Polymer Network Density Research Articles

Robust and low swelling polyacrylamide/sodium alginate dual-network hydrogels via multiple freezing strategy toward amphibious motion sensors

The swelling and disintegration behavior of conventional hydrogels in liquid environments significantly affects their mechanical and ionic conductive properties, thereby limiting their widespread application in underwater setting. Herein, we propose a multiple freezing (MF) strategy for the construction of polyacrylamide/sodium alginate (PAM/SA) dual-network hydrogels that exhibit excellent anti-swelling properties and high toughness. The MF strategy employs a combination of freeze casting and refreezing to promote a cascading enhancement of polymer network density, resulting in a highly dense polymer network. This dense network structure endows the hydrogel with impressive tensile strength (3.491 MPa), exceptional elongation at break (435.71 %), and high toughness (5.291 MJ m⁻3), along with remarkable ionic conductivity (142.75 mS m⁻1) and sensitivity (GF = 2.278). These properties enable the hydrogel to function as a flexible sensor capable of detecting various human movement patterns. Its excellent resistance to swelling makes it an ideal material for underwater sensors, effectively monitoring different swimming strokes. This strategy provides a straightforward and effective means to enhance the mechanical strength and adaptability of traditional hydrogels in aquatic environments, demonstrating significant potential for applications in underwater sensing.

Rapid Thermal Shutdown of Deep-Eutectic-Polymer Electrolyte Enabling Overheating Self-Protection of Lithium Metal Batteries.

Safety concerns and uncontrollable dendrite growths have severely impeded the advancement of lithium-metal batteries. Herein, a safe deep-eutectic-polymer electrolyte with built-in thermal shutdown capability is proposed by utilizing hydrophobic association of methylcellulose within a novel deep-eutectic-solvent. Specifically, at elevated temperatures, methylcellulose chains aggregate to form dense polymer networks due to hydrophobic association and break the solvation structure equilibrium inside the deep-eutectic system through encapsulating Li+ in polymer matrix, leading to quick solidification of the electrolyte. The solidified electrolyte obstructs Li+ transports and terminates electrochemical processes, protecting LMBs from unstoppable exothermic chain reactions. The accelerating rate calorimeter tests of 1 Ah pouch cells demonstrate that the as-prepared electrolyte significantly improves the onset self-heating temperature from 73°C for conventional electrolytes to 172°Cand prolongs the thermal runaway waiting time more than 20 hours. More impressively, benefiting from its favorable electrochemical performance, this polymer electrolyte enables LiNi0.8Mn0.1Co0.1O2||Li batteries to retain 92% capacity over 200 cycles and LiFePO4||Li batteries to maintain 90% capacity after 500 cycles. This research paves a promising avenue for enhancing both the safety and electrochemical performance of high-energy-density LMBs.

Sponge-like porous polyvinyl alcohol/chitosan-based hydrogel with integrated cushioning, pH-indicating and antibacterial functions

Developing a packaging material with integrated cushioning, intelligent and active functions is highly desired but remains challenging in the food industry. Here we show that a sponge-like porous hydrogel with pH-indicating and antibacterial additives can meet this requirement. We use polyvinyl alcohol and chitosan as the primary polymers to construct a hydrogel with hierarchical structures through a freeze-casting method in combination with salting-out treatment. The synergy of aggregated polymer chains and the sponge-like porous structure makes the hydrogel resilient and efficient in energy absorption. It also enables rapid movement of molecules/particles and fast reaction due to the large specific surface area of the pore structures and the large amount of free water in it, leading to a sensitive pH-indicating function. The hydrogel shows an obvious color variation within a wide pH range in 3 min. The silver nanoparticles are fixed in the dense polymer networks, enabling a lasting release of silver ions. The porous structure makes the silver ion reach the protected item in a short time, achieving an antibacterial effect against S. aureus and E. coli with little cytotoxicity. This work paves the way for fabricating multifunctional hydrogels for diverse advanced packaging systems.

