28 research outputs found
Copolimerizzazione alternata etilene stirene attivata da catalizzatori ottaedrici del gruppo 4
No full textIsolated ethylene units in isotactic polystyrene chain: stereocontrol of an isospecific post-metallocene titanium catalyst
No full textCopolymerization of styrene with small amounts of ethylene using the catalyst system dichloro[1,4-dithiabutanediyl-2,2'-bis(4,6-di-tert-butyl-phenoxy)] titanium/methylaluminoxane results in the unprecedented formation of isotactic polystyrene containing isolated ethylene units. C-13 NMR spectroscopic analysis of the copolymer indicates that an "enantiomorphic site" control mechanism for isospecific propagation is operating. DSC measurements also indicate the presence of isolated ethylene units which modify the crystallization behavior of the isotactic polystyrene
CAratterizzazione qualitativa del fiume Sele attraverso indagine biologica ed ecotossicologica
No full textAn Ecotoxicological Approach to Evaluate the Environmental Quality of Inland Waters.
No full textWater is traditionally considered a renewable resource as the quantity theoretically available
depends essentially on meteoric water contributions. Modern theories consider river
ecosystem as a central element of the environment but, actually, water ecosystems are more
and more polluted because of agricultural and industrial activities. In Italy, where there is a
widespread urbanization, most part of river ecosystems are exposed to a severe risk of
damage, with consequent loss of biodiversity. The institution of national and regional parks
makes possible the preservation of significant natural value areas. In 1974, the UNESCO
established a “World Network of Biosphere Reserves” (WNBR) aimed to preserve areas,
where there is a close relation between man and nature, through environmental preservation
and sustainable development (UNESCO,2010). Nevertheless, a constant monitoring along the
whole watercourse (from spring to mouth) is needed as, even in a protected area, human
activities could cause, directly or indirectly, damages to valuable ecosystems
An Ecotoxicological Approach to Evaluate the Environmental Quality of Inland Waters
No full textWater is traditionally considered a renewable resource as the quantity theoretically available depends essentially on meteoric water contributions. Modern theories consider river ecosystem as a central element of the environment but, actually, water ecosystems are more and more polluted because of agricultural and industrial activities. In Italy, where there is a widespread urbanization, most part of river ecosystems are exposed to a severe risk of damage, with consequent loss of biodiversity. The institution of national and regional parks makes possible the preservation of significant natural value areas. In 1974, the UNESCO established a “World Network of Biosphere Reserves” (WNBR) aimed to preserve areas, where there is a close relation between man and nature, through environmental preservation and sustainable development (UNESCO,2010). Nevertheless, a constant monitoring along the whole watercourse (from spring to mouth) is needed as, even in a protected area, human
activities could cause, directly or indirectly, damages to valuable ecosystems
Core-shell particles and their application for superhydrophobic surfaces
No full textDuring the last years great effort has been devoted to the fabrication of superhydrophobic surfaces because of their self-cleaning properties. A water drop on a superhydrophobic surface rolls off even at inclinations of only a few degrees while taking up contaminants encountered on its way. rnSuperhydrophobic, self-cleaning coatings are desirable for convenient and cost-effective maintenance of a variety of surfaces. Ideally, such coatings should be easy to make and apply, mechanically resistant, and long-term stable. None of the existing methods have yet mastered the challenge of meeting all of these criteria.rnSuperhydrophobicity is associated with surface roughness. The lotus leave, with its dual scale roughness, is one of the most efficient examples of superhydrophobic surface. This thesis work proposes a novel technique to prepare superhydrophobic surfaces that introduces the two length scale roughness by growing silica particles (~100 nm in diameter) onto micrometer-sized polystyrene particles using the well-established Stöber synthesis. Mechanical resistance is conferred to the resulting “raspberries” by the synthesis of a thin silica shell on their surface. Besides of being easy to make and handle, these particles offer the possibility for improving suitability or technical applications: since they disperse in water, multi-layers can be prepared on substrates by simple drop casting even on surfaces with grooves and slots. The solution of the main problem – stabilizing the multilayer – also lies in the design of the particles: the shells – although mechanically stable – are porous enough to allow for leakage of polystyrene from the core. Under tetrahydrofuran vapor polystyrene bridges form between the particles that render the multilayer-film stable. rnMulti-layers are good candidate to design surfaces whose roughness is preserved after scratch. If the top-most layer is removed, the roughness can still be ensured by the underlying layer.rnAfter hydrophobization by chemical vapor deposition (CVD) of a semi-fluorinated silane, the surfaces are superhydrophobic with a tilting angle of a few degrees. rnrnrnAufgrund der selbstreinigenden Eigenschaft von superhydrophoben Oberflächen wurde in den letzten Jahren viel Arbeit in deren Herstellung gesteckt. Ein Tropfen Wasser perlt von einer um nur wenige Grad geneigten superhydrophoben Oberfläche ab, während er Verunreinigungen auf seinem Weg mitnimmt.rnSuperhydrophobe, selbstreinigende Beschichtungen sind eine mögliche Lösung für den kostengünstigen Erhalt vieler Oberflächen. Idealerweise sind diese Beschichtungen einfach in der Herstellung, mechanisch resistent und Langzeitstabil. Bisher konnte keine Methode gefunden werden alle diese Kriterien zur gleichen Zeit zu erfüllen.rnSuperhydrophobizität steht in direkter Beziehung zur Oberflächenrauigkeit. Das Lotusblatt mit einer zweifach skalierten Oberflächenrauigkeit ist ein Beispiel für eine der effizientesten superhydrophobe Oberflächen.rnIn der vorliegenden Arbeit wurde eine neue Technik zur Herstellung hydrophober Oberflächen vorgestellt. Zwei Längenskalen der Rauheit wurden durch das Aufbringen von Silikapartikel (~ 100 nm im Durchmesser) auf Mikrometer große Polystyrolpartikel durch die bekannte Stöber Synthese dargestellt. Mechanische Stabilität der Partikel wurde durch die dünne Silika Schale auf der Oberfläche der resultierenden „Himbeeren“ erzeugt. Neben der einfachen Darstellung und Handhabbarkeit bieten diese Partikel die Möglichkeit einer verbesserten technischen Anwendung: zum einen sind sie in Wasser dispergierbar und zum anderen können Doppelschichten durch Auftropfmethoden auf selbst sehr rauen Oberflächen erzeugt werden. Die Lösung des Hauptproblems – der Stabilität der Multilagen – liegt im Design der Partikel: Die Schalen, obwohl mechanisch stabil, sind porös genug um Polystyrol aus dem Kern durchzulassen. Im THF Dampf können sich Polystyrolbrücken zwischen den Partikeln ausbilden, die durch das Verkleben der Partikel untereinander für eine Stabilität der Multilagenschicht sorgen. Multilagenschichten sind vielversprechend im Einsatz für kratzbeständige Oberfläche. Wenn die oberste Schicht beschädigt wird, kann die definierte Rauigkeit immer noch durch die darunterliegende Schicht gewährleistet werden. rnChemical Vapour Deposition (CVD) mit semi-fluorierten Silanen bewirkt eine Superhydrophobisierung der Oberflächen mit einem Neigungswinkel von wenigen Grad.rnr
Super liquid repellent coatings against the everyday life wear: Heating, freezing, scratching
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