Crosslinking Density Research Articles

Neuron-inspired CsPbBr3/PDMS nanospheres for multi-dimensional sensing and interactive displays

Multifunctional materials have attracted tremendous attention in intelligent and interactive devices. However, achieving multi-dimensional sensing capabilities with the same perovskite quantum dot (PQD) material is still in its infancy, with some considering it currently challenging and even unattainable. Drawing inspiration from neurons, a novel multifunctional CsPbBr3/PDMS nanosphere is devised to sense humidity, temperature, and pressure simultaneously with unique interactive responses. The carefully engineered polydimethylsiloxane (PDMS) shell enables the reversible activity of the core CsPbBr3, serving a dual role similar to dendrites in conveying and evaluating external stimuli with high sensitivity. Molecular dynamics analysis reveals that the PDMS shell with proper pore density enhances the conductivity in water and heat, imparting CsPbBr3 with sensitive but reversible properties. By tailoring the crosslinking density of the PDMS shell, nanospheres can surprisingly show customized sensitivity and reversible responses to different level of stimuli, achieving over 95% accuracy in multi-dimensional and wide-range sensing. The regular pressure-sensitive property, discovered for the first time, is attributed to the regular morphology of the nanosphere, the inherent low rigidity of the PDMS shell, and the uniform distribution of the CsPbBr3 core material in combination. This study breaks away from conventional design paradigms of perovskite core-shell materials by customizing the cross-linked density of the shell material. The reversible response mechanism of nanospheres with gradient shell density is deeply explored in response to environmental stimuli, which offers fresh insights into multi-dimensional sensing and interactive display applications.

Effects of thiols on electro-optical properties of reverse polymer-stabilised liquid crystal films

ABSTRACT Reverse-mode polymer stabilised liquid crystal (RPSLC) can maintain a transparent state without voltage and exhibit excellent light scattering haze performance when voltage is applied, making it suitable for long-term use in smart windows. However, the high operating voltage of polymer stabilised liquid crystal devices necessitates efforts to reduce the driving voltage and enhance the contrast ratio to improve their optical properties. In this paper, we demonstrate that the introduction of a small amount of the thiol monomer into acrylate polymer monomer during UV-induced homopolymerisation and copolymerisation significantly affects the crosslinking density of the polymer network, thereby influencing the electro-optic performance of RPSLC devices. As a result, we have developed a high-contrast RPSLC device with a saturation voltage below 10 V. These findings are crucial for guiding practical improvements in the performance of RPSLC device.

Construction of Supramolecular Polymer Network Elastomers Based on Pillar[5]arene/Alkyl Chain Host-Guest Interactions.

As a special kind of supramolecular compound with many favorable properties, pillar[n]arene-based supramolecular polymer networks (SPNs) show potential application in many fields. Although we have come a long way using pillar[n]arene to prepare SPNs and construct a series of smart materials, it remains a challenge to enhance the mechanical strength of pillar[n]arene-based SPNs. To address this issue, a new supramolecular regulation strategy was developed, which could precisely control the preparation of pillar[n]arene-based SPN materials with excellent mechanical properties by adjusting the polymer network structures. Specifically, we utilized the host-guest interaction between pillar[5]arene and the alkyl chain of butyl acrylate monomer to form a supramolecular polymer network and achieved the transformation of different states by regulating the cross-linking density of the polymer networks. Additionally, the polymer networks exhibited good stimuli responsiveness as well as excellent dynamic properties and reconfigurable characteristics through a temperature change and the addition of competitive hosts or guests. The research provided new possibilities for the development of polymer materials.

Manifestation of Rouse and Entanglement Dynamics in Non-Cross-Linked and Cross-Linked Polymers Studied by Field-Cycling and Multiple Quantum NMR.

