Unexpected giant elasticity in side-chain liquid-crystal polymer melts: A new approach for the understanding of shear-induced phase transitions

International audienceRecent studies have revealed that high molecular weight liquid crystals typically exhibit shear induced phases within the isotropic melt. From rheo-birefringence measurements, we demonstrate that those shear induced phases are not coupled with conventional orientational-order fluctuations. From rheo-SANS experiments, we show that the polymer chain is deformed at time scales longer than the viscoelastic relaxation time. Finally, careful visco-elastic measurements reveal a strong elastic behaviour; the melt is not a viscoelastic liquid but solid-like at equilibrium one hundred degrees over the glass transition temperature and up to 15°C over the Isotropic-Nematic phase transition. This supra molecular cohesion and its extra long relaxation times may explain the emergence of non-linear phenomena

Studying Dispersed Phase Holdup in a Pilot Plant Agitated Liquid–liquid Mixer by Developing Online Expanded Laser Beam based Technique

Expanded Laser Transmission Technique (E-LTT), where a laser beam is used in conjunction with a beam expander large enough to cover the average drop size up to a few millimeters in the path of the laser in a liquid–liquid dispersion mixture, has been applied for online continuous measurement and investigation in a non-invasive manner of the drop phase volume fraction in an agitated flow mixer of a pilot plant scale. The limitations of beam scattering by the drops through the dispersion path were overcome by having liquids of matching refractive indices enabled by the temperature control system. This study reports for the first time the continuous measurements of the line averaged dispersed phase holdup for a pilot plant scale liquid–liquid mixer equipped with a commercial design mixer, where the measurements have no limitations to the geometrical aspects. Experimental results from a cubic mixing tank with a dispersion depth of 30cm were discussed. Online measurements were carried out in the presence of a revolving impeller and transmission of the expanded laser beam. The net volume of the mixer was 20.42liter, and the dispersed phase holdup that was successfully measured ranged between 0.15 and 0.75. In this work, arrangement of the laser setup was made to scan and measure continuously the line average dispersed phase holdup along the height of the pilot plant scale of the flow agitated liquid–liquid mixer. The E-LTT measurements were validated by comparing their results with those obtained from the mixer by shut-down procedure

The frozen state in the liquid phase of side-chain liquid-crystal polymers

International audienceQuenched isotropic melts of side-chain liquid-crystal polymers reveal surprisingly an anisotropic polymer conformation. This small-angle neutron-scattering (SANS) result is consistent with the identification of a macroscopic, solidlike response in the isotropic phase. Both experiments (rheology and SANS) indicate that the polymer system appears frozen on millimeter length scales and at the time scales of the observation. This result implies that the flow behavior is not the terminal behavior and that cross-links or entanglements are not a necessary condition to provide elasticity in melts

Mendil et al Reply

International audienceIn the preceding Comment [1], Collin and Martinoty claim that a conventional flow behavior (G' ~ f2 , G'' ~ f) is obtained at 20 $\mu$m gap thickness, for a LC-polymer (LCP105) in the nematic phase, using a filling with a capillary, whereas a solidlike behavior (G' ~ Cst, G" ~ Cst) is observed by approaching two parallel surfaces to the sample (as we apply in our experiment). Our observations of a terminal solidlike behavior are thus interpreted by Collin and Martinoty as an anomaly induced by compression effects. We clearly refute this interpretation. We note that, on Fig. 13 and 14 of a previous paper written by Collin and Martinoty [2], they report no more a conventional flow but an elastic behavior at lower temperature using the capillary filling and the same polymer (LCP105). Their previous observations are thus in contradiction with their present purpose; i.e., a terminal flow behavior

Richness of side-chain liquid-crystal polymers: From isotropic phase towards the identification of neglected solid-like properties in liquids

International audienceVery few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the isotropic phase of SCLCP melts challenges the conventional timescales described in theoretical approaches and reveal very long timescales, neglected until now. This spectacular behavior is the starter of the present survey that reveals long range solid-like interactions up to the sub-millimetre scale. We address the question of the origin of this solid-like property by probing more particularly the non-equilibrium behavior of a polyacrylate substituted by a nitrobiphenyl group (PANO2). The comparison with a polybutylacrylate chain of the same degree of polymerization evidences that the solid-like response is exacerbated in SCLCPs. We conclude that the liquid crystal moieties interplay as efficient elastic connectors. Finally, we show that the " solid " character can be evidenced away from the glass transition temperature in glass formers and for the first time, in purely alkane chains above their crystallization temperature. We thus have probed collective elastic effects contained not only in the isotropic phase of SCLCPs, but also more generically in the liquid state of ordinary melts and of ordinary liquids

