Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges.

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

Separator Effect on Zinc Electrodeposition Behavior and Its Implication for Zinc Battery Lifetime.

Uncontrolled zinc electrodeposition is an obstacle to long-cycling zinc batteries. Much has been researched on regulating zinc electrodeposition, but rarely are the studies performed in the presence of a separator, as in practical cells. Here, we show that the microstructure of separators determines the electrodeposition behavior of zinc. Porous separators direct zinc to deposit into their pores and leave "dead zinc" upon stripping. In contrast, a nonporous separator prevents zinc penetration. Such a difference between the two types of separators is distinguished only if caution is taken to preserve the attachment of the separator to the zinc-deposited substrate during the entire electrodeposition-morphological observation process. Failure to adopt such a practice could lead to misinformed conclusions. Our work reveals the mere use of porous separators as a universal yet overlooked challenge for metal anode-based rechargeable batteries. Countermeasures to prevent direct exposure of the metal growth front to a porous structure are suggested.

Viscoelasticity in associating oligomers and polymers: experimental test of the bond lifetime renormalization model.

Recent findings that the association bond lifetimes τα* in associating polymers diverge from their supramolecular network relaxation times τc challenge past theories. The bond lifetime renormalization proposed by Rubinstein and coworkers [Stukalin et al., Macromolecules, 2013, 46, 7525] provides a promising explanation. To examine systematically its applicability, we employ shear rheology and dielectric spectroscopy to study telechelic associating polymers with different main chain (polypropylene glycol and polydimethylsiloxane), molecular weight (below entanglement molecular weight) and end groups (amide, and carboxylic acid) which form dimeric associations by hydrogen bonding. The separation between τc (probed by rheology) and τα* (probed by dielectric spectroscopy) strongly increases with chain length as qualitatively predicted by the model. However, to describe the increase quantitatively, a transition from Rouse to reptation dynamics must be assumed. This suggests that dynamics of super-chains must be considered to properly describe the transient network.

Conspicuity of Malignant Liver Tumors on Diffusion-Weighted Imaging With Short tau Inversion Recovery After Gadolinium Ethoxybenzyl Diethylenetriaminepentaacetic Acid Administration.

BACKGROUND: Diffusion-weighted imaging (DWI) has been used for the detection and characterization of liver tumors because it has excellent contrast resolution. DWI using short tau inversion recovery (STIR) can improve tumor-to-liver contrast after gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration that shortens the T1 relaxation of liver parenchyma. PURPOSE: To quantitatively and qualitatively compare the conspicuity of malignant liver tumors on DWI after Gd-EOB-DTPA administration between STIR and chemical shift selective (CHESS) sequences. STUDY TYPE: Single-institution retrospective study. SUBJECTS: Fifty-seven patients with histologically confirmed malignant liver tumors were evaluated. FIELD STRENGTH/SEQUENCE: Low b-value DWIs with STIR and CHESS sequences 18-20 minutes after Gd-EOB-DTPA administration were acquired at 1.5T. ASSESSMENT: Tumor contrast-to-noise ratio (CNR) and visual grade of tumor conspicuity on DWI between STIR and CHESS sequences were compared. STATISTICAL TESTS: Paired Student's t-test and the Wilcoxon signed rank-test were applied. P < 0.05 was considered statistically significant. RESULTS: The mean tumor CNR and visual grade of tumor conspicuity on DWI were significantly higher for STIR than for CHESS (both P < 0.001). Regardless of the presence of chronic liver disease, the mean CNR (normal liver 33.5 ± 19.8 vs. 15.7 ± 12.2, P < 0.001; chronic liver disease 19.6 ± 11.0 vs. 9.2 ± 7.8, P < 0.001) and the visual conspicuity grade (normal liver 3.36 ± 0.64 vs. 2.56 ± 0.77, P < 0.001; chronic liver disease 2.94 ± 0.80 vs. 2.25 ± 0.84, P = 0.001) were significantly higher for STIR than for CHESS. Mean CNR and the visual conspicuity grade were also significantly higher for STIR than for CHESS in patients with hepatocellular carcinomas (CNR 18.1 ± 10.5 vs. 8.8 ± 7.2, P < 0.001; visual grade 2.88 ± 0.83 vs. 2.22 ± 0.87, P = 0.001) or metastases (CNR 35.0 ± 19.3 vs. 16.2 ± 13.1, P < 0.001; visual grade 3.45 ± 0.51 vs. 2.59 ± 0.73, P < 0.001). DATA CONCLUSION: DWI using STIR may be more helpful for depicting malignant liver tumors after Gd-EOB-DTPA administration compared with DWI using CHESS. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:565-573.

