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Recently, many tough and self-healing hydrogels have been developed based on physical bonds as reversible sacrificial bonds. As breaking and re-forming of physical bonds are time-dependent, these hydrogels are viscoelastic and the deformation rate and temperature pronouncedly influence their fracture behavior. Using a polyampholyte hydrogel as a model system, we observed that the time-temperature superposition principle is obeyed not only for the small strain rheology but also for the large strain hysteresis energy dissipation and the fracture energy below a certain temperature. The three processes possess the same shift factors that obey the equation of Williams, Landel, and Ferry (WLF) time-temperature equivalence. The fracture energy Γ scales with the crack velocity Vc over a wide velocity range as Γ ~ Vc α (α = 0.21). The exponent α of the power law is well-related to the exponent κ of the relaxation modulus G (t) ~ t-κ (κ = 0.26), obeying the prediction α = κ/(1 + κ) from classic viscoelasticity theory. These results show that the fracture energy of the polyampholyte gel is dominated by the bulk viscoelastic energy dissipated around the crack tip. This investigation gives an insight into designing tough and self-healing hydrogels and predicting their fracture behaviors from their dynamic mechanical spectrum. [ABSTRACT FROM AUTHOR]

Polyampholyte (PA) hydrogels are a new class of tough and self-healing supramolecular hydrogels that have a potential as load-bearing soft materials. Studying on the creep behavior of these hydrogels and understanding the molecular mechanism are important for prediction of lifetime of the materials. In the present work, we study the creep rupture dynamics of the PA hydrogels with and without chemical cross-linking, in a certain observation time window. We have found that above some critical loading stress both physical and lightly chemically cross-linked hydrogels undergo creep rupture while moderately chemically cross-linked hydrogel resists creep flow. To elucidate the molecular mechanism, we have further compared the creep behaviors of the physical and lightly chemically cross-linked samples. The creep rate of the samples decreases with the creep time, following a power law relation, regardless of the loading stress variation. The fracture time of both of these hydrogels exponentially decreases with the increase of the loading stress, following the same master curve at high loading stress region, while the behavior of the two samples becomes different in the low loading stress region. We have explained the delayed fracture dynamics at high loading stress region in terms of a relatively weak strong bond rupture mechanism. [ABSTRACT FROM AUTHOR]

Recently, polyampolytes have been discovered to form hydrogels that possess high toughness, full resilience, and self-healing between two cut surfaces. The self-healing of this class of hydrogels is based on the re-forming of the multiple ionic bonds at the fractured surfaces, in which the mobility of the polymer segments and strength of the ionic bonds play an important role. In this work, we study the effects of healing temperature and chemistry of the polyampholyte hydrogels (chemical cross-linker density and chemical structure of the monomers) on the healing kinetics and healing efficiency. The high healing temperature substantially accelerates the self-healing kinetics. Chemical cross-linking reduces the self-healing efficiency. Monomers with more hydrophobic feature give a low self-healing efficiency. For polyampholyte physical hydrogels with a softening temperature below the room temperature, excellent healing efficiency (∼84% on average and maximum 99%) was observed without any external stimuli. We found a correlation between the self-healing efficiency and the fraction of dynamic bonds in the total bonds for relatively soft samples, which is an evidence that the self-healing is due to the re-forming of dynamic bonds. [ABSTRACT FROM AUTHOR]

Oppositely charged homopolyelectrolytes were found to form strong, tough, and self-healing polyion-complex (PIC) hydrogels, similar to polyampholytes (PA) which have opposite charges randomly distributed on the same polymer chains. The excellent mechanical performances of these two novel hydrogels are the results of dynamic ionic bonds formation between entangled polymer chains. For the PIC system, only interchain bonding occurs, while for the PA system both inter- and intrachain bonding exist. In addition, the ion pairs are expected to form stronger bonding in the PIC system than those in the PA system. In this work, we performed a comparative study of PIC hydrogels with the PA hydrogels. The PIC hydrogels are synthesized by sequential homopolymerization of cationic and anionic monomers at varied formulation, and their swelling and mechanical properties are systematically studied in comparison to the PA hydrogels that were synthesized from random copolymerization of anionic monomers and cationic monomers of the similar formulation. Different from the PA system which only forms tough hydrogels around zero net charge composition without chemical cross-linking, the PIC system forms tough physical hydrogels even at weakly off-balanced charge composition. At the charge-balanced composition, the low entanglement concentration of homocharged polyelectrolyte chains leads to tough PIC hydrogels formation at much lower concentrations than that of PA hydrogels. As a result, the PIC hydrogels are much tougher than the PA hydrogels prepared at the same monomer composition. In similar to PA hydrogels, the PIC hydrogels also exhibit broad dynamic mechanical spectra, indicating the formation of ion complexes with widely ranged bond strength. The PIC hydrogels have strong viscoelasticity in comparison with PA hydrogels. However, the two systems show the similar activation energies of the dynamic mechanical spectra. The SEM microstructural observation shows that the PIC hydrogels have segregated structure while PA hydrogels are more homogeneous. [ABSTRACT FROM AUTHOR]

