Depleting state of stratospheric ozoneMohammad Afsar Alam
, 2016, pregledni znanstveni članek
Opis: Though the basic needs of the humans are prioritized first, health and quality of environment are also equally important. Environmental issues are based on many and different things. One of these is the depleting state of Stratospheric Ozone in the atmosphere. The ozone layer is vital to life on earth because it acts as a filter for UV radiation, which can have severe impacts on human health and the earth’s environment. As estimated, every one per cent decrease in the ozone layer results in the increase of ultraviolet light intensity at the earth's surface by two per cent. Known effects of ultraviolet exposure include greater incidence of skin cancer and eye cataracts among humans and diminished crop yields for foods such as peas, beans, and squash and soya beans. Phytoplankton, the tiny one celled Ocean plants that are staple food for squid, fish, seals, and whales also are vulnerable to Ultra violet radiations. Depletion of ozone layer is one of the main issues of the world today. Concerning to these issue two important meetings had been hold i.e. known by the Montreal Protocol and Vienna Convention. Most of the world countries are part of this Montreal Protocol and Vienna Convention. Eritrea is also part of Montreal Protocol and Vienna Convention. In the present paper basically an attempt has been made to show the world’s concern in general and the Eritrea’s in particular about the conservation measures taken on mitigation of Ozone layer. This research paper also emphasizes on the global problem of Ozone Depleting Substances (ODSs) releasing from different industries and specific sources. Besides, the study further includes the existence of naturally created Ozone hole on the Polar Regions.
Ključne besede: ozone layer, depletion, chlorofluorocarbons, CFCs, environment
Objavljeno: 17.04.2018; Ogledov: 455; Prenosov: 64
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Aquaporin-based biomimetic polymeric membranesJoachim Habel
, Michael R. Hansen
, Søren Kynde
, Nanna Larsen
, Søren Roi Midtgaard
, Grethe Vestergaard Jensen
, Julie Bomholt
, Anayo Ogbonna
, Kristoffer Almdal
, Alexander Schulz
, Claus Hélix-Nielsen
, 2015, pregledni znanstveni članek
Opis: In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes.
Ključne besede: aquaporins, biomimetic membranes, block copolymers, proteopolymersomes, polyhedral oligomeric silsesquioxanes, polyamide layer, microfluidics, membrane proteins, protein-polymer-interactions
Objavljeno: 21.06.2017; Ogledov: 825; Prenosov: 77
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STRUCTURING OF SOL-GEL FUNCTIONALIZED CELLULOSE HYBRID MATERIALS AND THEIR CHARACTERIZATIONHeike M. A. Ehmann
, 2012, doktorska disertacija
Opis: The goal of this thesis is the structuring of cellulose nanocrystals using different organofunctional silane compounds and different cationic species to prepare highly functional materials with tailored properties. In addition different new aspects and approaches for the structural characterization of functionalised cellulose nanocrystals (CNC) functionalised with different organofunctionalalkoxysilanes as well as cationic species have been introduced.
Cellulose nanocrystals (CNC) are prepared using three different acidic conditions to hydrolyse microcrystalline cellulose (MCC). The sulphuric acid hydrolysis introduces highly negative charged sulphate groups on the CNC. The aqueous nanocrystalline cellulose suspensions (aNCS) are analysed in terms of ζ-potential related to the pH and concentration to investigate the stability while dynamic light scattering (DLS) is used to investigate the size distribution. The hydrochloric acid hydrolysis in contrast only removes the amorphous regions but the so obtained CNC are less stabilized (decreased ζ-potential) and tend to agglomerate very fast. The use of the mixture of both acids (HCl and H2SO4) during the hydrolysis of MCC introduces less sulphate groups compared with the sulphuric acid hydrolysis. AFM investigations show that the shapes of the CNC are highly influenced by the hydrolysis conditions. While the shape of the H2SO4 hydrolysed CNC is rod like, while the shape of the other two CNC samples is more spherical in nature. One of the major topic in this work is the analysis of aNCS in aqueous solutions by small angle x-ray scattering (SAXS). The use of the generalized indirect Fourier transformation (GIFT) method allows the analysis of these systems and structural properties such as shape, size and surface charge of aNCS can be assessed. Using this kind of characterisation it can be seen that the shape of the H2SO4 hydrolysed CNC is definitely rod like while the other CNC sample can be described with spheres. In addition to the aNCS characterisation different substrates (Si-wafer, glass slides, polystyrene, etc.) are equipped with aNCS using a variety of different deposition methods (e.g. spin coating, solution casting, dip coating). The resulting films are studied in terms of morphology AFM, SARFUS and SEM. Sophisticated scattering techniques are employed for surface structural characterisation as grazing incidence small angel x-ray scattering. The determination of surface free energies allows conclusions about the hydrophilicity and hydrophobicity as well as the interaction capacity with different liquids. It can be seen that besides the hydrophilic nature of the CNC also hydrophobic interactions are present. The highly negative charged CNC sample which was prepared using sulphuric acid hydrolysis is found to be best suitable for the further hybridization with different organofunctional silanes and for the layer by layer approach (LBL) with different cationic species.