Rubbers prepared from technical poly(butadiene) and natural poly(isoprene) are studied by field-cycling (FC) 1H NMR relaxometry to elucidate the changes of the relaxation spectrum. Starting with the non-cross-linked polymer successively cross-links are introduced via sulfur or peroxide vulcanization. Applying an advanced home-built relaxometer allows one to probe entanglement dynamics in addition to Rouse dynamics. We show that entanglement dynamics evidenced in terms of a characteristic power-law in the NMR susceptibility is still observed with an exponent identical to that in non-cross-linked linear polymers. Yet, the entanglement regime disappears more and more from the accessible frequency window upon increasing the cross-link density and a spectrally enlarged Rouse regime is revealed. Adding a swelling agent, the manifestation of the Rouse and entanglement regimes virtually does not change, yet, the apparent power-law exponents increase. Concomitant multiple-quantum (MQ) 1H NMR experiments provide information on the structure of the rubber network in terms of the residual dipolar coupling and the fraction of the network defects, i.e., persisting entangled or nonentangled chains, introduced upon cross-linking and swelling.

Structure and Functional Characteristics of Novel Polyurethane/Ferrite Nanocomposites with Antioxidant Properties and Improved Biocompatibility for Vascular Graft Development

Novel ferrite/polyurethane nanocomposites were synthesized using the in situ polymerization method after the addition of different spinel nanoferrite particles (copper, zinc, and copper–zinc) and examined as potential coatings for medical devices and implants in vascular tissue engineering. The influence of the nanoferrite type on the structure and functional characteristics of the polyurethane composites was investigated by FTIR, SWAXS, AFM, TGA, DSC, nanoindentation, swelling behavior, water contact angle, and water absorption measurements. Biocompatibility was evaluated by examining the cytotoxicity and adhesion of human endothelial cells and fibroblasts onto prepared composites and performing a protein adsorption test. The antioxidant activity was detected by UV–VIS spectroscopy using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay. Embedding the different types of nanoparticles in the polyurethane matrix increased phase mixing, swelling ability, and DPPH scavenging, decreased surface roughness, and differently affected the stiffness of the prepared materials. The composite with zinc ferrite showed improved mechanical properties, hydrophilicity, cell adhesion, and antioxidant activity with similar thermal stability, but lower surface roughness and crosslinking density compared to the pristine polyurethane matrix. The in vitro biocompatibility evaluation demonstrates that all nanocomposites are non-toxic, exhibit good hemocompatibility, and promote cell adhesion, and recommends their use as biocompatible materials for the development of coatings for vascular implants.

Surface Hydration and Antifouling Activity of Coatings of Polymers and Their Zwitterionic Derivatives Prepared Using Initiated Chemical Vapor Deposition (iCVD).

Sum frequency generation vibrational spectroscopy was applied to study the surface hydration and protein adsorption behavior on several polymer coatings based on pyridine, imidazole, and amine side groups along with vinyl or methacrylate backbones and their corresponding zwitterionic forms with carboxybetaine or sulfobetaine side chains, prepared by initiated chemical vapor deposition (iCVD). iCVD also enables facile tuning of the cross-linking density of the polymer coatings by blending in a cross-linker during the deposition, namely, 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane. Our results show that both the low- and high-cross-linking density zwitterionic polymers exhibit significantly better antifouling activities compared to those of the polymers without the zwitterionic side chains. The weak hydration signals from the low-density zwitterionic polymer/water interfaces were caused by the permeation of the polymer layer by water. The iCVD method is a widely applicable methodology to prepare zwitterionic polymer coatings with an excellent antifouling property.

Full-Spectrum Mechanochromic Photonic Films with Large Interparticle Distance.

Non-close-packed crystalline arrays of colloidal particles in an elastic matrix exhibit mechanochromism. However, small interparticle distances often limit the range of reversible color shifts and reduce reflectivity during a blueshift. A straightforward, reproducible strategy using matrix swelling to increase interparticle distance and improve mechanochromic performance is presented. Photonic composites are initially prepared with silica particle arrays embedded in an elastomer matrix at volume fractions of 0.35-0.5. To increase interparticle distance, the composites are immersed in an elastomer-forming monomer, causing the matrix to swell, followed by photopolymerization, thereby producing liquid-free composites. The degree of swelling is controllable up to 3.16, depending on monomer choice, matrix volume fraction, and crosslinking density. The process can be repeated to further increase swelling up to 10.36. This method can reduce the volume fraction of silica particles from 40% to 3.8%, while interparticle distance increases from 53 to 257nm. The swollen photonic composites exhibit a full visible spectrum under compression, while minimizing reflectivity loss. This allows red-colored photonic composites to be transformed into vivid multicolor patterns when compressed with stamps featuring spatial height variations.