Materials for the Recovery of Uranium from Seawater.

More than 1000× uranium exists in the oceans than exists in terrestrial ores. With nuclear power generation expected to increase over the coming decades, access to this unconventional reserve is a matter of energy security. With origins in the mid-1950s, materials have been developed for the selective recovery of seawater uranium for more than six decades, with a renewed interest in particular since 2010. This review comprehensively surveys materials developed from 2000-2016 for recovery of seawater uranium, in particular including recent developments in inorganic materials; polymer adsorbents and related research pertaining to amidoxime; and nanostructured materials such as metal-organic frameworks, porous-organic polymers, and mesoporous carbons. Challenges of performing reliable and reproducible uranium adsorption studies are also discussed, as well as the standardization of parameters necessary to ensure valid comparisons between different adsorbents.

What dielectric spectroscopy can tell us about supramolecular networks⋆.

Polymers which can form supramolecular networks are a promising class of materials to provide highly sought-after properties such as self-healing, enhanced mechanical strength, super-stretchability as well as easy recyclability. However, due to the vast range of possible chemical structures it is very demanding to optimize these materials for the desired performance. Consequently, a detailed understanding of the molecular processes that govern the macroscopic properties is paramount to their technological application. Here we discuss some telechelic model systems with hydrogen-bonding end groups and how dielectric spectroscopy in combination with linear oscillatory shear rheology helped to understand the association mechanism on a molecular scale, and verify the model of bond-lifetime renormalization. Furthermore, we analyze a limitation of these H-bonding polymers, namely that there is a trade-off between high plateau modulus and long terminal relaxation time --both cannot be maximized at the same time. Finally, we show how more complex end groups phase separate from the main chain melt and thus lead to a more sophisticated rheological behavior which can overcome that limitation.

Structural correlations tailor conductive properties in polymerized ionic liquids.

Polymerized ionic liquids (PolyILs) are promising materials for applications in electrochemical devices spanning from fuel cells to capacitors and batteries. In principle, PolyILs have a competitive advantage over traditional electrolytes in being single ion conductors and thus enabling a transference number close to unity. Despite this perceived advantage, surprisingly low room temperature ionic conductivities measured in the lab raise an important fundamental question: how does the molecular structure mediate conductivity? In this work, wide-angle X-ray scattering (WAXS), vibrational sum frequency generation (vSFG), and density functional theory (DFT) calculations were used to study the bulk and interfacial structure of PolyILs, while broad band dielectric spectroscopy (BDS) was used to probe corresponding dynamics and conductive properties for a series of the PolyIL samples with tunable chemistries and structures. Our results reveal that the size of the mobile anions has a tremendous impact on chain packing in PolyILs that wasn't addressed previously. Larger mobile ions tend to create a well-packed structure, while smaller ions frustrate chain packing. The magnitude of these changes and level of structural heterogeneity are shown to depend on the chemical functionality and flexibility of studied PolyILs. Furthermore, these experimental and computational results provide new insight into the correlation between conductivity and structure in PolyILs, suggesting that structural heterogeneity helps to reduce the activation energy for ionic conductivity in the glassy state.

Hydrogen-bond strength changes network dynamics in associating telechelic PDMS.

Associating polymers are a class of materials with widely tunable macroscopic properties. Here, we investigate telechelic poly(dimethylsiloxanes) of several molecular weights (MW) with different hydrogen bonding end groups. Besides the well-established increase of the glass transition temperature Tg with decreasing MW, Tg remains unchanged as the end group varies from NH2 over OH to COOH. For the latter system, a 2nd Tg is found which indicates a segregated phase. In contrast, rheological measurements reveal a qualitative difference in the viscoelastic response of NH2-terminated and COOH-terminated chains. Both systems show clear signs of end group association, but only the latter exhibits an extended rubbery plateau. All features observed in the rheology experiments have corresponding processes in the dielectric measurements. This provides insight into the underlying molecular mechanisms, and especially reveals that many end groups of the COOH-terminated chains phase segregate while a certain fraction forms binary associates and remains non-segregated. In contrast, the NH2-terminated systems form only binary associates increasing the effective chain length, whereas the COOH-terminated system consists of two types of associates forming a crosslinked network. Remarkably, a single species of end group forms two qualitatively different types of associates: transient bonds which allow stress release by a bond-partner exchange mechanism, and effectively permanent bonds formed by a phase segregated fraction of end groups which are stable on the timescale of the transient mechanism.

Tunable synthetic control of soft polymeric nanoparticle morphology.

