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Understanding the physical principle that governs the stimuli-induced swelling and shrinking kinetics of hydrogels is indispensable for their applications. Here, we show that the shrinking and swelling kinetics of self-healing hydrogels could be intrinsically asymmetric. The structure frustration, formed by the large difference in the heat and solvent diffusions, remarkably slows down the shrinking kinetics. The plateau modulus of viscoelastic gels is found to be a key parameter governing the formation of structure frustration and, in turn, the asymmetric swelling and shrinking kinetics. This work provides fundamental understandings on the temperature-triggered transient structure formation in self-healing hydrogels. Our findings will find broad use in diverse applications of self-healing hydrogels, where cooperative diffusion of water and gel network is involved. Our findings should also give insight into the molecular diffusion in biological systems that possess macromolecular crowding environments similar to self-healing hydrogels.
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Hidrogeles , Temperatura , Difusión , Hidrogeles/química , Cinética , Agua/químicaRESUMEN
Soil salinization is a major abiotic factor threatening rapeseed yields and quality worldwide, yet the adaptive mechanisms underlying salt resistance in rapeseed are not clear. Therefore, this study aimed to explore the differences in growth potential, sodium (Na+) retention in different plant tissues, and transport patterns between salt-tolerant (HY9) and salt-sensitive (XY15) rapeseed genotypes, which cultivated in Hoagland's nutrient solution in either the with or without of 150 mM NaCl stress. The results showed that the inhibition of growth-related parameters of the XY15 genotype was higher than those of the HY9 in response to salt stress. The XY15 had lower photosynthesis, chloroplast disintegration, and pigment content but higher oxidative damage than the HY9. Under NaCl treatment, the proline content in the root of HY9 variety increased by 8.47-fold, surpassing XY15 (5.41-fold). Under salt stress, the HY9 maintained lower Na+ content, while higher K+ content and exhibited a relatively abundant K+/Na+ ratio in root and leaf. HY9 also had lower Na+ absorption, Na+ concentration in xylem sap, and Na+ transfer factor than XY15. Moreover, more Na+ contents were accumulated in the root cell wall of HY9 with higher pectin content and pectin methylesterase (PME) activity than XY15. Collectively, our results showed that salt-tolerant varieties absorbed lower Na+ and retained more Na+ in the root cell wall (carboxyl group in pectin) to avoid leaf salt toxicity and induced higher proline accumulation as a defense and antioxidant system, resulting in higher resistance to salt stress, which provides the theoretical basis for screening salt resistant cultivars.
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Brassica napus , Genotipo , Prolina , Estrés Salino , Tolerancia a la Sal , Sodio , Prolina/metabolismo , Brassica napus/genética , Brassica napus/efectos de los fármacos , Brassica napus/metabolismo , Brassica napus/fisiología , Sodio/metabolismo , Estrés Salino/genética , Tolerancia a la Sal/genética , Hojas de la Planta/metabolismo , Hojas de la Planta/genética , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/fisiología , Raíces de Plantas/metabolismo , Raíces de Plantas/genética , Raíces de Plantas/fisiología , Raíces de Plantas/efectos de los fármacos , Cloruro de Sodio/farmacología , Fotosíntesis/efectos de los fármacos , Potasio/metabolismoRESUMEN
Tough and self-healing hydrogels are typically sensitive to loading rates or temperatures due to the dynamic nature of noncovalent bonds. Understanding the structure evolution under varying loading conditions can provide valuable insights for developing new tough soft materials. In this study, polyampholyte (PA) hydrogel with a hierarchical structure is used as a model system. The evolution of the microscopic structure during loading is investigated under varied loading temperatures. By combining ultra-small angle X-ray scattering (USAXS) and Mooney-Rivlin analysis, it is elucidated that the deformation of bicontinuous hard/soft phase networks is closely correlated with the relaxation dynamics or strength of noncovalent bonds. At high loading temperatures, the gel is soft and ductile, and large affine deformation of the phase-separated networks is observed, correlated with the fast relaxation dynamics of noncovalent bonds. At low loading temperatures, the gel is stiff, and nonaffine deformation occurs from the onset of loading due to the substantial breaking of noncovalent bonds and limited chain mobility as well as weak adaptation of phase deformation to external stretch. This work provides an in-depth understanding of the relationship between structure and performance of tough and self-healing hydrogels.