Tracking the Heavy Metal Contaminants Entrained with the Flow into a Trickle Bed Hydrotreating Reactor Packed with Different Catalyst Shapes using Newly Developed Noninvasive Dynamic Radioactive Particle Tracking

A newly developed modified Dynamic Radioactive Particle Tracking system (DRPT) was used to investigate the heavy metal contaminants deposition locations in different catalyst beds, sphere, cylinder, trilobe, and quadrilobed in Trickle Bed Reactors. In the present paper, Kernel Density Estimator (KDE) was used to estimate the probability density distributions of heavy metal contaminants depositions in terms of bed radius height. The result shows that the four cases have similar probability density distribution in terms of radius, while the spherical catalyst has the larger distribution range in terms of bed height. The heavy metal deposition is directly related to the pressure drops along the bed height which indicate the bed porosity and intricate bed structure in catalyst packed beds. Heavy metals have more chance to deposit at higher levels of packed beds with higher pressure drops

Co-sputtered PtMnSb thin films and PtMnSb/Pt bilayers for spin-orbit torque investigations

The manipulation of the magnetization by spin-orbit torques (SOTs) has recently been extensively studied due to its potential for efficiently writing information in magnetic memories. Particular attention is paid to non-centrosymmetric systems with space inversion asymmetry, where SOTs emerge even in single-layer materials. The half-metallic half-Heusler PtMnSb is an interesting candidate for studies of this intrinsic SOT. Here, we report on the growth and epitaxial properties of PtMnSb thin films and PtMnSb/Pt bilayers deposited on MgO(001) substrates by dc magnetron co-sputtering at high temperature in ultra-high vacuum. The film properties were investigated by X-ray diffraction, X-ray reflectivity, atomic force microscopy, and electron microscopy. Thin PtMnSb films present a monocrystalline C1b phase with (001) orientation, coexisting at increasing thickness with a polycrystalline phase with (111) texture. Films thinner than about 5 nm grow in islands, whereas thicker films grow ultimately layer-by-layer, forming a perfect MgO/PtMnSb interface. The thin PtMnSb/Pt bilayers also show island growth and a defective transition zone, while thicker films grow layer-by-layer and Pt grows epitaxially on the half-Heusler compound without significant interdiffusion. (C) 2017 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim</p

All-optical switching in granular ferromagnets caused by magnetic circular dichroism

Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength

Magnetisation switching of FePt nanoparticle recording medium by femtosecond laser pulses

Manipulation of magnetisation with ultrashort laser pulses is promising for information storage device applications. The dynamics of the magnetisation response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage are FePt nanoparticles, for which switching of the magnetisation with optical angular momentum was demonstrated recently. The mechanism remained unclear. Here we investigate experimentally and theoretically the all-optical switching of FePt nanoparticles. We show that the magnetisation switching is a stochastic process. We develop a complete multiscale model which allows us to optimize the number of laser shots needed to switch the magnetisation of high anisotropy FePt nanoparticles in our experiments. We conclude that only angular momentum induced optically by the inverse Faraday effect will provide switching with one single femtosecond laser pulse.EC under Contract No. 281043, FemtoSpin. The work at Greifswald University was supported by the German research foundation (DFG), projects MU MU 1780/8-1, MU 1780/10-1. Research at Göttingen University was supported via SFB 1073, Projects A2 and B1. Research at Uppsala University was supported by the Swedish Research Council (VR), the Röntgen-Ångström Cluster, the Knut and Alice Wallenberg Foundation (Contract No. 2015.0060), and Swedish National Infrastructure for Computing (SNIC). Research at Kiel University was supported by the DFG, projects MC 9/9-2, MC 9/10-2. P.N. acknowledges support from EU Horizon 2020 Framework Programme for Research and Innovation (2014-2020) under Grant Agreement No. 686056, NOVAMAG. The work in Konstanz was supported via the Center for Applied Photonics

Beyond a phenomenological description of magnetostriction

We use ultrafast x-ray and electron diffraction to disentangle spin-lattice coupling of granular FePt in the time domain. The reduced dimensionality of single-crystalline FePt nanoparticles leads to strong coupling of magnetic order and a highly anisotropic three-dimensional lattice motion characterized by a- and b-axis expansion and c-axis contraction. The resulting increase of the FePt lattice tetragonality, the key quantity determining the energy barrier between opposite FePt magnetization orientations, persists for tens of picoseconds. These results suggest a novel approach to laser-assisted magnetic switching in future data storage applications.Comment: 12 pages, 4 figure