Yellow fluorescent UV-curable epoxy acrylate/VTMS-modified GQDs coatings: study of UV-blocking and viscoelastic properties

Polymer coatings decompose in the presence of UV radiation from sunlight and beget economic and environmental losses. Hence, it is necessary to reinforce the polymer coatings with UV-blocking nanoparticles and to convert the UV light into visible light. In this research work, the surface of graphene quantum dots (GQDs) was modified by vinyltrimethoxysilane (VTMS). VTMS-modified GQDs (VmGQDs) including 0, 0.3 and 0.6 wt% were taken into account to synthesize UV-curable epoxy acrylate/VmGQDs (Ep/VmGQDs) nanocomposite coatings. Surface modification, UV-blockage, fluorescence features and viscoelastic properties of Ep/VmGQDs coatings were analyzed by various spectrometry tests. The existence of VmGQDs (0.3 wt% and 0.6 wt%) in the polymer matrix led to absorption of UV rays in UV regions and fluorescence emission in the visible area with 578 nm wavelength (yellow fluorescence). Appearance of strong absorption bands at 250, 285 and 365 nm by the coatings with VmGQDs confirmed that a large portion of UV rays was absorbed and blocked. The intensity of UV-blockage by Ep/VmGQDs 0.6 wt% was recorded >99%. Furthermore, reinforcement of the coatings with VmGQDs resulted in increase in storage modulus, cross-linking density and Tg value.

Optimizing the charge transport in redox-active gels: a computational study.

Redox-active polymer gels are promising materials for various applications, such as energy conversion and storage systems, organic electronics, soft-robotics, sensors and others. This is in part due to the remarkable structural tunability of these materials. The gel may adopt different conformations depending on the crosslinking density, solvent temperature and other conditions. These parameters affect its behavior, including the dynamics of the charge transport between the redox groups grafted to the polymer subchains, which is of utmost importance for electrochemical applications. Here, we employed coarse-grained molecular dynamics simulation to investigate the impact of crosslinking, redox group content and solvent quality on both subchain mobility and charge transport speed. In particular, unexpected behavior of the system under the theta-solvent condition was found and analyzed. The obtained results provide useful guidelines to facilitate the best conditions for enhanced "redox induced" conductivity in polymer gels, which would help the development of redox-flow batteries and other electrochemical devices.

Pullulan fermented by Aureobasidium melanogenum TZ-FC3 for the preparation of self-healing, adhesive, injectable and antibacterial pullulan/PVA/borax hydrogel.

Natural polymer hydrogels, such as pullulan-based hydrogels, offer significant advantages over synthetic materials due to their thermal stability, film-forming capacity, solubility, adhesiveness, and antioxidant properties. In this study, the strain Aureobasidium melanogenum TZ-FC3, which produces a high level of pullulan, was successfully isolated from the mangrove ecosystems of Guangdong Province, China. 66.01 ± 1.10 g/L pullulan without melanin was produced by the TZ-FC3 strain within 120 h at flask level. Pullulan fermented by A. melanogenum TZ-FC3 was added to enhance the hydrogen bond network within the pullulan/PVA/borax hydrogels (P-2, P-3 and P-4 hydrogels) to improve mechanical strength and crosslinking density of PVA/borax hydrogel (P-1 hydrogel). Compared to the P-1 hydrogel, the P-2 hydrogel exhibited a 65.4 % increase in tensile strain, a remarkable 694.03 % increase in tensile strength and improved the degree of internal crosslinking. Additionally, the pullulan/PVA/borax hydrogels demonstrated excellent self-healing properties, adhesion, injectability, and antibacterial activity. The preparation process of pullulan/PVA/borax hydrogels is straightforward and effective, suggesting broad industrial applicability and underscoring their potential as next-generation materials for advanced healthcare solutions.

Photodegradable polyacrylamide tanglemers enable spatiotemporal control over chain lengthening in high-strength and low-hysteresis hydrogels.