The organofunctionalalkoxysilanes which were used in this study can be divided into three groups (e.g filler, surface functionalisation silanes, cross linking silanes). Depending on the nature of the organic residue the silanes are capable to introduce functionalities with enhanced hydrophobic and olephobic properties. The surface energies are investigated using contact angle method, while the surface energies are calculated using three different model approaches (OWRK, Wu, Acid-Base). The most increased hydrophobic and oleophobic properties were measured for trimethylfluorophenylsilantriol (PFTEOS). The morphology of the coated silanes is investigated using SAFRUS technique. It can be seen that nearly all silanes can be coated as homogeneous films onto different substrates (Si-wafer, SURFs, glass slides) with different methods (spin coating, solution casting). The macroscopic appearance of solution casted silanes is investigated using optical microscopy. The differences of the structural nature of the so obtained coatings and detaching films were investigated...
Ključne besede: Cellulose nanocrystals, sol-gel chemistry, organofunctionalalkoxysilanes, hybrid materials, small angle x-ray scattering, generalized indirect Fourier Transformation, quartz crystal microbalance dissipation, surface free energy, surface functionalisation, layer by layer
Objavljeno: 28.11.2012; Ogledov: 1866; Prenosov: 121
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Electrokinetic investigation of polyelectrolyte adsorption and multilayer formation on a polymer surfaceStefan Köstler
, Volker Ribitsch
, Karin Stana-Kleinschek
, Georg Jakopic
, Simona Strnad
, 2005, izvirni znanstveni članek
Opis: Self assembled polyelectrolyte layers of poly(sodium 4-styrenesulfonate) (PSS), and poly(diallyldimethylammonium chloride) (PDADMAC) were deposited on planar poly(ethylene terephthalate) (PET) substrates using the layer-by-layer technique. Charged functional groups were generated on the polymer substrates by means of a surface modification procedure prior to polyelectrolyte adsorption. The layers were characterised concerning their electrokinetic properties. The build-up of multilayer architectures could be followed by changes of the zeta-potential versus pH curves. An increase of coating density with increasing layer number was found. The electrokinetic properties of the PET substrates were not recognised anymore if more then four layers were applied. If PSS formed the outermost layer these assemblies were very stable against shear forces while if PDADMAC formed the outermost layer the films were partially destroyed by high shear forces.
Ključne besede: textile materials, polyelectrolyte multilayers, layer-by-layer assembly, zeta-potential, ellipsometry, polymer substrate, layer stability
Objavljeno: 01.06.2012; Ogledov: 1633; Prenosov: 64
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Zeta potential determination of polymeric materials using two differently designed measuring cells of an electrokinetic analyzerHermina Bukšek
, Thomas Luxbacher
, Irena Petrinić
, 2010, izvirni znanstveni članek
Opis: The so-called zeta potential can be determined through electrokinetic measurements and indicates the status regarding surface charges along the interface between solids and liquids. Surface charge gives us information about the condition, quality, and characteristics of a macroscopic surface in the polar medium. In our study the zeta potential was determined using a 'SurPASS' electrokinetic analyzer based on the streaming current and streaming potential measurements. The aim of the research was to compare the results of two differently designed measuring cells ('Adjustable Gap Cell' and 'Clamping Cell') but operating on the same principle. In order to investigate this problem, the zeta potential was determined for the three polymeric materials: poly(ethylene terephthalate) foil, thin-film polyamide composite membranes for nanofiltration and reverse osmosis. The results obtained with 'Clamping Cell' versus 'Adjustable Gap Cell' showed differences in zeta potential, where the 'Adjustable Gap Cell' gave more reproducible results. One reason for this behaviour could be the different geometries of the streaming channels. A more likely reason is the design of the 'Clamping Cell', that requires a sample size larger than necessary for zeta potential determination.
Ključne besede: electrical double layer, zeta potential, electrokinetic analyser, streaming current potential, polymeric materials
Objavljeno: 31.05.2012; Ogledov: 1150; Prenosov: 92
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