Flexible bistable polymer stabilised cholesteric texture light shutter display

ABSTRACT Bistable cholesteric liquid crystal displays meet various needs such as energy saving, long image storage time, and no backlight; however, their dense polymer network affects the electro-optical performance. In this work, polymer-stabilised cholesteric texture (PSCT) films with polymer spacer columns were prepared by two-step polymerisation using photomask. The effects of crosslinker content and mask polymerisation time on the morphology of the polymer spacer columns and the optoelectronic properties of the PSCT films were investigated. The results suggested that the film showed bistable performance and the formation of polymer spacer columns helped to optimize the contrast ratio of the sample without sacrificing response time. The cyclic experiment indicated that the optimized bistable PSCT film showed good stability. The adhesion strength of the PSCT film to the substrate was essentially the same as that of commercial PDLC. The simple operability and reusability of the process method make it a practical solution for the preparation of bistable PSCT films.

Unveiling the effect law of carbon dots with polyfunctional groups on interface structure and ion migration in polymer electrolytes for solid lithium battery

Solid polymer electrolyte (SPE) has been considered as promising candidate electrolyte for solid-state lithium metal battery. However, the low ion conductivity and poor interface stability seriously hinder the development of SPE. Introducing the functional filler is a commonly used and effective approach to solving these issues. The poor compatibility and ambiguous mechanism of action are currently the main challenges. In this study, we design and synthesize carbon dots (NSFCDs) with quaternary functional groups, which are introduced into the SPE in the polymerization process of hybrid polymer electrolyte (HPE). The detailed effect law of polyfunctional groups on the polymer chain structure, interface structure of electrolyte/electrode and ion migration is systematically revealed. The dense polymer network endows HPE with enhanced mechanical properties. Through the regulation of polymer segments, the coordination environment of lithium ions is altered, promoting ion transport. The solid electrolyte interface (SEI) induced by NSFCDs and lithium salt anions effectively improves the morphology of lithium ion deposition and alleviates volume strain. As a result, the HPE based on polyethylene oxide (PEO) constructed by free radical polymerization of NSFCDs and polyethylene glycol diacrylate (PEGDA) exhibits excellent comprehensive performance, the assembled Li symmetric battery can cycle stably for 4000 h.

Effect of penetrant-polymer interactions and shape on the motion of molecular penetrants in dense polymer networks.

The diffusion of dilute molecular penetrants within polymers plays a crucial role in the advancement of material engineering for applications such as coatings and membrane separations. The potential of highly cross-linked polymer networks in these applications stems from their capacity to adjust the size and shape selectivity through subtle changes in network structures. In this paper, we use molecular dynamics simulation to understand the role of penetrant shape (aspect ratios) and its interaction with polymer networks on its diffusivity. We characterize both local penetrant hopping and the long-time diffusive motion for penetrants and consider different aspect ratios and penetrant-network interaction strengths at a variety of cross-link densities and temperatures. The shape affects the coupling of penetrant motion to the cross-link density- and temperature-dependent structural relaxation of networks and also affects the way a penetrant experiences the confinement from the network meshes. The attractive interaction between the penetrant and network primarily affects the former since only the system of dilute limit is of present interest. These results offer fundamental insights into the intricate interplay between penetrant characteristics and polymer network properties and also suggest future directions for manipulating polymer design to enhance the separation efficiency.

Novel Furfural-Derived Polyaldimines as Latent Hardeners for Polyurethane Adhesives.

Moisture-curing one-component polyurethane systems in adhesive, sealant, and coating applications may show blister formation upon cure. Blisters can be formed when carbon dioxide, generated in the reaction with isocyanate and water, is trapped in the film. This problem can be mitigated by employing latent hardeners such as blocked polyamines, which are activated upon moisture exposure. The hydrolysis of the latent hardener yields the polyamine that quickly reacts with the isocyanate, forming urea linkages, and then chain extends the polymer. The hydrolysis also releases the blocking agent, which can potentially create an unpleasant odor. In this work, a series of di- and trifunctional aldimines were synthesized from commercially available polyamines, biobased hydroxymethyl furfural, and lauroyl chloride. Hydroxymethyl furfural was first esterified with lauroyl chloride and subsequently condensed with the polyamines to form the aldimines. The application of these novel aldimines in a model moisture-curing system allowed the preparation of blister- and odor-free castings. Based on our results, the mechanical performance of the different aldimines in casting and adhesive applications could be related to the polymer network density. This was dependent on the rate of the aldimine hydrolysis reaction to produce the polyamine. In particular, the use of aldimines prepared from polyether amines and 1,5-diamino-2-methylpentane showed excellent adhesive properties.

