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Azo-containing polymer brushes: photoalignment and application as command surfaces
No full textBrush polymer surfaces, with respect to traditional films, are resistant to solvents and to high temperatures due to the covalent bonds between chain and substrate, which stabi!izes the film morphology [ The photo response of films of azopolymers has extensively been characterised [ either as cast films [ or Langmuir-Blodgett films [ However the peculiar characteristics of polymeric brushes, with the possibility of a fine control on the struct-ure, make them very attractive for application as command surfaces.
A brush polymer containing photosensitive mesogenic side chains has been directly synthesised on glass and on silicon substrates by a grafting method involving polymerisation of the methacrylic azobenzenic monomer (4-methacryloyloxy- hexyloxy-4’-ethoxyazobenzene) under Atomic Transfer Radical Polymerisation (ATRP) conditions.
Under these conditions the polymeric brush grows linearly with the reaction time; the polymerisation therefore could be considered as living, and these molecular brushes could be emp!oyed for making new biock copolymeric brushes.
Different chain lengths have been obtained by fine tuning of the time of polymerisation. Brush growth was monitored by a combination of UV/vis absorbance and by nuil ellipsometry (see figure 2); the resulting structure was characterised by Atomic Force Microscopy, optical dichroism and confocai depolarised micro-Rarnan spectroscopy to measure the degree of molecular order.
Both photomechanical effects (photoinduced expansion and shrinking) and photoaligment in the brush have been investigated as a function of temperature, illuminatìon and brush length. The resuits have been compared with those obtained by a parallei study carried out on spin—coated films of polymers composed by the same monomer and with high molecular weight.
We then employed such brushes as photo controllable command surfaces in twistedlplanar switchabie iiquid crystal cells. An exampie of such celi is shown in figure 3; the celi was fihled with cyanobiphenyi 5CB, the command surface was provided by a polymeric brush (length i2nm) grown on glass while the reference surface was provided by rubbed polyimmide. The celi was prepared as twisted by macroscopic polarised illumination, while selected spots were reverted to pl
Figure 3 Polarising opticai microscopy images ofLC celi (1000x800 im)
These cells have been characterised by depolarised confocal micro Raman spectroscopy. The order parameter at the command surface has been measured as a function irradiation and brush length. The results are compared with those obtained on similar cells [
References
[ T. Kowaiewski, R.D. McCuilough, and K. Matyjaszewski, Eur. Phys. i E 10, 5—16 (2003)
[ A. Natansohn and P. Rochon, Chem. Rev. 102, 4139-4176 (2002)..
[ P. Camorani, M.P. Fontana Phys. Rev. E 73, 011703 (2006)
[ L. Cristofolini, S. Ari, M. P. Fontana, Phys. Rev. Lelters 85 4912 (2000).
[ P.Camorani, M.P. Fontana, Mol CrystLiq Cryst, 465, 143 (2007
Optical bit stability and relaxation processes in a liquid crystal polymer with a photosensitive azo dye molecule as side group
No full textPhotoinduced dynamics in a photosensitive side chain polymeric liquid crystal by quasielastic and inelastic neutron scattering
No full textAnalisi dell'esposizione a radiazione non ionizzante da radar meteorologico
No full textLa valutazione dell’esposizione a radiazioni non ionizzanti a radiofrequenze e microonde sia della popolazione che del personale professionalmente addetto, viene considerata un settore emergente delle indagini ambientali e di sicurezza sul lavoro. Ciò é dovuto al notevole incremento delle sorgenti di campi elettromagnetici ed alla loro variegata tipologia alla cui installazione si é assistito negli ultimi anni, eminentemente per finalità di comunicazioni mobili o di radiotelediffusione. Una categoria di sorgenti scarsamente indagata per le note difficoltà involte nella misura, oltre alle implicazioni di inaccessibilità e/o di segretezza di alcune installazioni, sono i radar, siano essi di sorveglianza aerea e marittima o meteorologici. In questo lavoro sono state analizzate le emissioni del radar meteorologico dell’autorità di bacino del fiume Adige, gestito congiuntamente dalle province di Trento e Bolzan
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
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