Recently, we have reported that polyampholytes,synthesized fromfree radical copolymerization of anionic monomer and cationic monomer,form physical hydrogels of high toughness and self-healing. The randomdistribution of the opposite charges forms ionic bonds of a wide distributionof strength. The strong bonds serve as permanent cross-links, impartingelasticity, whereas the weak bonds serves as reversible sacrificialbonds by breaking and reforming to dissipate energy. In this work,we focus on the rupture behaviors of the polyampholyte physical hydrogel,P(NaSS-co-MPTC), copolymerized from sodium p-styrenesulfonate (NaSS) and 3-(methacryloylamino)propyltrimethylammoniumchloride (MPTC). Tensile test and pure shear test were performed atvarious stretch rates in the viscoelastic responses region of thematerial. Tensile test showed yielding, strain softening, and strainhardening, revealing the dually cross-linked feature of the gel. Pureshear test showed crack blunting at the notched tip and a large yieldingzone with butterfly shaped birefringence pattern ahead of the cracktip. After blunting, crack advanced at steady-state velocity witha constant angle. The conditions for the occurrence of crack bluntingand variables governing the crack advancing angle are discussed. Wefound that even for these highly stretchable samples, significantblunting only occurs when the tensile fracture stress σfis larger than modulus Eby a factor of about 2, in consistent with Hui’s theoreticalprediction for elastic materials. The crack advancing angle θwas found to be proportional to σy/Eover a wide stretch rate range, where σyis the yielding stress. In addition, thefracture energy was correlated to small strain modulus by a powerlaw in the viscoelastic response region. This systematic study willmerit revealing the fracture mechanism of tough viscoelastic materialsincluding biological tissues and recently developed tough and highlystretchable hydrogels. [ABSTRACT FROM AUTHOR]

On-surface polymerization represents a novel bottom-up approach for producing macromolecular structures. To date, however, most of the structures formed using this method exhibit a broad size distribution and are disorderly adsorbed on the surface. Here we demonstrate a strategy of using metal-directed template to control the on-surface polymerization process. We chose a bifunctional compound which contains pyridyl and bromine end groups as the precursor. Linear template afforded by pyridyl–Cu–pyridyl coordination effectively promoted Ullmann coupling of the monomers on a Au(111) surface. Taking advantage of efficient topochemical enhancement owing to the conformation flexibility of the Cu–pyridyl bonds, macromolecular porphyrin structures that exhibit a narrow size distribution were synthesized. We used scanning tunneling microscopy and kinetic Monte Carlo simulation to gain insights into the metal-directed polymerization at the single molecule level. The results reveal that the polymerization process profited from the rich chemistry of Cu which catalyzed the C–C bond formation, controlled the size of the macromolecular products, and organized the macromolecules in a highly ordered manner on the surface. [ABSTRACT FROM AUTHOR]

A series of poly(4-vinylpyridine)-b-poly(ε-caprolactone) (P4VP-PCL) diblock copolymers of different composition (namely, various nanostructured phases) were synthesized for hybridization with gold precursors. Interesting phase behavior of gold precursors/P4VP-PCL hybrids was found as evidenced by transmission electron microscopy and small-angle X-ray scattering (SAXS). Consistent with theoretical prediction, phase transformation in the hybrids with PCL-rich P4VP-PCL can be induced by the introduction of the gold precursors. In particular, the phase transformation can be achieved by introducing a very small amount of the gold precursors because of the significant increase in the effective excluded volume of hybridized P4VP microdomain as identified by SAXS experiments through the analysis of the 1D correlation function. This morphological evolution is referred to as the bridging mechanism, suggesting that the PCL block of the P4VP-PCL in the hybrids might play an important role in blocking the interconnection between hybridized P4VP microdomains. In contrast, disordered morphology was observed in the hybrids with P4VP-rich P4VP-PCL because of the strong association between the gold precursors and the P4VP block that might disrupt the ordered phase from microphase separation. [ABSTRACT FROM AUTHOR]