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Tough soft materials usually show strain softening and inelastic deformation. Here, we study the molecular mechanism of abnormally large nonsoftening, quasi-linear but inelastic deformation in tough hydrogels made of hyperconnective physical network and linear polymers as molecular glues to the network. The interplay of hyperconnectivity of network and effective load transfer by molecular glues prevents stress concentration, which is revealed by an affine deformation of the network to the bulk deformation up to sample failure. The suppression of local stress concentration and strain amplification plays a key role in avoiding necking or strain softening and endows the gels with a unique large nonsoftening, quasi-linear but inelastic deformation.
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As a key component in laminated glass, plasticized polyvinyl butyral (PVB) interlayer is a kind of impact-resistant polymer material with high toughness. Recently, by using ultrasmall angle X-ray scattering (USAXS) technique, Stretch-induced phase-separated structure on the scale of hundreds of nanometers formed in plasticized PVB for the first time is reported. In this work, the multiscale relaxation behavior of plasticized PVB is further investigated. The relaxation behavior of deformed plasticized PVB is studied from macroscopic stress, mesoscopic phase-separated structure, and microscopic chain segment by combining USAXS, and birefringence with in situ stretching device. The contributions of chain segments and hydrogen bonding clusters for the multiscale relaxation behavior are discussed.
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Cloruro de Polivinilo , Polivinilos , Polivinilos/química , Polímeros/química , Enlace de HidrógenoRESUMEN
The memory of our brain, stored in soft matter, is dynamic, and it forgets spontaneously to filter unimportant information. By contrast, the existing manmade memory, made from hard materials, is static, and it does not forget without external stimuli. Here we propose a principle for developing dynamic memory from soft hydrogels with temperature-sensitive dynamic bonds. The memorizing-forgetting behavior is achieved based on fast water uptake and slow water release upon thermal stimulus, as well as thermal-history-dependent transparency change of these gels. The forgetting time is proportional to the thermal learning time, in analogy to the behavior of brain. The memory is stable against temperature fluctuation and large stretching; moreover, the forgetting process is programmable. This principle may inspire future research on dynamic memory based on the nonequilibrium process of soft matter.
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Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G0 above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition Gtran far above G0 In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and Gtran corresponds to the rupture of the hard phase network.
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The general aspects of polymer crystallization under external flow, i.e., flow-induced crystallization (FIC) from fundamental theoretical background to multi-scale characterization and modeling results are presented. FIC is crucial for modern polymer processing, such as blowing, casting, and injection modeling, as two-third of daily-used polymers is crystalline, and nearly all of them need to be processed before final applications. For academics, the FIC is intrinsically far from equilibrium, where the polymer crystallization behavior is different from that in quiescent conditions. The continuous investigation of crystallization contributes to a better understanding on the general non-equilibrium ordering in condensed physics. In the current review, the general theories related to polymer nucleation under flow (FIN) were summarized first as a preliminary knowledge. Various theories and models, i.e., coil-stretch transition and entropy reduction model, are briefly presented together with the modified versions. Subsequently, the multi-step ordering process of FIC is discussed in detail, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline. These achievements for a thorough understanding of the fundamental basis of FIC benefit from the development of various hyphenated rheometer, i.e., rheo-optical spectroscopy, rheo-IR, and rheo-x-ray scattering. The selected experimental results are introduced to present efforts on elucidating the multi-step and hierarchical structure transition during FIC. Then, the multi-scale modeling methods are summarized, including micro/meso scale simulation and macroscopic continuum modeling. At last, we briefly describe our personal opinions related to the future directions of this field, aiming to ultimately establish the unified theory of FIC and promote building of the more applicable models in the polymer processing.
