Investigation of the yielding transition in concentrated colloidal systems via rheo-XPCS.

We probe the microstructural yielding dynamics of a concentrated colloidal system by performing creep/recovery tests with simultaneous collection of coherent scattering data via X-ray Photon Correlation Spectroscopy (XPCS). This combination of rheology and scattering allows for time-resolved observations of the microstructural dynamics as yielding occurs, which can be linked back to the applied rheological deformation to form structure-property relations. Under sufficiently small applied creep stresses, examination of the correlation in the flow direction reveals that the scattering response recorrelates with its predeformed state, indicating nearly complete microstructural recovery, and the dynamics of the system under these conditions slows considerably. Conversely, larger creep stresses increase the speed of the dynamics under both applied creep and recovery. The data show a strong connection between the microstructural dynamics and the acquisition of unrecoverable strain. By comparing this relationship to that predicted from homogeneous, affine shearing, we find that the yielding transition in concentrated colloidal systems is highly heterogeneous on the microstructural level.

Structural change and dynamics of colloidal gels under oscillatory shear flow.

The dynamics and rheological behavior of colloidal gels under oscillatory shear flow have been studied by using the Brownian dynamics simulations. The dynamics is studied under the oscillatory shear of small, medium, and large amplitudes. In the small amplitude oscillatory shear (SAOS) regime, the colloidal gel retains a rigid-chain network structure. The colloidal gel oscillates with small structural fluctuations and the elastic stress shows a linear viscoelastic response. In the medium amplitude oscillatory shear (MAOS) regime, the rigid network structure is ruptured, and a negative correlation between the absolute value of strain and the average bond number is observed. The elastic stress shows a transient behavior in between the SAOS and LAOS responses. In the large amplitude oscillatory shear (LAOS) regime, the colloidal gel shows a soft chain structure. Contrary to the negative correlation in the MAOS regime, the colloidal gel shows an oscillating dynamics with a positive correlation between the absolute value of strain and the average bond number. The soft chain structure exhibits no elasticity at small strain, while it shows strong elasticity at large strain. The oscillating dynamics and the rheological behavior are discussed in terms of the microstructural change from the rigid to soft chain structure.

Probing metal-carboxylate interactions in cellulose nanofibrils-based hydrogels using nonlinear oscillatory rheology.

Cellulose nanofibrils (CNFs) have gained much attention as part of biocompatible soft hydrogels used in various biomedical applications such as biodegradable scaffolds, biomedicine, tissues, and regenerative medicine. The CNF hydrogels were mediated with metal cations for improved mechanical strength and structural reversibility. Intermolecular interactions in these CNF hydrogels are controlled by metal cation-carboxylate coordination bonding, leading to the creation of interconnected three-dimensional nanofibril structures that produce high structural reversibility. The nonlinear inter- and intra-cycle were investigated viscoelastic responses of these CNF hydrogels by quantitative nonlinear viscoelastic parameters and transient responses. The dynamic and transitional analyses conducted indicate that the structural deformation and recovery characteristics of the CNF hydrogels are affected by the valency number of the metal cations. This property can be carefully chosen to tune the intermolecular interactions between the cellulose nanofibrils to create an efficient interwoven network structure with high structural reversibility that can go through repeated cycles of reformation and yielding.

Enhanced Double Metal Cyanide Catalysts for Modulating the Rheological Properties of Poly(propylene carbonate) Polyols by Modifying Carbonate Contents.

Poly(propylene carbonate) (PPC) polyol is an environmentally sustainable material derived from abundant and renewable greenhouse gas, CO2. Optimizing their synthesis and properties is crucial to their application in the production of polyurethane products. In this study, we synthesized PPC polyols with varying carbonate contents using heterogeneous Zn/Co double metal cyanide (DMC) catalysts, which were prepared with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as an effective complexing agent. Analysis of the influence of calcination temperature revealed that the DMC-P123 catalyst calcined at 100 °C exhibited superior catalytic performance owing to reduced crystallinity and enhanced formation of the monoclinic phase. Additionally, by precisely controlling the CO2 pressure, high propylene carbonate contents of up to 32.8 wt % in the polyol structure were achieved. The increased carbonate content enhanced the intermolecular attraction between polyol chains, thereby promoting hydrogen bonding and significantly modulating the rheological properties of the polyol. The novel findings of this study establish a solid foundation for the synthesis of CO2-based polyols with desirable properties, serving as alternatives to conventional petroleum-based polyols.

