487 research outputs found
Nanostructured Films of Amphiphilic Fluorinated Block Copolymers for Fouling Release Application
No full textNew amphiphilic block copolymers SnSzm consisting of blocks with varied degrees of polymerization, n and m,
of polystyrene, S, and polystyrene carrying an amphiphilic polyoxyethylene-polytetrafluoroethylene chain side-group,
Sz, were prepared by controlled atom transfer radical polymerization (ATRP). The block copolymers, either alone
or in a blend with commercial SEBS (10 wt% SEBS), were spin-coated in thinner films (200-400 nm) on glass and
spray-coated in thicker films (about 500 nm) on a SEBS underlayer (150-200 μm). Angle-resolved X-ray photoelectron
spectroscopy (XPS) measurements proved that at any photoemission angle, φ, the atomic ratio F/C was larger than
that expected from the known stoichiometry. Consistent with the enrichment of the outer film surface (3-10 nm) in
F content, the measured contact angles, θ, with water (θw = 107°) and n-hexadecane (θh = 64°) pointed to the
simultaneous hydrophobic and lipophobic character of the films. The film surface tension γS calculated from the θ
values was in the range 13-15 mN/m. However, the XPS measurements on the “wet” films after immersion in water
demonstrated that the film surface underwent reconstruction owing to its amphiphilic nature, thereby giving rise to
a more chemically heterogeneous structure. The atomic force microscopy (AFM) images (tapping mode/AC mode)
revealed well-defined morphological features of the nanostructured films. Depending on the chemical composition
of the block copolymers, spherical (ca. 20 nm diameter) and lying cylindrical (24-29 nm periodicity) nanodomains
of the S discrete phase were segregated from the Sz continuous matrix (root-mean-square, rms, roughness ≈ 1 nm).
After immersion in water, the underwater AFM patterns evidenced a transformation to a mixed surface structure, in
which the nanoscale heterogeneity and topography (rms ) 1-6 nm) were increased. The coatings were subjected to
laboratory bioassays to explore their intrinsic ability to resist the settlement and reduce the adhesion strength of two
marine algae, viz., the macroalga (seaweed) UlVa linza and the unicellular diatom NaVicula perminuta. The amphiphilic
nature of the copolymer coatings resulted in distinctly different performances against these two organisms. UlVa
adhered less strongly to the coatings richer in the amphiphilic polystyrene component, percentage removal being
maximal at intermediate weight contents. In contrast, NaVicula cells adhered less strongly to coatings with a lower
weight percentage of the amphiphilic side chains. The results are discussed in terms of the changes in surface structure
caused by immersion and the effects such changes may have on the adhesion of the test organisms
From logistiké to logistique: the long travel of a word
No full textThis paper aims to follow some of the key stages that the term logistiké passed through thanks to the double meaning it received since its appearance in ancient Greece: a more technical one (i.e. reckoning) and a more general one (i.e. reflecting, thinking). Taking as a starting point the Pythagorean Archytas, the discussion will take into account Plato’s very influential contribution, its developments, the modern age with a special focus on Leibniz, and the revival of the notion in French in 19th century
Amphiphilic block copolymer/PDMS blends and nanocomposites for release coatings of Ulva
No full textAmphiphilic diblock copolymers, Sz6 and Sz12, consisting of a polydimethylsiloxane block (average degree of polymerisation = 132) and a PEGylated−fluoroalkyl modified polystyrene block (Sz, average degree of polymerisation = 6, 12) were prepared by ATRP. Coatings were obtained from blends of either block copolymer (1–10 wt%) with a PDMS matrix. The coating surface presented a simultaneous hydrophobic and lipophobic character, owing to the strong surface segregation of the lowest surface energy fluoroalkyl chains of the block copolymer. Surface chemical composition and wettability of the films were affected by exposure to water. Block copolymer Sz6 was also blended with PDMS and a 0.1 wt% amount of multiwall carbon nanotubes (CNT). The excellent fouling-release properties of these new coatings against the macroalga Ulva linza essentially resulted from the inclusion of the amphiphilic block copolymer, while the addition of CNT did not seem to improve the fouling-release properties
Amphiphilic block copolymer/poly(dimethylsiloxane) (PDMS) blends and nanocomposites for improved fouling-release