Covalent hydrogel networks suffer from a stiffness-toughness conflict, where increased crosslinking density enhances the modulus of the material but also leads to embrittlement and diminished extensibility. Recently, strategies have been developed to form highly entangled hydrogels, colloquially referred to as tanglemers, by optimizing polymerization conditions to maximize the density and length of polymer chains and minimize the crosslinker concentration. It is challenging to assess entanglements in crosslinked networks beyond approximating their theoretical contribution to mechanical properties; thus, in this work, we synthesize and characterize polyacrylamide tanglemers using a photolabile crosslinker, which allows for direct assessment of covalent trapping of entanglements under tension. Further, this chemistry allows tuning of the modulus in situ by crosslink photocleavage (from tensile modulus (ET) = 100 kPa to <25 kPa). Beyond cleavage of crosslinks, we demonstrate that even non-degradable tanglemer formulations can be photo-softened and completely degraded through Fe3+-mediated oxidation of the polyacrylamide backbone. While both photodegradation methods are useful for spatial patterning and result in softer gels with reduced fracture strength, only crosslink photocleavage improves gel extensibility via light-induced chain lengthening (εF = 700% to >1500%). Crosslink photocleavage in tanglemers also affords significant control over localized swelling and diffusivity. In sum, we introduce a simple and user-directed approach for probing entanglements and asserting spatiotemporal control over stress-strain responses and small molecule diffusivity in polyacrylamide tanglemers, suggesting a multitude of potential soft matter applications including controlled release and tunable bioadhesive interfaces.

Boundaries and cross-link densities modulate domain sizes of polydomain nematic elastomers

Nematic liquid crystal elastomers (LCEs) crosslinked at their isotropic phase, when they are quenched to the nematic phase, show polydomain patterns, in which nematic microdomains with different orientations self-organize into...

Acrylamide/Alyssum campestre seed gum hydrogels enhanced with titanium carbide: Rheological insights for cardiac tissue engineering.

This study investigates the use of acrylamide and Alyssum campestre seed gum (ACSG) to create hydrogel composites with enhanced electrical and mechanical properties by incorporating titanium carbide (TiC). The composites were analyzed through techniques such as FTIR, SEM, TEM, TGA, swelling, rheology, tensile, electrical conductivity, antibacterial, and MTT assays. XRD analysis showed that 0.5 % TiC NPs were exfoliated in the hydrogel, while 1 % was intercalated. SEM images showed that ACSG created a semi-interpenetrating polymer network with interconnected cavities averaging 9.1 μm, which reduced to 3.6 μm with 0.5%TiC and 51.8 nm with 1%TiC due to increased crosslinking density. TGA results confirmed hydrogel stability at autoclave temperatures. Rheological testing revealed that the hydrogel exhibited a maximum resistance of 317 kPa. The addition of 1 % TiC enhanced its electrical conductivity to 1.5 × 10-2S/cm, making it suitable for applications in cardiac tissue engineering. MTT assays confirmed the hydrogel's biocompatibility and demonstrated its superior antibacterial activity against Staphylococcus aureus compared to Escherichia coli. The AM/ACSG/TiC hydrogel is a promising material for cardiac tissue engineering because of its adjustable mechanical properties, excellent electrical conductivity, and strong compatibility with cell cultures. The addition of ACSG improves the hydrogel's rheological behavior, which is crucial for promoting effective cell growth.

Mucoadhesive Enhancement of Gelatine by Tannic Acid Crosslinking for Buccal Application

ABSTRACTThis study aims to evaluate the impact of formulation parameters on tannic acid‐crosslinked gelatine (GelTA) films, intended as a mucoadhesive matrix for extended buccal drug delivery. GelTA films were prepared using the solvent evaporation technique and screened based on their mucoadhesive and dissolution characteristics. The formulation variables included the source of gelatine (bovine and fish), tannic acid concentration, pH of the film‐forming solutions, and the type and concentration of plasticisers. Subsequently, selected films underwent further characterisation (e.g., crosslinking density, stability) to elucidate their features as a drug delivery matrix. GelTA films exhibited a significantly improved dissolution time compared to the non‐crosslinked film (BG‐GLY20), while maintaining a substantial water uptake capacity conducive to a matrix system with extended action. The bovine GelTA film containing 5% w/w tannic acid and 20% w/w glycerine, prepared at pH 7 (BG‐GLY20‐7), exhibited a 1.6‐fold increase in mucoadhesivity and an extended dissolution time of up to 6 h compared to BG‐GLY20 (control), along with superior antioxidant and antimicrobial properties. However, stability studies indicate the need for an oxygen‐free environment for film storage. In conclusion, GelTA films show promise as a buccal film matrix, offering extended dissolution times, substantial water uptake, and enhanced adhesive strength.

