Formation Of Finger-like Structures Research Articles

Facile purification of palygorskite and its effect on the performance of reverse osmosis thin film nanocomposite membrane

AbstractBACKGROUNDPalygorskite (PAL) is a naturally occurring nanoclay characterized by a distinctive tubular structure and fibrous morphology, exhibiting chemical and thermal stability as well as large specific surface area. The tubular structure of PAL promotes the selective transportation of water molecules, hence can serve as an interesting candidate for liquid separation. In this work, a membrane substrate was fabricated using the purified PAL to enhance the flux of the thin film composite reverse osmosis. Purification of PAL enhances its interaction with polymer chain to further promote nanofiller dispersion and improves the hydrophilic properties. The water flux as well as salt rejection of the developed membranes was examined using a dead end filtration system. The membrane performance with respect to pure water flux and salt rejection was evaluated using reverse osmosis water and 2000 ppm sodium chloride solution at 15 bar operation pressure.RESULTSThe physico‐chemical characterization evidenced the role of purified PAL (P‐PAL) in increasing the number of pores and promoting the formation of finger like structure in the substrate layer. The water flux of thin film nanocomposite (TFN) containing P‐PAL exhibited 114.6% and 43.1% improvement compared to that of neat and TFN membrane incorporated with pristine PAL respectively without compromising the salt rejection performance.CONCLUSIONSThis study highlights the purification of palygorskite and its effects on membrane water permeability in the field of water desalination. © 2021 Society of Chemical Industry (SCI).

Impact of ionic liquid's self-assembly on the crystallization behavior of poly (vinylidene fluoride)

Ionic liquids (IL) are known to act as plasticizer. This work is first report to best of our knowledge, of an amphiphilic ionic liquids (IL), 1-hexadecyl-3-methylimidazolium bromide [C16mim][Br] acting not only as a plasticizer but also as a nucleating agent during crystallization of poly (vinylidene fluoride). With FTIR-ATR, XRD, DSC, and SEM, It is observed that plasticizing and nucleating role of mentioned IL is due to its self-assembling property in fluoropolymer matrix. At 1% loading of [C16mim][Br] in PVDF matrix, it speeds up the crystallization of PVDF accompanied by formation of finger like structure, while at (10%) loading, the formation of micellar structure promote plasticization and PVDF crystallizes at low temperature. Fortunately, in both cases polarized (β/γ) crystal formation is favored.

Poly(vinyl chloride) Asymmetric Membrane Modified with Poly (ethylene glycol): Effect of Additive Concentration on the Morphology and Performance

ABSTRACTAsymmetric membranes of polyvinyl chloride modified with polyethylene glycol as pore former have been prepared by nonsolvent-induced phase separation method using N,N-dimethylacetamide/water as solvent/nonsolvent system. The phase diagram of polyvinyl chloride/polyethylene glycol/N,N-dimethylacetamide/water system showed that polyethylene glycol favors the demixing process. The prepared membrane is characterized by scanning electron microscopy, ATR-FTIR, equilibrium water content, porosity, pure water flux, and contact angle. The addition of polyethylene glycol favored the formation of finger-like structure of polyvinyl chloride membrane initially, and at higher polyethylene glycol concentration, a spongy structure is obtained. The prepared membrane possesses high water flux, excellent thermal stability, and sufficient mechanical strength suitable for ultrafiltration operation.

Study of Polysulfone and Polyacrylic Acid (PSF/PAA) Membranes Morphology by Kinetic Method and Scanning Electronic Microscopy

This work focuses on the study of the morphology forming of Polysulfone (PSf) and polyacrylic acid (PAA) membranes which are prepared by mixing both of the polymers in DMF and the obtained blend is precipitated in water (non-solvent). The precipitation kinetic and the effects of polysulfone concentration, drying-time in free-air and proportions of both polymers are investigated. Based on the SEM technique, the kinetic and viscosity measurements, and the visual observations, this study brings to the fore the different steps of the morphology forming of PSf/PAA membranes: formation of finger-like structures, sponge-like-structures, inner pores, superficial pores and the craters. Appearance of these structures is governed by the exchange process, between casting polymer-solution and the precipitation-bath (coagulation), which is controlled by operating conditions. This work constitutes a great tool in understanding the mechanisms of the morphology forming of PSf/PAA membranes and to improve their performances: preparation of tailored membrane.