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A finite strain nonlinear viscoelastic constitutive model is used to study the uniaxial tension behaviour of chemical polyampholyte (PA) gel. This PA gel is cross-linked by chemical and physical bonds. Our constitutive model attempts to capture the time and strain dependent breaking and healing kinetics of physical bonds. We compare model prediction by uniaxial tension, cyclic and relaxation tests. Material parameters in our model are obtained by least squares optimization. These parameters gave fits that are in good agreement with the experiments.
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Flow-induced crystallization (FIC) is a typical nonequilibrium phase transition and a core industry subject for the largest group of commercially useful polymeric materials: semicrystalline polymers. A fundamental understanding of FIC can benefit the research of nonequilibrium ordering in matter systems and help to tailor the ultimate properties of polymeric materials. Concerning the crystallization process, flow can accelerate the kinetics by orders of magnitude and induce the formation of oriented crystallites like shish-kebab, which are associated with the major influences of flow on nucleation, that is, raised nucleation density and oriented nuclei. The topic of FIC has been studied for more than half a century. Recently, there have been many developments in experimental approaches, such as synchrotron radiation X-ray scattering, ultrafast X-ray detectors with a time resolution down to the order of milliseconds, and novel laboratory devices to mimic the severe flow field close to real processing conditions. By a combination of these advanced methods, the evolution process of FIC can be revealed more precisely (with higher time resolution and on more length scales) and quantitatively. The new findings are challenging the classical interpretations and theories that were mostly derived from quiescent or mild-flow conditions, and they are triggering the reconsideration of FIC foundations. This review mainly summarizes experimental results, advances in physical understanding, and discussions on the multiscale and multistep nature of oriented nuclei induced by strong flow. The multiscale structures include segmental conformation, packing of conformational ordering, deformation on the whole-chain scale, and macroscopic aggregation of crystallites. The multistep process involves conformation transition, isotropic-nematic transition, density fluctuation (or phase separation), formation of precursors, and shish-kebab crystallites, which are possible ordering processes during nucleation. Furthermore, some theoretical progress and modeling efforts are also included.
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Understanding the energy dissipation mechanism during deformation is essential for the design and application of tough soft materials. We show that, in a class of tough and self-healing polyampholyte hydrogels, a bicontinuous network structure, consisting of a hard network and a soft network, is formed, independently of the chemical details of the hydrogels. Multiscale internal rupture processes, in which the double-network effect plays an important role, are found to be responsible for the large energy dissipation of these hydrogels.
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Recently, we have developed a series of charge balanced polyampholyte (PA) physical hydrogels by random copolymerization in water, which show extraordinarily high toughness, self-healing ability and viscoelasticity. The excellent performance of PA hydrogels is ascribed to dynamic ionic bond formation through inter- and intra-chain interactions. The randomness results in ionic bonds of wide strength distribution, the strong bonds, which serve as permanent crosslinking, imparting the elasticity, while the weak bonds reversibly break and re-form, dissipating energy. In this work, we developed a simple physical method, called a pre-stretching method, to promote the performance of PA hydrogels. By imposing a pre-stretching on the sample in the as-prepared state, ion complexation during dialysis is prominently accelerated and the final performance is largely promoted. Further analysis suggests that the strong bond formation induced by pre-stretching is responsible for the change in final performance. Pre-stretching decreases the entropy of the system and increases the chain alignment, resulting in an increased possibility for strong bond formation.
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Soil arsenic (As) phytoremediation has long faced the challenge of efficiently absorbing As by plant accumulators while maintaining their health and fast growth. Even at low doses, arsenic is highly toxic to plants. Therefore, plant growth-promoting microorganisms that can mediate As accumulation in plants are of great interest. In this study, the endophyte Enterobacter sp. YG-14 (YG-14) was found to have soil mobilization activity. By constructing a siderophore synthesis gene deletion mutant (ΔentD) of YG-14, the endophyte was confirmed to effectively mobilize Fe-As complexes in mining soil by secreting enterobactin, releasing bioavailable Fe and As to the rhizosphere. YG-14 also enhances As accumulation in host plants via extracellular polymer adsorption and specific phosphatase transfer protein (PitA) absorption. The root accumulation of As was positively correlated with YG-14 root colonization. In addition, YG-14 promoted plant growth and alleviated oxidative damage in R. pseudoacacia L. under arsenic stress. This is the first study, from phenotype, physiology, and molecular perspectives, to determine the role of endophyte in promoting As phytostabilization and maintaining the growth of the host plant. This demonstrated the feasibility of using endophytes with high siderophore production to assist host plants in As phytoremediation.