With a growing variety of nanoparticles available, research probing the influence of particle deformability, morphology, and topology on the behavior of all polymer nanocomposites is also increasing. In particular, the behavior of soft polymeric nanoparticles in polymer nanocomposites has displayed unique behavior, but their precise performance depends intimately on the internal structure and morphology of the nanoparticle. With the goal of providing guidelines to control the structure and morphology of soft polymeric nanoparticles, we have examined monomer starved semi-batch nano-emulsion polymerizations that form organic, soft nanoparticles, to correlate the precise structure of the nanoparticle to the rate of monomer addition and crosslinking density. The synthesis method produces 5-20 nm radii polystyrene nanoparticles with tunable morphologies. We report small angle neutron scattering (SANS) results that correlate synthetic conditions to the structural characteristics of soft polystyrene nanoparticles. These results show that the measured molecular weight of the nanoparticles is controlled by the monomer addition rate, the total nanoparticle radius is controlled by the excess surfactant concentration, and the crosslinking density has a direct effect on the topology of each nanoparticle. These studies thus provide pathways to control these 3 structural characteristics of the nanoparticle. This research, therefore provides a conduit to thoroughly investigate the effect of structural features of soft nanoparticles on their individual properties and those of their polymer nanocomposites.

A Rayleighian approach for modeling kinetics of ionic transport in polymeric media.

We report a theoretical approach for analyzing impedance of ionic liquids (ILs) and charged polymers such as polymerized ionic liquids (PolyILs) within linear response. The approach is based on the Rayleigh dissipation function formalism, which provides a computational framework for a systematic study of various factors, including polymer dynamics, in affecting the impedance. We present an analytical expression for the impedance within linear response by constructing a one-dimensional model for ionic transport in ILs/PolyILs. This expression is used to extract mutual diffusion constants, the length scale of mutual diffusion, and thicknesses of a low-dielectric layer on the electrodes from the broadband dielectric spectroscopy measurements done for an IL and three PolyILs. Also, static dielectric permittivities of the IL and the PolyILs are determined. The extracted mutual diffusion constants are compared with the self-diffusion constants of ions measured using pulse field gradient (PFG) fluorine nuclear magnetic resonance (NMR). For the first time, excellent agreement between the diffusivities extracted from the Electrode Polarization spectra (EPS) of IL/PolyILs and those measured using the PFG-NMR are found, which allows the use of the EPS and the PFG-NMR techniques in a complimentary manner for a general understanding of the ionic transport.

Unexpected Molecular Weight Effect in Polymer Nanocomposites.

The properties of the interfacial layer between the polymer matrix and nanoparticles largely determine the macroscopic properties of polymer nanocomposites (PNCs). Although the static thickness of the interfacial layer was found to increase with the molecular weight (MW), the influence of MW on segmental relaxation and the glass transition in this layer remains to be explored. In this Letter, we show an unexpected MW dependence of the interfacial properties in PNC with attractive polymer-nanoparticle interactions: the thickness of the interfacial layer with hindered segmental relaxation decreases as MW increases, in sharp contrast to theoretical predictions. Further analyses reveal a reduction in mass density of the interfacial layer with increasing MW, which can elucidate these unexpected dynamic effects. Our observations call for a significant revision of the current understandings of PNCs and suggest interesting ways to tailor their properties.

A case of gastric crystal-storing histiocytosis.

A 54-year-old male patient underwent upper gastrointestinal endoscopy, which revealed a 25-mm brown region in the angular section of the greater curvature of the stomach. The region was histologically determined to be gastric mucosa with an accumulation of histiocytes containing eosinophilic substances in the cytoplasm and chronic inflammatory cell infiltration. Histiocytes were immunohistologically positive for CD68, IgG, and κ. Based on these findings, the patient was diagnosed with gastric crystal-storing histiocytosis comprised of histiocytes phagocytosing IgG-κ-type immunoglobulin. This is a rare disease of which there have been no previous reports that included long-term follow-up. Here, we report the case with a literature review.

An impacted minor papilla stone in a patient with pancreas divisum that caused acute exacerbation of chronic pancreatitis: a case report.

A 75-year-old woman with epigastric pain was admitted to our emergency department. She was diagnosed with an acute exacerbation of chronic pancreatitis based on the results of blood tests and abdominal computed tomography (CT). The abdominal CT and magnetic resonance cholangiopancreatography revealed pancreas divisum. Abdominal CT also showed a stone in the minor papilla, with impaction of the stone being the most likely cause of the acute episode. Therefore, endoscopic sphincterotomy of the minor papilla and endoscopic naso-pancreatic duct drainage were performed to remove the stone and decrease the internal pressure of the pancreatic duct. These procedures improved the patient's clinical status. The naso-pancreatic drainage tube was removed, and her pancreatitis has not recurred. Herein, we report a rare case of an impacted minor papilla stone in a patient with pancreas divisum that caused an acute exacerbation of chronic pancreatitis.