Investigation of the Uniformity of Gel Shrinkage by Imaging Tracer Particles Using X‐Ray Microtomography

Mass transfer and structural changes in the polymer matrix need to be understood for a rational optimization of the biopolymer‐based aerogels production. Herein, the uniformity of changes that occur in the gel structure during the aerogel production by a newly developed method which is based on the imaging of metal tracer particles using X‐ray microtomography (X‐ray micro‐CT) alongside the application of point pattern techniques such as the K‐nearest‐neighbor (KNN) distances is studied. Agar is initially used as a system of validation for the developed method, after which other polysaccharide and protein‐based gels such as alginate, whey protein isolate (WPI), and gelatine are studied. The KNN distance is seen to reduce from hydrogel to aerogel. Furthermore, by means of the KNN distances, the biopolymers are observed to experience a nonuniform distribution of tracer particles correlating to nonuniform shrinkage. Densification at specific sites of the gel represented by lower KNN distance values could be distinguished for each biopolymer. Finally, the spatially resolved polymer network density profile is estimated from the KNN distance by correlating it to experimentally determined polymer network density.

Thermally-induced phase fusion and color switching in ionogels for multilevel information encryption

The growing significance of data security has propelled the advancement of information encryption materials. Here, thermochromic poly(4-hydroxybutyl acrylate) (PHBA) ionogels with broad response range and excellent cyclic stability were successfully developed through photopolymerization. Due to the reversible phase diffusion between PHBA polymer networks and ionic liquids (ILs), the PHBA ionogels can switch between opaque and transparent states in response to changes in heating temperature. The enthalpic and entropic properties of the PHBA ionogels were modified by adjusting the crosslinking density (1.0%–2.5%) of polymer networks and concentration (30%-60%) of ILs, which in turn accurately controlled their phase fusion temperature (32 °C to over 68 °C). The size and optical properties of ionogels can be effectively maintained even after exposure to surpass daily ambient temperatures (−10 and 50 °C) or humidity (75%) levels for 12 h, as well as undergoing heating–cooling cycles or operating in ambient environments for 60 days. These findings demonstrate the exceptional stability of these ionogels, rendering them suitable for application as reversible information encryption devices. For the first time, proof-of-concept demonstrations of a thermochromic ionogel system for six-level information encryption and ionogel barcodes are presented here. This work is particularly significant for smart soft materials and information encryption fields.

Inexpensive bioprinting on a microscope using liquid crystal displays and visible light

Patterned photocrosslinking has several uses in the biofabrication of microstructurally complex tissue constructs, through both photolithography of scaffolds and photoconjugation of cell adhesive and instructive moieties. Often the polymers used are modified by methacrylation while photoactivation requires ultraviolet light. In contrast, this study aimed to design, build and evaluate a low-cost platform to place photocrosslink patterns into unmodified collagen and gelatin hydrogels using visible light and ruthenium-mediated tyrosine crosslinking in a way compatible with cell culture and inverted microscopes commonly used in biological laboratories. A photoprinting module was constructed above an inverted microscope sample stage to be confocal with the imaging system. The module consists of a blue light emitting diode array, light pipe, diffuser, microelectronically controlled liquid crystal display as photomask, and focusing objective. Resulting Ruthenium-mediated photocrosslink patterns were visible in unmodified collagen and gelatin hydrogels due to altered local polymer network density and optical contrast. Green fluorescent protein was conjugated in patterns to both gelatin and collagen gels, dependent on light exposure, intensity, and polymer network density. Pattern resolution varied from 2.0 ± 0.5 μm to 102 ± 33 μm (mean ± standard deviation) dependent on the focusing objective magnification and the pattern used (display pixel versus diode element). Further, photocrosslink patterns placed in collagen hydrogels and incubated without rinsing in serum-containing media swelled over 20–48 h, breaking the collagen network and forming ∼50 μm diameter holes. Fibroblasts cultured in photopatterned collagen hydrogels aligned and moved on and around crosslinked regions, consistent with durotaxis and contact guidance. The platform for photocrosslinking described in this study will impact several research fields, notably bioprinting of microstructurally and mechanically complex tissue constructs.