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Arsénico , Contaminantes del Suelo , Arsénico/metabolismo , Enterobacter/metabolismo , Sideróforos/metabolismo , Endófitos , Plantas/metabolismo , Suelo , Biodegradación Ambiental , Contaminantes del Suelo/metabolismoRESUMEN
Ferroptosis is an iron-dependent cell death that was discovered recently. For beneficial microbes to establish mutualistic relationships with hosts, precisely controlled cell death in plant cells is necessary. However, whether ferroptosis is involved in the endophyteâplant system is poorly understood. Here, we reported that endophytic Streptomyces hygroscopicus OsiSh-2, which established a sophisticated and beneficial interaction with host rice plants, caused ferroptotic cell death in rice characterized by ferroptosis- and immune-related markers. Treatments with ferroptosis inhibitors and inducers, different doses of OsiSh-2, and the siderophore synthesis-deficient mutant ΔcchH revealed that only moderate ferroptosis induced by endophytes is essential for the establishment of an optimal symbiont to enhance plant growth. Additionally, ferroptosis involved in a defence-primed state in rice, which contributed to improved resistance against rice blast disease. Overall, our study provides new insights into the mechanisms of endophyteâplant interactions mediated by ferroptosis and suggests new directions for crop yield promotion.
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Resistencia a la Enfermedad , Endófitos , Ferroptosis , Oryza , Enfermedades de las Plantas , Streptomyces , Simbiosis , Oryza/microbiología , Oryza/genética , Oryza/inmunología , Ferroptosis/genética , Endófitos/fisiología , Resistencia a la Enfermedad/genética , Enfermedades de las Plantas/microbiología , Streptomyces/genética , Streptomyces/fisiología , Sideróforos/metabolismo , Hierro/metabolismoRESUMEN
A novel fully rigid, rod-shaped oligo(p-benzamide) (OPBA-6) molecule was designed and synthesized, which can be recrystallized into a three-dimensional (3D) multilayer material via an antiparallel molecular packing model. Intermolecular hydrogen bonding and π-π interaction are brought to ensure a strong intralayer interaction, while decoration of layer surface with sulfonic groups promotes water to enter interlayer space and facilitates the swelling and exfoliation of sample. With a simple dispersion in water, the obtained multilayer material can be easily swollen by water without destruction of in-plane morphology and subsequently delaminated into 2D nanosheets with thickness of about 5.38 nm. This achievement may be the first attempt to exfoliate layered organic materials and thus provide a new strategy to prepare 2D organic nanosheets without using any substrates or templates as required by conventional and widely used self-assembly routes. Based on exfoliated nanosheets, poly(vinyl alcohol) nanocomposites were prepared using a simple water solution processing method. A 64% increase in tensile stress and a 63% improvement in Young's modulus were achieved by addition of 7 wt % OPBA-6 loading.
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Benzamidas/química , Polímeros/química , Polímeros/síntesis química , Técnicas de Química Sintética , Modelos Moleculares , Conformación Molecular , Agua/químicaRESUMEN
Camellia oleifera (C. oleifera) is a unique edible oil crop in China cultivated in the hilly southern mountains. Although C. oleifera is classified as a drought-tolerant tree species, drought remains the main factor limiting the growth of C. oleifera in summer and autumn. Using endophytes to improve crop drought tolerance is one effective strategy to meet our growing food crop demand. In this study, we showed that endophyte Streptomyces albidoflavus OsiLf-2 could mitigate the negative impact of drought stress on C. oleifera, thus improving seed, oil, and fruit quality. Microbiome analysis revealed that OsiLf-2 treatment significantly affected the microbial community structure in the rhizosphere soil of C. oleifera, decreasing both the diversity and abundance of the soil microbe. Likewise, transcriptome and metabolome analyses found that OsiLf-2 protected plant cells from drought stress by reducing root cell water loss and synthesizing osmoregulatory substances, polysaccharides, and sugar alcohols in roots. Moreover, we observed that OsiLf-2 could induce the host to resist drought stress by increasing its peroxidase activity and synthesizing antioxidants such as cysteine. A multi-omics joint analysis of microbiomes, transcriptomes, and metabolomes revealed OsiLf-2 assists C. oleifera in resisting drought stress. This study provides theoretical and technical support for future research on endophytes application to enhance the drought resistance, yield, and quality of C. oleifera.