Hemostasis by esophageal stent placement for management of esophageal tumor bleeding:a case report.

A 67-year-old male was diagnosed with advanced esophageal cancer. A computed tomography scan showed multiple intra-abdominal lymphadenopathies. Because the tumor was thought to be unresectable, we initiated chemotherapy. Twelve months later, the patient was admitted to our hospital because of hematemesis. Gastroduodenoscopy revealed oozing bleeding from the esophageal tumor. Hemostasis was not achieved with conservative treatment, and frequent blood transfusions were required. Endoscopic hemostasis was difficult to achieve because of the malignant esophageal stenosis. To treat the malignant esophageal stricture and esophageal tumor bleeding, we attempted to insert an esophageal covered self-expandable metallic stent. After the procedure, hemostasis was achieved by mechanical tamponade. Here we report a rare case of esophageal tumor bleeding that was managed with mechanical tamponade using an esophageal covered self-expandable metallic stent.

[Acute obstructive suppurative pancreatic ductitis after endoscopic retrograde cholangiopancreatography in a patient with carcinoma of the pancreatic head:a case report].

An 85-year-old woman with jaundice was referred to our hospital where she was diagnosed with obstructive jaundice due to carcinoma of the pancreatic head based on blood tests and abdominal computed tomography (CT). We performed endoscopic retrograde cholangiopancreatography (ERCP) for biliary drainage, but 5 days after the procedure, she complained of epigastric pain. Laboratory data revealed an elevated white blood cell count and a high serum amylase concentration. Follow-up CT 6 days after the ERCP revealed that the main pancreatic duct diameter had increased since the time of admission. Therefore, ERCP was performed for pancreatic ductal drainage. Purulent pancreatic juice was drained by endoscopic placement of a nasopancreatic drainage tube in the main pancreatic duct, resulting in marked alleviation of clinical symptoms;however, after removal of the tube, the abdominal pain recurred. Subsequent endoscopic placement of a pancreatic stent improved her clinical status once again. Herein, we report this rare case of acute obstructive suppurative pancreatic ductitis in a patient with carcinoma of the pancreatic head.

Ab Initio Screening of CO2-philic Groups.

Ab initio calculations were used to identify CO2-philic groups. Over 55 neutral molecules were screened for CO2 affinity via binding energetics. It is found that poly(ethylene oxide)s (PEO) oligomers with more than three repeating units are good CO2-binding groups, consistent with the high-performance of PEO-based materials for CO2/N2 separation. More interestingly, two triazole groups linked with a methylene chain are also excellent for CO2 binding with a favorable interaction of more than 28 kJ/mol, indicating that polymers or covalent-organic frameworks (COFs) with triazoles may be utilized for CO2 capture. This work provides a useful guide to introduce promising organic groups into polymeric membranes and COFs for CO2/N2 separation media.

[Rupture of a gastroduodenal artery aneurysm caused by duodenal ulcer: a case report].

A 73-year-old man with a history of tarry stools was admitted to our hospital. Gastroduodenoscopy on admission revealed an ulcer with an exposed vessel at the duodenal bulb. During endoscopic clipping for prevention of re-bleeding, a large amount of bleeding from the vessel was observed. Hemostasis was achieved after the procedure. However, 7 days later, the patient passed a large amount of tarry stools and experienced hypovolemic shock. Endoscopic re-examination revealed a pulsatile aneurysmal vessel at the base of the duodenal ulcer. Abdominal contrast-enhanced computed tomography and abdominal angiography demonstrated an aneurysm of the gastroduodenal artery, which was successfully treated with transcatheter arterial embolization. Thus, here we report a rare case of an aneurysm of the gastroduodenal artery caused by a duodenal ulcer.

[Gastric intramucosal cancer spreading to submucosal heterotopic gastric glands].

A 73-year-old man was referred to our hospital for further examination of an intra-abdominal mass. An upper gastrointestinal endoscopy revealed a 0-IIa+IIc lesion on the lesser curvature of the middle body. The lesion was diagnosed as early gastric cancer (tub1, SM), and a partial gastrectomy was performed. Pathological evaluation revealed a well-differentiated intramucosal adenocarcinoma that had partially spread to the submucosa. On immunohistochemical examination, the lesion displayed an intestinal phenotype. The submucosal lesion had poor stromal reaction, and there was smooth muscle tissue surrounding the lesion. As mentioned earlier, we diagnosed the lesion as a gastric intramucosal cancer spreading to the submucosal heterotopic gastric glands.