No full textAmphiphilic diblock copolymers, Sz6 and Sz12, consisting of a poly(dimethylsiloxane) block (average degree of polymerisation 132) and a PEGylated-fluoroalkyl modified polystyrene block (Sz, average degree of polymerisation = 6, 12) were prepared by atom transfer radical polymerization (ATRP). Coatings were obtained from blends of either block copolymer (1-10 wt%) with a poly(dimethylsiloxane) (PDMS) matrix. The coating surface presented a simultaneous hydrophobic and lipophobic character, owing to the strong surface segregation of the lowest surface energy fluoroalkyl chains of the block copolymer. Surface chemical composition and wettability of the films were affected by exposure to water. Block copolymer Sz6 was also blended with PDMS and a 0.1 wt% amount of multiwall carbon nanotubes (CNT). The excellent fouling-release (FR) properties of these new coatings against the macroalga Ulva linza essentially resulted from the inclusion of the amphiphilic block copolymer, while the addition of CNT did not appear to improve the FR properties
La posizione del verbo in vedico
No full textIl saggio si occupa della descrizione sintattica della posizione del verbo vedico nel quadro della teoria Split-CP. Delbrück (1878) aveva già individuato la struttura di base SOV e l’esistenza di costruzioni marcate. Qui si cerca di precisare ulteriormente quali sono i contesti che provocano il movimento del verbo verso la periferia sinistra della frase: focalizzazioni contrastive e non contrastive, dello stesso verbo o di argomenti da questo dipendenti. L’area occupata dai costituenti marcati corrisponde alla proiezione CP che il Cartographic Program ha analizzato in più proiezioni funzionalmente differenziate
A comparison between different fouling-release elastomer coatings containing surface-active polymers
No full textSurface-active polymers derived from styrene monomers containing siloxane (S), fluoroalkyl (F) and/or ethoxylated (E) side chains were blended with an elastomer matrix, either poly(dimethyl siloxane) (PDMS) or poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), and spray-coated on top of PDMS or SEBS preformed films. By contact angle and X-ray photoelectron spectroscopy measurements, it was found that the surface-active polymer preferentially populated the outermost layers of the coating, despite its low content in the blend. However, the self-segregation process and the response to the external environment strongly depended on both the chemistry of the polymer and the type of matrix used for the blend. Additionally, mechanical testing showed that the elastic modulus of SEBS-based coatings was one order of magnitude higher than that of the corresponding PDMS-based coatings. The coatings were subjected to laboratory bioassays with the marine alga Ulva linza. PDMS-based coatings had superior fouling-release properties compared to the SEBS-based coatings
Characterising the permeability and structure of fluid-escape conduits in sedimentary basins - application to geological carbon sequestration
No full textIncreased greenhouse gas emissions entering the atmosphere and hydrosphere are causing changes to global climate. Geological carbon sequestration is a proven technology, used to reduce anthropogenic emissions from the atmosphere. However, there are concerns about the unintended migration of CO2 from sub-surface storage reservoirs. Fluid-escape structures, which act as conduits for pressure-driven fluids, are observed in sedimentary basins globally. These structures can extend over 500 m across and intrude vertically through kilometres of sedimentary overburden. The quantitative assessment and nature of fluid-escape conduits are currently poorly constrained. Here we sample and characterise analogous onshore field outcrop analogues in Panoche Hills, California and Varna, Bulgaria to complement the study of active structures in the Witch Ground Basin, Central North Sea. A key aim is to quantify permeability and determine the process mechanisms of fluid flow through focused fluid conduits. Here we generate an accurate, repeatable and upscalable 3D X-ray micro-computed tomography (XCT) image-based methodology workflow to calculate porosity, effective porosity, and permeability of fluid-escape conduit samples. During fieldwork and sampling, the geometry, distribution, physical interaction with host-rocks and 3D properties are determined. Given the large scale of the structures (>150 m wide), porosity and permeability transects are performed across the intrusions and their host sediments, to characterise natural variability and identify preferential fluid flow pathways.
Studies of sand intrusions in the Panoche Hills reveal permeability heterogeneity is largely controlled by silica cementation processes linked to the drainage of pore waters from silica-rich host rock sediments during intrusion formation. Sub-vertically orientated intrusions have reduced permeability due to the incorporation of clay and silt host rock sediments into the matrix of intrusions, and subsequent dewatering, grain compaction and silica Opal-A to Opal-CT transformation. Further, the investigation of fluid-escape structures in Varna and Panoche Hills highlights a three orders of magnitude reduction in permeability of unconsolidated host rock sediments caused by the transformation of methane gas by anaerobic oxidation to carbonates. The mapping of carbonate pipes revealed that focused fluid flow process mechanisms are not restricted to fine-grained host rock strata, and can occur in unconsolidated sediments.
High-resolution 2D and 3D seismic reflection data, integrated with sediment core data, are used to characterise the Scanner Pockmark Complex, Central North Sea. The study has revealed that gas flows vertically upwards through chimneys, directly observed as a series of interconnected fractures. Previous studies interpret seismic chimneys as vertical conduits in hydraulic connection to a single, deeper zone of overpressured fluid. Here we observe that fluid overpressure generation, leading to chimney and pockmark genesis, represents a complex system with gas-bearing zones at multiple depth intervals. When integrated into a multi-disciplinary approach, these findings can improve our understanding of focused fluid flow within the shallow overburden, for applications to shallow geohazard assessment and carbon sequestration
Fluorinated/siloxane copolymer blends for fouling release: chemical characterisation and biological evaluation with algae and barnacles
No full textFouling-release coatings were prepared from blends of a fluorinated/siloxane copolymer with a poly(dimethylsiloxane) (PDMS) matrix in order to couple the low modulus character of PDMS with the low surface tension typical for fluorinated polymers. The content of the surface-active copolymer was varied in the blend over a broad range (0.15-10 wt % with respect to PDMS). X-ray photoelectron spectroscopy depth profiling analyses were performed on the coatings to establish the distribution of specific chemical constituents throughout the coatings, and proved enrichment in fluorine of the outermost layers of the coating surface. Addition of the fluorinated/siloxane copolymer to the PDMS matrix resulted in a concentration-dependent decrease in settlement of barnacles showed that adhesion strength on the fluorinated/siloxane copolymer was significantly lower than the siloxane control. However, differences in adhesion strength were not directly correlated with the concentration of copolymer in the blends
The rate of extreme coronal line emitters in the Baryon Oscillation Spectroscopic Survey LOWZ sample
No full textJ. Callow et al.Extreme coronal line emitters (ECLEs) are a rare class of galaxy that exhibit strong, high-ionization iron coronal emission lines in their spectra. In some cases, these lines are transient and may be the result of tidal disruption event (TDEs). To test this connection, we calculate the rate of variable ECLEs (vECLEs) at redshift. We search for ECLEs in the Baryon Oscillation Spectroscopic Survey (BOSS) LOWZ sample and discover two candidate ECLEs. Using follow-up spectra from the Dark Energy Spectroscopic Instrument and Gemini Multi-Object Spectrograph, and mid-infrared observations from the Wide-field Infrared Survey Explorer, we determine that one of these galaxies is a vECLE. Using this galaxy, we calculate the galaxy-normalized vECLE rate at redshift to be and the mass-normalized rate to be. This is then converted to a volumetric rate of. Formally, the LOWZ vECLE rates are times lower than the rates calculated from the Sloan Digital Sky Survey Legacy sample at redshift. However, given the large uncertainties on both measurements, they are consistent with each other at. Both the galaxy-normalized and volumetric rates are one to two orders of magnitude lower than TDE rates from the literature, consistent with vECLEs being caused by per cent of all TDEs.This work was supported by the Science and Technology Facilities Council [grants ST/S000550/1 and ST/W001225/1]. Funding for the Sloan Digital Sky Survey (SDSS) and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, and the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Website is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, The University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of High-Energy Physics, under Contract no. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract. Additional support for DESI was provided by the U.S. National Science Foundation (NSF), Division of Astronomical Sciences under Contract No. AST-0950945 to the NSF’s National Optical-Infrared Astronomy Research Laboratory; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising–Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Humanities, Science and Technology of Mexico (CONAHCYT); the Ministry of Science, Innovation and Universities of Spain (MICIU/AEI/10.13039/501100011033), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the U. S. National Science Foundation, the U. S. Department of Energy, or any of the listed funding agencies. This research has made use of NASA’s Astrophysics Data System Bibliographic Services and the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration (NASA) and operated by the California Institute of Technology. This publication also makes use of data products from NEOWISE, which is a project of the Jet Propulsion Laboratory/California Institute of Technology, funded by the Planetary Science Division of NASA. The CRTS survey is supported by the U.S. National Science Foundation (NSF) under grants AST-0909182 and AST-1313422.Peer reviewe
PDMS network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)-fluoroalkyl side chains for fouling release coatings. II. Laboratory assays and field immersion trials
No full textAmphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), performance being equivalent to a coating based on Intersleek 700TM. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance
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