This study quantitatively measured neonicotinoids in various foods that are common to human consumption. All fruit and vegetable samples (except nectarine and tomato) and 90% of honey samples were detected positive for at least one neonicotinoid; 72% of fruits, 45% of vegetables, and 50% of honey samples contained at least two different neonicotinoids in one sample, with imidacloprid having the highest detection rate among all samples. All pollen samples from New Zealand contained multiple neonicotinoids, and five of seven pollens from Massachusetts detected positive for imidacloprid. These results show the prevalence of low-level neonicotinoid residues in fruits, vegetables, and honey that are readily available in the market for human consumption and in the environment where honeybees forage. In light of new reports of toxicological effects in mammals, the results strengthen the importance of assessing dietary neonicotinoid intakes and the potential human health effects.

Discusses the preparation and reduction of cyclophanes. Obtaining dienes in different rings; Hydrogenation of cyclophanes using Ramberg-Backlund reaction or a flash pyrolysis; Synthesis of cyclophanes; Factors affecting the sulfur dioxide extrusion.

In the context of precision medicine, multiomics data integration provides a comprehensive understanding of underlying biological processes and is critical for disease diagnosis and biomarker discovery. One commonly used integration method is early integration through concatenation of multiple dimensionally reduced omics matrices due to its simplicity and ease of implementation. However, this approach is seriously limited by information loss and lack of latent feature interaction. Herein, a novel multiomics early integration framework (MOINER) based on information enhancement and image representation learning is thus presented to address the challenges. MOINER employs the self-attention mechanism to capture the intrinsic correlations of omics-features, which make it significantly outperform the existing state-of-the-art methods for multiomics data integration. Moreover, visualizing the attention embedding and identifying potential biomarkers offer interpretable insights into the prediction results. All source codes and model for MOINER are freely available https://github.com/idrblab/MOINER.

The construction of p-n heterojunctions has become a widely adopted strategy for achieving the selective detection of reducing gases, including H 2 and CO. Nevertheless, the elucidation of the gas selectivity mechanism at the nanoscale remains elusive. First-principle calculations provide an attractive avenue for comprehending the influence of coordination structures on gas-sensitive selectivity, thereby unveiling the structure-activity relationship of p-n heterojunction sites. In this study, we investigate the selective adsorption behavior of H 2 and CO on a NiO-TiO 2 heterojunction using density functional theory. The results of d-band center analysis confirm that the NiO-TiO 2 heterojunction with adsorbed oxygen significantly enhances the adsorption stability of reducing gases. Intriguingly, our calculations reveal that H 2 has a higher affinity for adsorbed oxygen on the heterojunction surface compared to that of CO, corresponding to a lower H 2 adsorption energy. Density of states (DOS) results indicate that the NiO-TiO 2 heterojunction, with preadsorbed oxygen, exhibits ultrahigh selectivity with an n-type gas-sensitive response to H 2 , effectively eliminating the cross-sensitivity observed with CO, as confirmed by gas-sensitive characterization research. The sensing mechanism of the NiO-TiO 2 heterojunction's selective detection of H 2 without interference from CO can be visually explained by electron transfer and potential barrier changes, paving the way for future developments in novel, selective gas-sensitive materials.

Poor selectivity is a common problem faced by gas sensors. In particular, the contribution of each gas cannot be reasonably distributed when a binary mixture gas is co-adsorbed. In this paper, taking CO 2 and N 2 as an example, density functional theory is used to reveal the mechanism of selective adsorption of a transition metal (Fe, Co, Ni, and Cu)-decorated InN monolayer. The results show that Ni decoration can improve the conductivity of the InN monolayer while at the same time demonstrating an unexpected affinity for binding N 2 instead of CO 2 . Compared with the pristine InN monolayer, the adsorption energies of N 2 and CO 2 on the Ni-decorated InN are dramatically increased from -0.1 to -1.93 eV and from -0.2 to -0.66 eV, respectively. Interestingly, for the first time, the density of states demonstrates that the Ni-decorated InN monolayer achieves a single electrical response to N 2 , eliminating the interference of CO 2 . Furthermore, the d-band center theory explains the advantage of Ni decorated in gas adsorption over Fe, Co, and Cu atoms. We also highlight the necessity of thermodynamic calculations in evaluating practical applications. Our theoretical results provide new insights and opportunities for exploring N 2 -sensitive materials with high selectivity.