Thin supported silica membranes

This thesis discusses several transport-related aspects relevant for the application of thin supported silica membranes for gas separation and nanofiltration.\ud The influence of support geometry on overall membrane performance is investigated. Planar (i.e., flat plate), tubular, and multichannel support geometries are investigated in numerical simulations of the membrane performance in gas separation. The emphasis is laid on the last two membrane geometries which are considered more suitable due to their greater surface-area-to-volume ratio and mechanical robustness. The dusty-gas-model (DGM) is used, and the contribution of different transport mechanisms occurring in a porous system (Knudsen diffusion, bulk diffusion and viscous flow) is accounted for. The comparison of geometries is performed in terms of the calculated flux and selectivity, in case of separation of pure H2 and of a 50-50% binary H2/CH4 mixture. The multichannel configuration is found to be far less efficient than the multitubular one due to the inefficiency of the inner channels, even in the case of highly permeable silica - where the transport is governed by the support – and even though the surface-area-to-volume ratio is higher in the multichannel configuration. For a proper prediction of transport behaviour it is crucial to account for the three transport mechanisms included in the DGM, especially in case of the binary mixtures. Calculations for the binary mixture show that the inner channels contribute to a considerable decline of the selectivity. Even values below unity may be obtained in the case of highly permeable silica, i.e. indicating a higher transport rate of CH4 compared to H2. For a leaking inner channel, a maximum in selectivity is observed for a certain value of permeability of silica for H2. Further improvement of the silica membrane layer would thus result in a decreased performance of the multichannel membrane. \ud The transport of binary mixtures containing an inert mobile component such as He and a condensable component such as H2O through a microporous silica membrane has been investigated using spectroscopic ellipsometry. Attention is focussed to the correlation between the flux of the more mobile component and the sorption properties of the condensable component. A linear decline of the normalized He permeance as a function of water occupancy is observed. This behaviour is agreement with a theoretical description of the transport where the microporous medium is considered as an ideal lattice of sites. However, departures from linear behaviour are observed experimentally at low temperatures, where water has low molecular mobility, which can not be accounted for by the theoretical description.\ud It is demonstrated that an improved membrane performance in gas separation can be achieved by incorporating an additional intermediate surfactant templated silica layer between the supporting mesoporous -Al2O3 and the amorphous microporous silica top layer. The dual-layered silica membrane shows improved values of H2 flux and H2/CH4 permselectivity compared with that of a standard silica membrane.\ud Throughout this thesis spectroscopic ellipsometry is used as a non-destructive characterization technique to determine the thickness and porosity of the asdeposited membrane layers, but also to monitor in-situ the sorption of water by the membrane.\ud Improved ion retention can be achieved by using a bilayered nanofiltration membrane. The novel bilayered membrane concept is based on a difference in iso-electric point between the two separating layers in the membrane allowing improved ion retention over a large pH range. The composite membrane consisting of a -alumina layer and a surfactant templated silica layer, similar to that investigated for the improvement of membrane performance in gas separation, is analyzed in terms of the retention of monovalent ions (Na+, Cl-) over the pH range 4-10. A good agreement is found between experimental data and model predictions, with a discrepancy at high pH (pH 10) in case of sodium retention

Normotensive rats with PCOS exhibit the hypertensive pattern: focus on oxidative stress

Numerous evidence implies complex interrelations between polycystic ovary syndrome (PCOS) and hypertension (HT) in reproductive-age women. In this study, we aimed to investigate the potential strain differences in ovarian morphology, hemodynamic, and biochemical characteristics in an androgen-induced PCOS rat model. A total of 24 rats of 3 weeks old (12 Wistar Kyoto - WK and 12 spontaneously hypertensive rats - SHR) were divided into four groups: WK, WK PCOS, SHR, and SHR PCOS. PCOS was induced by daily s.c. injections of testosterone enanthate (1 mg/100 g body weight) administered for 5 weeks. PCOS induction led to estrus cyclicity cessation, cystic ovarian appearance, and sex hormones disturbances in both strains. The morphometric parameters in ovaries were altered in a manner of PCOS-related changes in both strains (higher number in preantral, atretic, and cystic follicles). Ultrasonographically, a significant decrease in ovarian volume (OV) was registered in PCOS groups but also in SHR compared to WK rats. All blood pressure parameters were higher in SHR compared to WK. PCOS modeling increased systolic, mean arterial, and pulse pressure in WK strain, while in SHR, only mean arterial and pulse pressure were higher. Alterations in oxidative stress parameters could provide a molecular basis for PCOS-related changes: in PCOS groups, thiobarbituric acid reactive substance and superoxide anion radical levels were higher in both strains, while superoxide dismutase and glutathione were significantly lowered

Interleukin-6 receptor specific RNA aptamers for cargo delivery into target cells