Role of Adsorbed Polymers on Nanoparticle Dispersion in Drying Polymer Nanocomposite Films.

Polymers adsorbed on nanoparticles (NPs) are important elements that determine the dispersion of NPs in polymer nanocomposite (PNC) films. While previous studies have shown that increasing the number of adsorbed polymers on NPs can improve their dispersion during the drying process, the exact mechanism remained unclear. In this study, we investigated the role of adsorbed polymers in determining the microstructure and dispersion of NPs during the drying process. Investigation of the structural development of NPs using the synchrotron vertical-small-angle X-ray scattering technique revealed that increasing polymer adsorption suppresses bonding between the NPs at later stages of drying, when they approach each other and come in contact. On the particle length scale, NPs with large amounts of adsorbed polymers form loose clusters, whereas those with smaller amounts of adsorbed polymers form dense clusters. On the cluster length scale, loose clusters of NPs with large amounts of adsorbed polymers build densely packed aggregates, while dense clusters of NPs with small amounts of adsorbed polymers become organized into loose aggregates. The potential for the quantitative control of NP dispersion in PNC films via modification of polymer adsorption was established in this study.

Role of PVDF in Rheology and Microstructure of NCM Cathode Slurries for Lithium-Ion Battery.

A binder plays a critical role in dispersion of coating liquids and the quality of coating. Poly(vinylidene fluoride) (PVDF) is widely used as a binder in cathode slurries; however, its role as a binder is still under debate. In this paper, we study the role of PVDF on the rheology of cathode battery slurries consisting of Li(Ni1/3Mn1/3Co1/3)O2 (NCM), carbon black (CB) and N-methyl-2-pyrrolidone (NMP). Rheology and microstructure of cathode slurries are systemically investigated with three model suspensions: CB/PVDF/NMP, NCM/PVDF/NMP and NCM/CB/PVDF/NMP. To highlight the role of PVDF in cathode slurries, we prepare the same model suspensions by replacing PVDF with PVP, and we compare the role of PVDF to PVP in the suspension rheology. We find that PVDF adsorbs neither onto NCM nor CB surface, which can be attributed to its poor affinity to NCM and CB. Rheological measurements suggest that PVDF mainly increases matrix viscosity in the suspension without affecting the microstructure formed by CB and NCM particles. In contrast to PVDF, PVP stabilizes the structure of CB and NCM in the model suspensions, as it is adsorbed on the CB surface. This study will provide a useful insight to fundamentally understand the rheology of cathode slurries.

Studying Large Amplitude Oscillatory Shear Response of Soft Materials.

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl sulfoxide (DMSO) and xanthan gum in water - two concentrated polymer solutions used as viscosifiers in foods, enhanced oil recovery, and soil remediation. Understanding the nonlinear rheological behavior of soft materials is important in the design and controlled manufacturing of many consumer products. It is shown how the response to LAOS of these polymer solutions can be interpreted in terms of a clear transition from linear viscoelasticity to viscoplastic deformation and back again during a period. The LAOS results are analyzed via the fully quantitative Sequence of Physical Processes (SPP) technique, using free MATLAB-based software. A detailed protocol of performing a LAOS measurement with a commercial rheometer, analyzing nonlinear stress responses with the freeware, and interpreting physical processes under LAOS is presented. It is further shown that, within the SPP framework, a LAOS response contains information regarding the linear viscoelasticity, the transient flow curves, and the critical strain responsible for the onset of nonlinearity.