Effect of curing process on the structure and properties of paper-based friction materials

As one of the three main components of paper-based friction materials, resin plays a crucial role in determining the material’s performance. Resin behavior varies under different curing conditions, affecting its properties and the overall performance of the material. To find the optimal curing process for paper-based friction materials, we studied the curing process and mechanism of polyamide-modified phenolic resin (PA–PF composite resin) and examined how the curing process influences the structure and properties of these materials. The findings indicate that paper-based friction materials cured at 160°C for 60 minutes show the highest fiber/resin interface bonding strength, with a tensile strength of 14.4 MPa, shear strength of 1.3 MPa, and a strength retention rate of 99.2% after reaching a stable permanent deformation rate. These materials also demonstrate stable dynamic mechanical thermal performance, including a storage modulus of 2758.6 MPa, a cross-linking density of 146343 mol/m³, and a glass transition temperature of 205.7°C. Furthermore, they have excellent compression resilience, with a low permanent deformation rate of 4.1%, and show a uniform pore distribution with a porosity rate of 57.1%. The wear rate is measured at 0.3 × 10−8 cm³/N · m, and the average dynamic friction coefficients are 0.3, 0.1, and 0.1 at pressures of 0.5 MPa, 1.9 MPa, and 3.0 MPa, respectively, with dynamic/static friction coefficient ratios of 0.9, 0.9, and 0.8.

Water Uptake, Thin-Film Characterization, and Gravimetric pH-Sensing of Poly(vinylphosphonate)-Based Hydrogels.

Herein, novel, superabsorbent, and pH-responsive hydrogels obtained by the photochemical cross-linking of hydrophilic poly(vinylphosphonates) are introduced. First, statistical copolymers of diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP) are synthesized via rare earth metal-mediated group-transfer polymerization (REM-GTP) yielding similar molecular weights (Mn,NMR = 127-142 kg/mol) and narrow polydispersities (Đ < 1.12). Subsequently, polymer analogous transformations of P(DEVP-stat-DAlVP) introduced vinylphosphonic acid (VPA) units into the polymers. In this context, the partial dealkylation of the polymers revealed a preference for DAlVP hydrolysis, which was observed via 1H NMR spectroscopy and explained mechanistically. Furthermore, the P(DEVP-stat-DAlVP-stat-VPA) polymers were cross-linked under photochemical reaction conditions (λ = 365 nm) via thiol-ene click chemistry, yielding superabsorbent hydrogels with water uptakes up to 150 ± 27 g (H2O)/g (hydrogel). Regarding water absorption, evident structure-property relationships between cross-linking density, polarity, and swelling behavior were found. Finally, the pH-responsiveness of thin films of these hydrogels was investigated. In this regard, films with a thickness of 39.4 ± 2.33 nm determined via profilometry were spin-coated on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D) and thoroughly characterized by atomic force microscopy (AFM). QCM-D measurements exposing the hydrogel films to different aqueous media revealed different swelling states of the hydrogels depending on the pH values (1, 6, 10, and 13) of the surrounding environment, as reflected by corresponding frequency and dissipation values. The hydrogels exhibited fully reversible swelling and deswelling upon switching between pH 1 and 13 (three cycles), sustaining the harsh conditions without erosion from the gold surface and thus acting as a gravimetric sensor discriminating between the two pH values. The high stability of the films on the gold surfaces of QCM-D sensors was explained by anchoring of the P(DEVP-stat-DAlVP-stat-VPA) networks through the dithiol cross-linker as confirmed by detailed X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies.