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Tuning 3D refractive indices of polymers is urgently needed for optical films, but it is quite challenging. Here, we proposed a simple constrained uniaxial stretch method that successfully tuned the 3D refractive indices in cellulose triacetate (TAC) films plasticized with triethyl citrate (TEC). Our results suggest that, under constrained uniaxial stretch, the main chains and side groups prefer to orientate in the stretch direction and the constrained direction, respectively. Such a unique chain arrangement differentiates the refractive indices in three directions of the film. The branched small molecule TEC is also crucial for tuning refractive indices, which promotes chain activity and enhances the chain orientation under stretching, leading to a considerable change in refractive indices before samples fracture. The polymer film we fabricated possesses a direction-dependent optical performance, where the refractive index in the film thickness direction is between that of the stretch direction and constrained direction. This work provides a fundamental understanding on the chain structure and optical performance of polymer films. The constrained uniaxial stretch method, in general, should also be applicable to tuning other 3D physical properties through tuning the direction-dependent orientation of polymers.
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The mechanical properties of polymer glass are determined by both intermolecular local packing structures and aligned intrachain configurations. These configurations involve multiple space scales, and the underlying mechanism is not well understood yet. By applying mechanical stimulation to cold-drawn polymer glasses, the present simulation work shows a one-to-one correspondence between arising retractive stress and the segment orientation parameter on the length scale of the intrachain connecting bond. Such retractive stress is a newly produced enthalpic stress when segment orientation on the length scale of bonds and particle mobility coexist. This reveals a potential mechanism of how the intrachain orientation on the length scale of bonds influences the mechanical behaviors of polymer glasses.
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A biaxial stretching device is designed and developed for the real-time structural measurements of polymer films. This device adopts a vertical layout to perform real-time x-ray scattering measurements. It has a maximum stretching ratio of 8 × 8 in two perpendicular directions. Its maximum experimental temperature and stretching rate are 250 °C and 100 mm/s, respectively. The control accuracies of the experimental temperature and stretching rate are ±1 °C and 0.01 mm, respectively. All the parameters related to film biaxial processing, such as stretching speed, stretching ratio, and temperature, can be independently set. The device feasibility is demonstrated via a real-time experiment in a synchrotron radiation beamline. Wide-angle x-ray diffraction, small-angle x-ray scattering, and stress-strain data can be simultaneously obtained during various stretching modes. The proposed device fills the gap between the synchrotron radiation x-ray scattering technique and the biaxial stretching processing of polymer films. This device will play an important role in improving the understanding of the physics behind biaxial polymer processing.
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Soft materials with mechanical adaptability have substantial potential for various applications in tissue engineering. Gaining a deep understanding of the structural evolution and adaptation dynamics of soft materials subjected to cyclic stretching gives insight into developing mechanically adaptive materials. Here, we investigate the effect of hierarchy structure on the mechanical adaptation of self-healing hydrogels under cyclic stretching training. A polyampholyte hydrogel, composed of hierarchical structures including ionic bonds, transient and permanent polymer networks, and bicontinuous hard/soft-phase networks, is adopted as a model. Conditions for effective training, mild overtraining, and fatal overtraining are demonstrated in soft materials. We further reveal that mesoscale hard/soft-phase networks dominate the long-term memory effect of training and play a crucial role in the asymmetric dynamics of compliance changes and the symmetric dynamics of hydrogel shape evolution. Our findings provide insights into the design of hierarchical structures for adaptive soft materials.