Diatom Microbubbler for Active Biofilm Removal in Confined Spaces.

Bacterial biofilms form on and within many living tissues, medical devices, and engineered materials, threatening human health and sustainability. Removing biofilms remains a grand challenge despite tremendous efforts made so far, particularly when they are formed in confined spaces. One primary cause is the limited transport of antibacterial agents into extracellular polymeric substances (EPS) of the biofilm. In this study, we hypothesized that a microparticle engineered to be self-locomotive with microbubbles would clean a structure fouled by biofilm by fracturing the EPS and subsequently improving transports of the antiseptic reagent. We examined this hypothesis by doping a hollow cylinder-shaped diatom biosilica with manganese oxide (MnO2) nanosheets. In an antiseptic H2O2 solution, the diatoms doped by MnO2 nanosheets, denoted as diatom bubbler, discharged oxygen gas bubbles continuously and became self-motile. Subsequently, the diatoms infiltrated the bacterial biofilm formed on either flat or microgrooved silicon substrates and continued to generate microbubbles. The resulting microbubbles merged and converted surface energy to mechanical energy high enough to fracture the matrix of biofilm. Consequently, H2O2 molecules diffused into the biofilm and killed most bacterial cells. Overall, this study provides a unique and powerful tool that can significantly impact current efforts to clean a wide array of biofouled products and devices.

A pediatric case of relapsed pulmonary alveolar proteinosis despite successful whole lung lavage.

Pulmonary alveolar proteinosis (PAP) is a rare disease in children characterized by intra-alveolar accumulation of surfactant proteins, which severely reduces gaseous exchange. Whole lung lavage (WLL) is the preferred technique for the treatment of severe PAP. Herein, we present a pediatric case of PAP treated with WLL. An 11-year-old boy was admitted with the chief complaint of a dry cough lasting 6 months. He developed symptoms of dyspnea on exertion and had difficulty in climbing stairs. He was ultimately diagnosed with PAP through video-assisted thoracoscopic lung biopsy. As first-line of treatment for PAP, he underwent therapeutic WLL for each of his lungs on separate days. After a brief recovery, his symptoms gradually worsened; therefore, he underwent a second WLL. This is the first pediatric case of PAP relapse despite successful WLL in Korea.

Development and Validity Testing of the Worksite Health Index: An Assessment Tool to Help and Improve Korean Employees' Health-Related Outcome.

OBJECTIVES: The objective of this study was to develop the Worksite Health Index (WHI) and validate its psychometric properties. METHODS: The development of the WHI questionnaire included item generation, item construction, and field testing. To assess the instrument's reliability and validity, we recruited 30 different Korean worksites. RESULTS: We developed the WHI questionnaire of 136 items categorized into five domains, namely Governance and Infrastructure, Need Assessment and Planning, Health Prevention and Promotion Program, Occupational Safety, and Monitoring and Feedback. All WHI domains demonstrated a high reliability with good internal consistency. The total WHI scores differentiated worksite groups effectively according to firm size. Each domain was associated significantly with employees' health status, absence, and financial outcome. CONCLUSIONS: The WHI can assess comprehensive worksite health programs. This tool is publicly available for addressing the growing need for worksite health programs.

Mutations in ND subunits of complex I are an important genetic cause of childhood mitochondrial encephalopathies.

An increasing number of reports on mitochondrial DNA coding regions' mutations, especially in mitochondrial DNA- encoded NADH dehydrogenase (ND) subunit genes of the respiratory chain complex I, have been published recently, making it possible to improve the molecular diagnosis of many mitochondrial diseases in children with variable clinical features. This article describes 2 mitochondrial DNA mutations in the ND3 and ND5 genes in patients showing clinical features of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS)/Leigh syndrome overlap syndrome and atypical Leigh syndrome. These cases add to the increasing number of reports stating that mitochondrial DNA-encoded protein-coding regions are mutation hot spots in pediatric patients with encephalopathies with variable clinical spectra.