An Ultra-Stable Polysaccharide Gel Plugging Agent for Water Shutoff in Mature Oil Reservoirs

Polyacrylamide-based gel plugging agents are extensively utilized in oilfields for water shutoff. However, their thermal stability, salt tolerance, and shear resistance are limited, making it difficult to achieve high-strength plugging and maintain stability under high-temperature and high-salinity reservoir conditions. This study proposes the use of chitosan (CTSs), a polysaccharide with a rigid cyclic structure, as the polymer. The organic cross-linker N,N’-methylenebisacrylamide (MBA) is incorporated via the Michael addition reaction mechanism to develop an ultra-stable, organically cross-linked chitosan gel system. The CTS/MBA gel system was evaluated under various environmental conditions using rheological testing and thermal aging to assess gel strength and stability. The results demonstrate significant improvements in gel strength and stability at high temperatures (up to 120 °C) and under high-shear conditions, as the increased cross-linking density enhanced resistance to thermal and mechanical degradation. Rapid gelation was observed with increasing MBA concentration, while pH and salinity further modulated gel properties. Scanning electron microscopy revealed the formation of a three-dimensional microstructure after gelation, which contributed to the enhanced properties. This study provides novel insights into optimizing polymer gel performance for the petroleum industry, particularly in high-temperature and high-shear environments.

Enhancing the Gas Transport Properties of Network Polyimide Membranes by Reducing Cross-Linking Density and Thermal Treatment

Enhancing the Gas Transport Properties of Network Polyimide Membranes by Reducing Cross-Linking Density and Thermal Treatment

Interpenetrating Network Strategy for Highly Effective Toughening of Epoxy Resin Using Cellulose Microgels

AbstractEpoxy resin (EP) is widely used in coatings, adhesives, and molding materials. EP's high crosslinking density provides a strong modulus but also leads to reduced elongation at break and lower toughness. In this study, bacterial cellulose microgel (BC‐M) is employed to toughen EP through in situ polymerization, to form an interpenetrating network with EP. Bacterial cellulose nanofibers (BC‐CNF) and ethylated bacterial cellulose microgels (EM) are used as controls to highlight the advantages of the 3D network in enhancing polymer toughness. BC‐M demonstrates the most effective toughening performance for EP. At a filler content of 0.3 wt.%, BC‐M/EP nanocomposites exhibite significant improvements in mechanical properties, including a fracture strength of 107.8 MPa, strain of 3.53%, Young's modulus of 3.09 GPa, and toughness of 1.98 kJ m−3. Compared to EP, these values represent enhancements of 40%, 9.5%, 27.3%, and 58.4%, respectively. Comparisons with BC‐CNF/EP and EM/EP nanocomposites clearly demonstrate that BC‐M provided superior toughening effects. The exceptional toughening capability of BC‐M is attributed to its 3D network structure, which effectively dissipates applied energy, and its strong interfacial interaction with the epoxy matrix through covalent bonding.

Study on the Curing Behaviors of Benzoxazine Nitrile-Based Resin Featuring Fluorene Structures and the Excellent Properties of Their Glass Fiber-Reinforced Laminates.

Benzoxazine and o-phthalonitrile resin are two of the most eminent polymer matrices within high-performance fiber-reinforced resin-based composite materials. Studying the influence modalities of their structures and forming processes on performance can furnish a theoretical basis for the design and manufacturing of superior performance composite materials. In this study, we initially incorporated a fluorene structure into the molecular main chain through molecular design to prepare a fluorene-containing benzoxazine nitrile-based resin. The polymerization reaction behavior and process of this resin were monitored meticulously using differential scanning calorimetry and infrared spectroscopy. Meanwhile, by manipulating the pre-polymerization reaction conditions, the impact of the pre-polymerization reaction on the polymerization behavior of the resin monomer was investigated, respectively. Subsequently, diverse glass fiber-reinforced resin-based composite materials were fabricated via hot-pressing in combination with a programmed temperature rise process. Through the characterization of structural strength and thermomechanical properties, it was found that the composite laminates all manifested outstanding bending strength (~600 MPa) and modulus (>30 GPa). Nevertheless, with the elevation of the post-curing temperature, the structural strength and modulus of the composite materials displayed distinct variation laws. This study also discussed the variation laws of the thermal properties of the composite materials by analyzing the glass transition temperature and crosslinking density. Additionally, the interface bonding effect between the glass fiber and the resin matrix was deliberated through the analysis of the cross-sectional morphology of the composite laminates. The results demonstrated that this work proposes an improved matrix resin system with outstanding thermal stability and mechanical properties that broadens the foundation and ideas for subsequent research.