Aptamers represent an emerging strategy to deliver cargo molecules, including dyes, drugs, proteins or even genes, into specific target cells. Upon binding to specific cell surface receptors aptamers can be internalized, for example by macropinocytosis or receptor mediated endocytosis. Here we report the in vitro selection and characterization of RNA aptamers with high affinity (Kd = 20 nM) and specificity for the human IL-6 receptor (IL-6R). Importantly, these aptamers trigger uptake without compromising the interaction of IL-6R with its natural ligands the cytokine IL-6 and glycoprotein 130 (gp130). We further optimized the aptamers to obtain a shortened, only 19-nt RNA oligonucleotide retaining all necessary characteristics for high affinity and selective recognition of IL-6R on cell surfaces. Upon incubation with IL-6R presenting cells this aptamer was rapidly internalized. Importantly, we could use our aptamer, to deliver bulky cargos, exemplified by fluorescently labeled streptavidin, into IL-6R presenting cells, thereby setting the stage for an aptamer-mediated escort of drug molecules to diseased cell populations or tissues

Minimal information for studies of extracellular vesicles 2018 (MISEV2018):a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (“MISEV”) guidelines for the field in 2014. We now update these “MISEV2014” guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points

Parenting Styles as Predictors of Adolescents’ Self-Efficacy and Subjective Well-Being

The aim of the research was to determine the predictive power of parenting styles in predicting subjective well-being and self-efficacy as aspects of adolescent mental health. The sample consisted of 270 students from four high schools in Serbia, aged 16 and 17. The research was conducted during March and April 2021, and research methods that were used are descriptive statistics, correlation analysis and regression analysis. The authoritative parental educational style contributes to the development of adolescents’ experience of self-efficacy and subjective well-being. Authoritative parents - through high warmth and control - provide the child with an optimal environment for development

Gas transport efficiency of ceramic membranes: comparison of different geometries

The effect of support geometry on the performance of asymmetric ceramic membranes for gas separation is analyzed. Flat plate (FP), tubular (TU) and multichannel (MC) geometries are investigated using the dusty gas model (DGM) to describe transport of a multicomponent gas mixture through the macroporous support. It is shown that: (a) the support geometry significantly affects membrane performance; (b) in the case of the multichannel geometry, the inner channels do not contribute efficiently to the overall gas transport; (c) best performance in terms of both flux and permselectivity is obtained for tubular geometry. It is furthermore clarified that for an accurate description of the transport behaviour it is crucial to properly account for the relative contributions of all different transport mechanisms (Knudsen diffusion, bulk diffusion and viscous flow) included in the DGM

Characterization and transport properties of surfactant-templated silica layers for membrane applications

An intermediate surfactant-templated silica (STS) layer is applied between the supporting mesoporous gamma-Al2O3 and the amorphous microporous silica overlayer resulting in dual-layered microporous silica membranes for gas separation applications that show improved values for both hydrogen flux and selectivity. Determination of thickness and porosity of as-deposited membrane layers by spectroscopic ellipsometry reveals that the STS layer is present as a distinctive layer of sim20 nm thickness, with penetration up to a depth of sim70 nm into the underlying gamma-Al2O3support layer, whose thickness and porosity are determined to be 1.3 mgrm and 50%, respectively

The Effect of Nanofibrillated Tempo-oxidized Cotton Linters on the Strength and Optical Properties of Paper

This study elaborates the application of composite films based on nanofibrillated cellulose obtained from cotton linters oxidized in the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system, with the use of CaCO3 and/or Al(OH)(3) as fillers, and glycols as plasticizers, to improve the mechanical, optical, and sorption properties of paper. The paper coating with nanofibrillated cellulose-based films, without additional adhesive, depending on the concentration of nanofibrillated cellulose in the dispersion and the type of filler, improves the mechanical properties of paper, and decreases sorption properties, while no significant changes were observed in optical properties compared to the initial papers

Electrolyte retention of supported bi-layered nanofiltration membranes

The electrolyte separation behaviour of a supported bi-layered ceramic membrane is investigated experimentally and the measured ion retentions\ud are compared with the predictions of a site-binding transport model with no adjustable parameters. Due to the difference in iso-electric point\ud between its two separating layers, the bi-layered system is expected to perform better over a large pH range compared with a membrane with only\ud one type of selective layer. The separating layers in the membrane are a microporous silica and a mesoporous -alumina (pore sizes of 0.8 and\ud 2 nm, respectively) and their retention is studied for a binary electrolyte solution of NaCl at 1 mol/m3 for pH values between 4 and 10.\ud Because of its smaller pores and high charge, the silica layer mainly determines the membrane retention at neutral and alkaline pH, while the\ud -alumina layer has a significant impact on the NaCl retention at 4 < pH< 5. The model predictions are in good agreement with the experimental\ud data for Na+ at 4 < pH< 9 and for Cl− at the whole pH range. For a pH of 4, the predicted chloride retention is lower than the sodium retention\ud while the experimental data show the opposite effect.\ud © 2005 Elsevier B.V. All rights reserved