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Polymer electrolyte membranes with bicontinuous microphases comprising soft hydrated domains and mechanically robust hydrophobic domains are used in a wide range of electrochemical devices including fuel cells and electrolyzers. The self-assembly, water uptake, and proton conductivity of model block copolymer electrolytes with semicrystalline hydrophobic blocks were investigated. A series of sulfonated polystyrene-block-polyethylene (PSS-PE) copolymers were synthesized to probe the interplay between crystallization, morphology, hydration, and proton transport. In block copolymer systems with amorphous hydrophobic blocks, it has been shown that higher water update and proton conductivity are obtained in low molecular weight systems. However, crystallization is known to disrupt the self-assembly of low molecular weight block copolymers. We found that this disruption results in lower water uptake and proton conductivity. Increasing molecular weight results in less morphological disruption and improvement in performance. © 2014 American Chemical Society.

Background: Management of total anomalous pulmonary venous connections has been extensively studied to further improve outcomes. Our institution previously reported factors associated with mortality, recurrent obstruction, and reintervention. The study purpose was to revisit the cohort of patients and evaluate factors associated with reintervention, and mortality in early and late follow-up., Methods: A retrospective review at our institution identified 81 patients undergoing total anomalous pulmonary venous connection repair from January 2002 to January 2018. Demographic and operative variables were evaluated. Anastomotic reintervention (interventional or surgical) and/or mortality were primary endpoints., Results: Eighty-one patients met the study criteria. Follow-up ranged from 0 to 6,291 days (17.2 years), a mean of 1263 days (3.5 years). Surgical mortality was 16.1% and reintervention rates were 19.8%. In re-interventions performed, 80% occurred within 1.2 years, while 94% of mortalities were within 4.1 months. Increasing cardiopulmonary bypass times (p = 0.0001) and the presence of obstruction at the time of surgery (p = 0.025) were predictors of mortality, while intracardiac total anomalous pulmonary venous connection type (p = 0.033) was protective. Risk of reintervention was higher with increasing cardiopulmonary bypass times (p = 0.015), single ventricle anatomy (p = 0.02), and a post-repair gradient >2 mmHg on transesophageal echocardiogram (p = 0.009)., Conclusions: Evaluation of a larger cohort with longer follow-up demonstrated the relationship of anatomic complexity and symptoms at presentation to increased mortality risk after total anomalous pulmonary venous connection repair. The presence of a single ventricle or a post-operative confluence gradient >2 mmHg were risk factors for reintervention. These findings support those found in our initial study.

Background: Neonates undergoing congenital heart defect repair require optimized nutritional support in the perioperative period. Utilization of a gastrostomy tube is not infrequent, yet optimal timing for placement is ill-defined. The objective of this study was to identify characteristics of patients whose postoperative course included gastrostomy tube placement to facilitate supplemental tube feeding following neonatal repair of congenital heart defects., Methods: A single-institution, retrospective chart review identified 64 consecutive neonates who underwent cardiac operations from 2012 to 2016. Perioperative variables were evaluated for significance in relation to gastrostomy tube placement., Results: A total of 27 (42%) underwent gastrostomy tube placement. Diagnosis of a genetic syndrome was associated with the likelihood of placement of gastrostomy tube ( P = .032), as were patients with single ventricle physiology ( P = .0013) compared to those felt to be amenable to eventual biventricular repair. Aortic arch reconstruction ( P = .029), as well as the need for delayed sternal closure ( P = .05), was associated with increased frequency of gastrostomy tube placement. Postoperative outcomes including the number of days intubated ( P = .0026) and the presence of significant dysphagia ( P = .0034) were associated with gastrostomy placement. Additionally, genetic syndrome ( P = .003), aortic arch reconstruction ( P = .01), and postoperative intubation duration ( P = .0024) correlated with increased length of stay, where increased length of stay was associated with gastrostomy tube placement ( P = .0004)., Discussion: Patient characteristics that were associated with a high likelihood of eventual gastrostomy placement were identified in this study. Early recognition of such characteristics in future patients may allow for reduced time to gastrostomy tube placement, which in turn may improve perioperative growth and outcomes.