Enhanced Ultra‐Long Room Temperature Phosphorescence by Intermolecular Donor–Acceptor Interaction in Polymer Network

AbstractUltra‐long room temperature phosphorescence (URTP) is an attractive phenomenon in organic photonics. However, most of the reported strategies for enhancing URTP require complicated synthesis processes. Herein, a novel strategy is reported, two birds with one stone, for enhancing URTP by doping the ground‐state intermolecular donor–acceptor complexes into a dense polymer network: i) The dense network ensures the formation of intermolecular donor–acceptor complexes, which provide a smaller singlet‐triplet energy difference (ΔEST) and more intersystem crossing (ISC) channels than the individual donor or acceptor molecules; ii) The dense network adequately suppresses the non‐radiative relaxation caused by molecular vibrations and oxygen quenching. The URTP intensities of the intermolecular donor–acceptor complexes doped film are 20 times higher than that of the film only doped with acceptor molecules, and the phosphorescence lifetime is up to 200 ms. The theoretical calculation reveals the electronic interaction between donor and acceptor and the increased ISC channel, which elucidates the photophysical mechanism of the strategy and confirms its rationality. An advanced encryption application is developed based on enhanced URTP films. This work opens a new direction for URTP materials through the intermolecular donor–acceptor interaction.

How Segmental Dynamics and Mesh Confinement Determine the Selective Diffusivity of Molecules in Cross-Linked Dense Polymer Networks.

The diffusion of molecules ("penetrants") of variable size, shape, and chemistry through dense cross-linked polymer networks is a fundamental scientific problem broadly relevant in materials, polymer, physical, and biological chemistry. Relevant applications include separation membranes, barrier materials, drug delivery, and nanofiltration. A major open question is the relationship between transport, thermodynamic state, and penetrant and polymer chemical structure. Here we combine experiment, simulation, and theory to unravel these competing effects on penetrant transport in rubbery and supercooled polymer permanent networks over a wide range of cross-link densities, size ratios, and temperatures. The crucial importance of the coupling of local penetrant hopping to polymer structural relaxation and the secondary importance of mesh confinement effects are established. Network cross-links strongly slow down nm-scale polymer relaxation, which greatly retards the activated penetrant diffusion. The demonstrated good agreement between experiment, simulation, and theory provides strong support for the size ratio (penetrant diameter to the polymer Kuhn length) as a key variable and the usefulness of coarse-grained simulation and theoretical models that average over Angstrom scale structure. The developed theory provides an understanding of the physical processes underlying the behaviors observed in experiment and simulation and suggests new strategies for enhancing selective polymer membrane design.

Integration of Gold Nanoparticles into Crosslinker-Free Polymer Particles and Their Colloidal Catalytic Property.

This work demonstrates the incorporation of gold nanoparticles (AuNPs) into crosslinker-free poly(N-isopropylacrylamide), PNIPAM, particles in situ and the examination of their structural and catalytic properties. The formation process of the AuNPs across the crosslinker-free PNIPAM particles are compared to that of crosslinked PNIPAM particles. Given the relatively larger free volume across the crosslinker-free polymer network, the AuNPs formed by the in situ reduction of gold ions are detectably larger and more polydisperse, but their overall integration efficiency is slightly inferior. The structural features and stability of these composite particles are also examined in basic and alcoholic solvent environments, where the crosslinker-free PNIPAM particles still offer comparable physicochemical properties to the crosslinked PNIPAM particles. Interestingly, the crosslinker-free composite particles as a colloidal catalyst display a higher reactivity toward the homocoupling of phenylboronic acid and reveal the importance of the polymer network density. As such, the capability to prepare composite particles in a controlled polymer network and reactive metal nanoparticles, as well as understanding the structure-dependent physicochemical properties, can allow for the development of highly practical catalytic systems.

Tough, Transparent, and Slippery PVA Hydrogel Led by Syneresis.

Slippery and transparent polyvinyl alcohol (PVA) hydrogels with mechanical robustness exhibit broad applications in artificial biological soft tissues, flexible wearable electronics, and implantable biomedical devices. Most of the current PVA hydrogels, however, are unable to integrate these features, which compromises its performance in biological and engineering applications. To achieve such purpose, herein, a novel tactic is proposed, salting-out-after-syneresis of PVA, to realize a mechanically robust and highly transparent slippery PVA hydrogel. The syneresis of PVA sol is first conducted to form highly dense and transparent PVA polymer networks, then the salting-out effect tunes the aggregation of the polymer chains to rapidly induce the phase separation and crystallization. The resultant hydrogels show the transparency up to 98% in the visible region, the tribological coefficient down to 0.0081, and the excellent mechanical properties with strength, modulus, and toughness of 26.72±1.05, 6.66±0.29MPa, and 55.21±1.62MJm-3 , respectively. To reveal the potentials, PVA contact lens that combine remarkable lubrication, anti-protein adhesion, biocompatibility, and drug-loading functions are demonstrated. This strategy provides a simple and new avenue for developing the mechanically robust, transparent, and hydrated hydrogels, showing the potential in biomedicine and wearable devices.

Tumor-Targeted Injectable Double-Network Hydrogel for Prevention of Breast Cancer Recurrence and Wound Infection via Synergistic Photothermal and Brachytherapy.

The high locoregional recurrence rate and potential wound infection in breast cancer after surgery pose enormous risks to patient survival. In this study, a polyethylene glycol acrylate (PEGDA)‐alginate double‐network nanocomposite hydrogel (GPA) embedded with 125I‐labeled RGDY peptide‐modified gold nanorods (125I‐GNR‐RGDY) is fabricated. The double‐network hydrogel is formed by injection of GPA precursor solutions into the cavity of resected cancerous breasts of mice where gelation occurred rapidly. The enhanced temperature‐induced PEGDA polymerization driven by near‐infrared light irradiation, and then, the second polymer network is crosslinked between alginate and endogenous Ca2+ around the tumor. The double‐network hydrogel possesses a dense polymer network and tightly fixes 125I‐GNR‐RGDY, which exhibit superior persistent photothermal and radioactive effects. Hyperthermia induced by photothermal therapy can inhibit self‐repair of damaged DNA and promote blood circulation to improve the hypoxic microenvironment, which can synergistically enhance the therapeutic efficacy of brachytherapy and simultaneously eliminate pathogenic bacteria. Notably, this nanocomposite hydrogel facilitates antibacterial activity to prevent potential wound infection and is tracked by single‐photon emission computerized tomography imaging owing to isotope labeling of loaded 125I‐GNR‐RGDY. The combination of photothermal therapy and brachytherapy has enabled the possibility of proposing a novel postoperative adjuvant strategy for preventing tumor recurrence and wound infection.

Correction to “Understanding the Roles of Mesh Size, Tg, and Segmental Dynamics on Probe Diffusion in Dense Polymer Networks”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Understanding the Roles of Mesh Size, Tg, and Segmental Dynamics on Probe Diffusion in Dense Polymer Networks”Grant S. SheridanGrant S. SheridanMore by Grant S. Sheridan and Christopher M. Evans*Christopher M. EvansMore by Christopher M. Evanshttps://orcid.org/0000-0003-0668-2500Cite this: Macromolecules 2022, 55, 12, 5276–5277Publication Date (Web):June 9, 2022Publication History Published online9 June 2022Published inissue 28 June 2022https://doi.org/10.1021/acs.macromol.2c00997Copyright © 2022 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views424Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Structural Relaxation and Vitrification in Dense Cross-Linked Polymer Networks: Simulation, Theory, and Experiment

Structural Relaxation and Vitrification in Dense Cross-Linked Polymer Networks: Simulation, Theory, and Experiment