YAP IS A CRITICAL AND NOVEL REGULATOR OF MIGRATION AND INVASION AND PREDICTS POOR OUTCOME IN GLIOBLASTOMA

BACKGROUND: Cell migration plays a pivotal role during tissue morphogenesis and homeostasis in multi-cellular organisms. By integrating extracellular cues and intracellular signaling, migration ensures the organized spatial distribution of cells. One of the hallmarks of tumor malignancy is the ability of cells to not only locally invade its surrounding parenchyma but also distally metastasize. Thus, tumors often display a collective sheet of migrating cells which may eventually disseminate and migrate in a single cell manner. To model this phenomenon, we studied the underlying mechanism controlling collective and single cell migration. METHODS: We studied collective and single cell migration in a nanogrooved substratum which mimics reorganized fibrous structures of extracellular matrix. We used our in vivo murine intracranial xenograft model using human GBM cells to study the role of YAP in driving invasive tumor growth. We studied if the YAP-driven cell dispersal mechanisms confer poor patient prognosis in the TCGA and REMBRANDT GBM databases. RESULTS: Using a nanogrooved substratum we observed an epithelial-to-mesenchymal transition-like (EMT-like) behavior with formation of finger-like structures with faster moving marginal cells at the sheet edge. Cells at the tip of these structures frequently lost contact with neighboring cells and disseminated from the original collective cell sheet, which was accompanied by the expression of EMT markers (vimentin and the nuclear translocation of β-catenin). Recently, Yes-associated protein (YAP), a mechanosensor and transcriptional regulator, has been implicated in potentiating migration, invasion, and metastasis; however, the underlying mechanisms remain poorly understood. We observed that YAP is activated in these finger-like projections. We explored mechanisms of YAP-mediated migration and invasion in normal cells and cancer cells where YAP is hyperactive. We found that YAP plays a pivotal role in regulation of this complex migratory and invasive behavior through a novel small Rho-GTPase-dependent signaling mechanism. As with glioblastoma (GBM), metastatic cancers often evade detection because individual cells spread from the primary bulk tumor; thus, making complete resection and treatment impossible. Congruent with our in vitro studies, our in vivo murine model demonstrates the role of YAP in driving invasive tumor growth. We show that these YAP-driven cell dispersal mechanisms confer poor patient prognosis in the TCGA and REMBRANDT GBM databases. CONCLUSIONS: Our findings provide new insights into the biology of aggressive cancers with particular prognostic relevance of this YAP-driven pro-migration and invasion cascade in glioblastoma. In addition, our studies suggest these YAP-dependent mechanisms are evolutionary conserved during development and regeneration and are co-opted by pathological diseases. SECONDARY CATEGORY: Neuropathology & Tumor Biomarkers.

Turbulent mixing of a slightly supercritical van der Waals fluid at low-Mach number

Supercritical fluids near the critical point are characterized by liquid-like densities and gas-like transport properties. These features are purposely exploited in different contexts ranging from natural products extraction/fractionation to aerospace propulsion. Large part of studies concerns this last context, focusing on the dynamics of supercritical fluids at high Mach number where compressibility and thermodynamics strictly interact. Despite the widespread use also at low Mach number, the turbulent mixing properties of slightly supercritical fluids have still not investigated in detail in this regime. This topic is addressed here by dealing with Direct Numerical Simulations of a coaxial jet of a slightly supercritical van der Waals fluid. Since acoustic effects are irrelevant in the low Mach number conditions found in many industrial applications, the numerical model is based on a suitable low-Mach number expansion of the governing equation. According to experimental observations, the weakly supercritical regime is characterized by the formation of finger-like structures – the so-called ligaments – in the shear layers separating the two streams. The mechanism of ligament formation at vanishing Mach number is extracted from the simulations and a detailed statistical characterization is provided. Ligaments always form whenever a high density contrast occurs, independently of real or perfect gas behaviors. The difference between real and perfect gas conditions is found in the ligament small-scale structure. More intense density gradients and thinner interfaces characterize the near critical fluid in comparison with the smoother behavior of the perfect gas. A phenomenological interpretation is here provided on the basis of the real gas thermodynamics properties.

Formation of fingerlike structures in fragmentation of small‐scale patchy aurora

Recent high‐resolution video imagery reveals a dynamic feature of small‐scale (< 20 km) patchy aurora during a substorm recovery phase, that is, fingerlike structures with a few kilometers' scale are formed through the patch fragmentation. Various kinetic processes such as ion finite Larmor radius effects can be involved because the scale mapped into the plasma sheet is much smaller than the ion inertia length. However, such a scale is likely to be strongly damped in a high‐β plasma regime by the ion gyroviscosity effect. In this study, we make several 2.5‐dimensional simulations at the system of each position s along a field line, perpendicular to the ambient magnetic field, by means of the three‐field reduced magnetohydrodynamic equations. The model includes the effects of ion diamagnetic drift and electron parallel motion. In a low‐β regime of s = 4 RE, we find that an ion diamagnetic drift wave grows isotropically to form a patchy structure with a scale of ≈10 km. As the field‐aligned current increases, these patches are fragmented and fingerlike structures with scales of 2–5 km appear owing to the nonlinear electron inertia effect. The scales of patches and fingers and the east–westward finger development, as well as the time scale, are fairly consistent with those of recent observations. On the other hand, at the plasma sheet (ion beta βi = 1, s = 7.5 RE), fingerlike patterns cannot be formed owing to a predominance of large‐scale vortex patterns.

Dynamical rearrangements of the (2×1)O adlayer during CO oxidation on Cu [formula omitted

Scanning tunneling microscopy has been used to visualize dynamical rearrangements of the (2×1)O adlayer on Cu(1 1 0) during reaction with CO. Taking an initially fully oxygen covered surface at 350 K, the reaction starts at terrace edges, where vacant sites for CO adsorption exist. The reaction then proceeds almost uniformly perpendicular to these terrace edges leaving the bare surface behind. In contrast, starting with an initially fully oxygen covered surface at 470 K, the reaction results in the formation of fingerlike structures at the terrace edges. In subsequent images these fingers of bare surface area extend deep into the original adlayer along the [0 0 1] direction, i.e. along the Cu–O–Cu-chains, while the reaction along the [1 1 0] direction, i.e. perpendicular to the chains, appears to proceed uniformly exhibiting a comparatively straight adlayer boundary all the time. The observations are discussed taking into account the complex adsorbate–adsorbate interactions of the Cu–O compounds and the high mobility of these species at 470 K.