aldehydes, amides, and a significant number of CO2, CO, H2O(g). The third stage (600∼700 °C) corresponds to the recession phase of combustion, when the concentration of most gas phase products decreases and the production of amides and ketones increases. As the intensity of thermal radiation increases, the mass loss, heat release rate, fire hazard, CO/CO2 generation rate and smoke also increase.

Tripodal receptor cross-linked polymer as a promising adsorbent for iodine vapor capture and adsorption from water

A cross-linked tripodal receptor polymer was synthesized using a Friedel-Crafts polymerization reaction which showed an iodine vapor capture capacity of 2.47 g g−1 at 80 °C with remarkable iodine adsorption per unit BET surface area of 86 wt/(m2/g). UV–Vis spectral analysis confirmed that the polymer adsorbent rapidly adsorbs iodine from water. Importantly, the polymer exhibited reversible iodine adsorption allowing the polymer to be reused several times without losing the adsorption efficiency. We also investigated the adsorption capability of the synthesized polymer TPP as a filtration material for practical applications. Through dynamic adsorption experiments using a syringe pump setup, we demonstrated that a mere 40 mg of the TPP polymer effectively purifies 20 ml of a 2.5 mM aqueous iodine solution. Our findings underscore the exceptional adsorption efficiency of the TPP polymer, as evidenced by the successful removal of iodine molecules from the solution. These results not only highlight the potential of the TPP polymer for its utility in environmental remediation applications particularly for the treatment of effluents from nuclear reactors.