Reparative procedures are not always feasible in congenitally abnormal mitral valves. Mechanical prosthesis has been accepted as the choice for valve replacement in the pediatric population. This report describes a case of congenital mitral valve disease requiring mitral valve replacement. The infant's mitral valve annulus was not amenable to placement of the smallest available mechanical prosthesis. The approach used here for annular and subvalvular enlargement facilitated implantation of a larger prosthesis for congenital mitral valve replacement. Five-year outcomes in a single patient may indicate broader applicability and avoidance of patient-prosthesis mismatch., (Copyright © 2016 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Hydrated membranes with cocontinuous hydrophilic and hydrophobic phases are needed to transport protons in hydrogen fuel cells. Herein we study the water uptake and proton conductivity of a model fuel cell membrane comprising a triblock copolymer, polystyrenesulfonate-block-polyethylene-block-polystyrenesulfonate (S-SES), as a function of water activity in both humid air and liquid water. We demonstrate that the water uptake and proton conductivity of S-SES membranes equilibrated in liquid water are fundamentally different from values obtained when they were equilibrated in humid air. The morphological underpinnings of our observations were determined by synchrotron small-angle X-ray scattering and cryogenic scanning transmission electron microscopy. A discontinuous increase in conductivity when nearly saturated humid air is replaced with liquid water coincides with the emergence of heterogeneity in the hydrated channels: a water-rich layer is sandwiched between two polymer-rich brushes. While the possibility of obtaining heterogeneous hydrated channels in polymer electrolyte membranes has been discussed extensively, to our knowledge, this is the first time that direct evidence for the formation of water-rich subdomains is presented.

This is a study of morphology, water uptake, and proton conductivity of a sulfonated polystyrene-block-polyethylene (PSS-PE) copolymer equilibrated in humid air with controlled relative humidity (RH), and in liquid water. Extrapolation of the domain size, water uptake, and conductivity obtained in humid air to RH = 100% allowed for an accurate comparison between the properties of PSS-PE hydrated in saturated vapor and in liquid water. We demonstrate that extrapolations of domain size and water uptake on samples equilibrated in humid air are consistent with measurements on samples equilibrated in liquid water. Small (5%) differences in proton conductivity were found in samples equilibrated in humid air and liquid water. We argue that differences in transport coefficients in disordered heterogeneous systems, particularly small differences, present no paradox whatsoever. Schroeder's Paradox, wherein properties of polymers measured in saturated water vapor are different from those obtained in liquid water, is thus not observed in the PSS-PE sample.

We report on the design and operation of a novel sample stage, used to simultaneously measure X-ray scattering profiles and conductivity of a polymer electrolyte membrane (PEM) surrounded by humid air as a function of temperature and relative humidity. We present data obtained at the Advanced Light Source and Stanford Synchrotron Radiation Laboratory. We demonstrate precise humidity control and accurate determination of morphology and conductivity over a wide range of temperatures. The sample stage is used to study structure-property relationships of a semi-crystalline block copolymer PEM, sulfonated polystyrene-block-polyethylene.

Nanoscale ionic aggregates are ubiquitous in copolymers containing charged and uncharged monomers. In most cases, these clusters persist when these polymers are hydrated and ion-conducting channels percolate through the sample. We argue that these clusters impede ion motion due to (1) the requirement that ions must hop across ion-free regions in the channels as they are transported from one cluster to the next, and (2) increased counterion condensation due to proximity of fixed acid groups in the clusters. Block copolymers wherein the size of the ion-containing microphase is 6 nm or less provides one approach for eliminating the clusters.

We report on the synthesis and morphology of a block copolymer, poly(3-(2'-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory-Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the "breaking out" of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization).