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Surface Monitoring of Surfactant Phase Separation and Stability in Waterborne Acrylic Coatings
No full textThe stability of a waterborne acrylic coating has been studied paying particular attention to the effects of surfactants (SDS and Triton X-405). In a latex, surfactants are a minor component with respect to the polymer matrix, but they are of fundamental importance in stabilizing the polymer particles in the aqueous medium. When the coating has dried, they exude to the interfaces and self-assemble into hydrophilic aggregates that protrude from the film surface. The surfactant surface distribution has been monitored during thermal and light aging, and the changes observed have been investigated both in terms of the diffusion behavior of low molecular weight molecules in a polymer matrix and in terms of the chemical stability of the surfactants themselves
Novel partially fluorinated copolymers. An evidence of the effect of fluorine on the reactivity of the unfluorinated co-monomer units
No full textA conventional free-radical polymerization of vinyl or propenyl ethers with acrylic or methacrylic monomers with fluorine substitution either in the main chain or in the ester groups has permitted us to obtain a series of copolymers with substantially different fluorine contents and distributions to be obtained. Such copolymers were considered as model compounds to offer new valuable insights as to the influence of fluorinated moieties on the overall stability and, more specifically, on their reactivity with atmospheric oxygen under environmental-like conditions. Depending on the relative position of the fluorine atoms with respect to the common active center of oxidation, the influence ranges from a simple slowing down of the process to a complete redirection towards an otherwise secondary mechanism of oxidation
Three Different ß-Cyclodextrins Direct the Emulsion Copolymerization of a Highly Fluorinated Methacrylate Towards Distinctive Nanostructured Particle Morphologies
No full textStable colloidal dispersions of nanostructured semifluorinated acrylic particles with an unfluorinated core and an
outer layer consisting of copolymers of the highly hydrophobic and lipophobic heptadecafluorodecyl methacrylate (FMA) were
successfully synthesized with the assistance of three different cyclodextrins as phase-transfer catalysts: beta-cyclodextrin (beta-CD),
hydroxypropyl beta-cyclodextrin (HpCD), and methyl beta-cyclodextrin
(MeCD). While all the cyclodextrins form a stable inclusion complex (IC) with FMA, only the ICs with the more hydrophilic HpCD and MeCD are soluble in water. Nevertheless, incorporation of
FMA in the particle shell copolymer could be achieved also when using beta-CD. On the other hand, the morphology of the nanostructured particles was characterized by a ‘‘patchy’’ fluorinated shell dependent on the cyclodextrin used, the best results being obtained with MeCD. A monomer-starved semicontinuous emulsion polymerization procedure was essential to favor the
CD-mediated incorporation of FMA into the copolymer structure and to achieve a stable colloidal dispersion even in the presence of small amounts of mixed anionic–nonionic surfactants. The
thermal and surface properties of the latex films showed a good correlation with the shell composition and patchy nanostructured
morphology of the particles
Heterogeneous fluorinated Latex Films With Controlled Internal Topology For Nanostructured Low-Energy Surfaces
No full textWater-borne organic and hybrid nanostructured polymer particles as film-forming materials for the consolidation and protection of porous substrates
No full textA new class of materials consisting of water-borne formulations (latices) of sub-micron to nano-sized heterophasic particles with film-forming capability has been developed. These latices are prepared by either multi-step sequential emulsion polymerisation, as in the case of partially fluorinated acrylic latices with core-shell particle structure, or by sequential emulsion copolymerisation of acrylates with the reactive comonomer TSPMA (trimethoxysilylpropyl methacrylate) followed by sol-gel co-condensation of various alkoxysilanes onto the pre-formed acrylic particles, yielding hybrid organic-inorganic core-shell particles.
The investigation on the structure, morphology and chemical evolution of these systems during their synthesis and after film formation is aimed at optimising their application properties in the field of the preservation of cultural property. In particular, the unique features resulting from the heterophasic nature of the latex particle can be directed towards the formation of partially fluorinated protective coatings with ultra-hydrophobic surfaces or of new consolidants for porous substrates based on nanostructured hybrid acrylic-organosiloxane materials
Synthetic Approaches to Inorganically Modified Aqueous Polymer Dispersions: from Reactive Acrylic Latexes to Nanostructured Hybrids with either Spherical or Lamellar Inorganic Phase
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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