Selective Recognition of Caffeine by (3-aminopropyl) Triethoxysilane Based Polymers

Background: The metal alkoxides undergo the sol-gel process leads to highly dense polymer networks in nano range size particles. Template-mediated nanomaterial fabrication involves functional monomers, cross binders, catalysis, and other favorable thermal conditions optimized to prepare thermal, mechanical, and chemo-stable tailor-made complimentary recognition sites ceramic materials. Methods: The present study is focused on imprinting of caffeine by sol-gel method, wherein functional monomer as (3-aminopropyl) triethoxysilane (APTES), crosslinker as tetraethyl orthosilicate (TEOS), and ammonium hydroxide solution as catalyst were considered to prepare materials, and those materials characterized. The catalyzed hydrolysis and condensation were carried with a wide range of composition mixtures in acetonitrile optimized at 60 oC. The imprinted polymers (MIPs) and Non-Imprinted Polymers (NIPs) characterized by FTIR, GC-MS, SEM, and EDS techniques. Further post-polymerization studies were carried to investigate recognizing capacity specificity and the binding capacity of the caffeine and its structurally similar analogs with imprinted / non-imprinted polymers. Results: The studies revealed that efficiency in the template removal was high in the imprinted polymers in which low concentration of crosslinker and whereas the selectivity of the template was observed to be high compared with polymers with higher concentrations. Conclusion: In conclusion, high binding affinity was observed in imprinted polymers to that of non- Imprinted polymers.

Precisely Defining Local Gradients of Stimuli-Responsive Hydrogels for Complex 2D-to-4D Shape Evolutions.

The intellectualization and complication of existing self-shaping materials are limited by the inseparable monotonic relationship between their deformation rate and deformation degree (i.e., a higher deformation rate is accompanied by a high deformation degree). This causes that they can only deform from 2D to 3D states. Here, a simple yet versatile strategy to decouple the monotonic correlation between the deformation rate and deformation degree of self-shaping hydrogels is presented for achieving complex deformations from 2D to temporary 3D to 3D (2D-to-4D). It is demonstrated that when the gradient hydrogels prepared by photopolymerization possess dense polymer networks, the local regions with a high deformation rate can exhibit a low deformation degree. The resulting hydrogels can thus deform in a novel 2D-to-4D mode under external stimuli. During the deformation, they first transform into the temporary shapes induced by the local deformation rate difference, and then transform into the final shapes determined by the local deformation degree difference. Through controlling the ultraviolet irradiation direction and time to precisely program the local gradients of self-shaping hydrogels, they can be designed to produce various unprecedented yet controllable 2D-to-4D shape evolutions on demand, such as transformable origami, sequential gesture actions in finger-guessing games, mobile octopuses, time switch, etc.

Heterogeneity and Hysteresis in the Polymer Collapse of Single Core–Shell Stimuli-Responsive Plasmonic Nanohybrids

Broad application of polymeric stimuli-responsive smart nanohybrids requires understanding the mechanisms governing active control. Ensemble techniques have identified inhomogeneous polymer collapse in microgels that potentially arise from heterogeneous interchain interactions and differences in core size. A single-particle examination would establish the influence of core size and internal polymer network heterogeneity on local interactions that contribute to the observed inhomogeneous polymer collapse dynamics of nanohybrids. Using single-particle dark-field spectroscopy, we investigated the complex polymer collapse profiles of core–shell plasmonic nanohybrids comprising thermoresponsive poly(N-isopropylacrylamide) (pNIPAM)-encapsulated gold nanorods (AuNRs). We report that the polymer collapse behavior was independent of the core size. For thinner polymer shells, we observed hysteresis in the collapse of AuNR@pNIPAMs, likely related to local pNIPAM aggregation due to interchain hydrogen bonding. For thicker polymer shells, we observed a broad polymer collapse distribution that we attributed to a two-step phase transition that arises from a polymer network density gradient. Our single-particle approach relates the internal heterogeneity of the polymer network of nanohybrids to the mechanisms underlying heterogeneous phase transitions that traditional, ensemble-averaged approaches are unable to discern.