Photoresponsive poly(methyl methacrylate)‐b‐azodendron block copolymers prepared by ATRP and click chemistry

A range of block copolymers (BCs) consisting of a linear poly(methyl methacrylate) (PMMA) block linked to an aliphatic polyester dendron functionalized with azobenzene moieties have been synthesized by sequential atom transfer radical polymerization (ATRP) and Click Chemistry. Two alkyne‐functionalized PMMA homopolymers with different molecular weights were obtained by ATRP and coupled to generations 2 to 4 of azodendrons bearing an azide group at the focal points. In the case of the azodendron with the highest generation number, the length of the flexible spacer attaching the cyanoazobenzene units to the dendron has also been modified. The coupling of both blocks and purity of BCs were checked by gel permeation chromatography, nuclear magnetic resonance, and infrared spectroscopy. The thermal transitions and liquid crystalline behavior of the BCs were investigated by differential scanning calorimetry and polarized‐light optical microscopy. A morphological study was carried out by transmission electron microscopy, using samples annealed at 115 °C. Photo‐induced anisotropy was induced in thin films of these materials after annealed at 115 °C. The highest stable birefringence values were obtained for the BCs bearing 8 and 16 azobenzene units in the dendritic block. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1538–1550, 2010     

Onset of oscillatory binary fluid convection in three-dimensional cells

The purpose of this work is to investigate the influence of the transverse walls on the onset of convection in a horizontal rectangular cavity of infinite length filled with a binary mixture when heated from below. For the first time we take into account the effect of the third dimension without making any approximation and considering realistic boundary conditions. In previous numerical works the width of the cell was either taken to be infinity (bulk mixtures) or different approximations usually valid in the narrow cell limit were assumed (i.e., Hele–Shaw and non-ideal Hele–Shaw approximations). The results we find show that the presence of the walls has a considerable effect on the onset of convection even for intermediate transverse aspect ratio cells. They also show that the approximations generally assumed fail to reproduce the correct behaviour of the critical parameters in an important range of aspect ratio values when the primary bifurcation is oscillatory. We have compared the critical values of the Rayleigh number and the frequency with those reported in the literature (Ohlsen et al. [1]) and we find a quantitative agreement within the experimental error. PACS 47.20.Bp, 47.27.Te, 47.54.+r     

A Magnetic Ionic Liquid Based on Tetrachloroferrate Exhibits Three‐Dimensional Magnetic Ordering: A Combined Experimental and Theoretical Study of the Magnetic Interaction Mechanism

A new magnetic ionic liquid (MIL) with 3D antiferromagnetic ordering has been synthetized and characterized. The information obtained from magnetic characterization was supplemented by analysis of DFT calculations and the magneto‐structural correlations. The result gives no evidence for direct iron‐iron interactions, corroborating that the 3D magnetic ordering in MILs takes place via super‐exchange coupling containing two diamagnetic atoms intermediaries.     

Synthesis,characterization and photoinduction of optical anisotropy in liquid crystalline diblock azo‐copolymers

Diblock copolymers with polymethyl methacrylate and side chain liquid crystalline (LC) azopolymethacrylate blocks were synthesized by atom transfer radical polymerization (ATRP). The azobenzene content in these copolymers ranges from 52 to 7 wt %. For an azo content down to 20% they exhibit a LC behavior similar to that of the azo homopolymers. Thin films of these copolymers were characterized by transmission electron microscopy (TEM). A lamellar nanostructure was observed for azo content down to 20 wt %, while no structure is observed for the copolymer with a 7% azo content. The optical anisotropy induced in these films by illumination with linearly polarized 488 nm light was studied and the results compared with those of the azo homopolymer and of a random copolymer with a similar composition. The formation of azo aggregates inside the azo blocks is strongly reduced in going from the homopolymer to the copolymers. Photoinduced azo orientation perpendicular to the 488 nm light polarization was found in all the polymers. The orientational order parameter is very similar in the homopolymer and in the block copolymers with an azo content down to 20 wt %, while it is much lower in the random copolymer and in the 7 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1899–1910, 2007     

Ultrafast dynamics of photoionized acetylene

Acetylene cations [HCCH](+) produced in the A(2)Σ(g)(+) state by extreme ultraviolet (XUV) photoionization are investigated theoretically, based on a mixed quantum-classical approach. We show that the decay of the A(2)Σ(g)(+) state occurs via both ultrafast isomerization and nonradiative electronic relaxation. We find a time scale for hydrogen migration and electronic decay of about 60 fs, in good agreement with recent XUV-pump/XUV-probe time-resolved experiments on the same system [Phys. Rev. Lett. 105, 263002 (2010)]. Moreover, we predict an efficient vibrational energy redistribution mechanism that quickly transfers excess energy from the isomerization coordinates to slower modes in a few hundred femtoseconds, leading to a partial regeneration of acetylenelike conformations.     

Preparation of side‐chain liquid crystalline Azopolymers by CuAAC postfunctionalization using bifunctional azides: Induction of chirality using circularly polarized light

Well‐defined side‐chain liquid crystal azopolymers have been synthesized by click chemistry of poly(propargyl methacrylate) with bifunctional liquid crystalline azides to produce materials with large degrees of functionalization. A polymeric scaffold having pendant alkyne groups was prepared by atom transfer radical polymerization (ATRP) and postfunctionalized by copper(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) using homo‐ and heterobifunctional azides. The azides are derivatives of 2,2‐bis(hydroxymethyl)propanoic acid (bis‐MPA) containing photoresponsive azobenzene and/or liquid crystalline biphenyl moieties. The approach is a convenient alternative to increase the density of functional units in side‐chain polymers having moderate polymerization degrees and to modulate the properties of the final material. The article describes the synthesis, characterization, and liquid crystalline properties of the obtained polymers. The effect of the chemical structure and the possible cooperative effects between functional units in the photo‐induction of chirality are also evaluated. A switchable photo‐transference of chirality from the circularly polarized light (CPL) to material has been achieved. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Punctured combinatorial Nullstellensätze

In this article we extend Alon’s Nullstellensatz to functions which have multiple zeros at the common zeros of some polynomials g ₁,g ₂, …, g _n , that are the product of linear factors. We then prove a punctured version which states, for simple zeros, that if f vanishes at nearly all, but not all, of the common zeros of g ₁(X ₁), …,g _n (X _n ) then every residue of f modulo the ideal generated by g ₁, …, g _n , has a large degree.     

Tracking fin whale calls offshore the Galicia Margin, North East Atlantic Ocean

Data recorded during a temporary deployment of ocean bottom seismometers (OBSs) are used in this study to monitor the presence of fin whales around the array. In the summer of 2003, ten OBSs were placed 250 km from the NW coast of Iberia in the Galicia Margin, NE Atlantic Ocean for a period of one month. The recorded data set provided a large variety of signals, including fin whale vocalizations identified by their specific acoustic signature. The use of a dense array of seafloor receivers allowed investigation into the locations and tracks of the signal-generating whales using a seismological hypocentral location code. Individual pulses of different sequences have been chosen to study such tracks. Problems related to the correct identification of pulses, discrimination between direct and multiple arrivals, and the presence of more than one individual have been considered prior to location. Fin calls were concentrated in the last two weeks of the deployment and the locations were spread around the area covered by the array. These results illustrate that, besides its classical seismological aim, deployment of semipermanent seafloor seismic arrays can also provide valuable data for marine mammal behavior studies.