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The lining of the alveoli is covered by pulmonary surfactant, a complex mixture of surface-active lipids and proteins that enables efficient gas exchange between inhaled air and the circulation. Despite decades of advancements in the study of the pulmonary surfactant, the molecular scale behavior of the surfactant and the inherent role of the number of different lipids and proteins in surfactant behavior are not fully understood. The most important proteins in this complex system are the surfactant proteins SP-B and SP-C. Given this, in this work we performed non-equilibrium all-atom molecular dynamics simulations to study the interplay of SP-B and SP-C with multi-component lipid monolayers mimicking the pulmonary surfactant in composition. The simulations were complemented byz-scan fluorescence correlation spectroscopy and atomic force microscopy measurements. Our state-of-the-art simulation model reproduces experimental pressure–area isotherms and lateral diffusion coefficients. In agreement with previous research, the inclusion of either SP-B and SP-C increases surface pressure, and our simulations provide a molecular scale explanation for this effect: The proteins display preferential lipid interactions with phosphatidylglycerol, they reside predominantly in the lipid acyl chain region, and they partition into the liquid expanded phase or even induce it in an otherwise packed monolayer. The latter effect is also visible in our atomic force microscopy images. The research done contributes to a better understanding of the roles of specific lipids and proteins in surfactant function, thus helping to develop better synthetic products for surfactant replacement therapy used in the treatment of many fatal lung-related injuries and diseases.

In this article, we present the behavior of two‐mode phase field crystal (2MPFC) method under a concentration dependent deformation. A mixed finite element formulation is proposed for the 2MPFC method that solves a 10th‐order parabolic equation. Lithium concentration diffusion in the electrode particle is captured by the Cahn–Hilliard (CH) equation and the host electrode material, Li$_{x}$Mn$_{2}$O$_{4}$ (LMO), which has a face‐centered cubic (fcc) lattice structure, is modeled using 2MPFC. The coupling between 2MPFC and CH models brings about the concentration dependent deformation in the polycrystalline LMO electrode particle. The atomistic dynamics is assumed to operate on a faster time‐scale compared to the diffusion of lithium, thereby both the 2MPFC and CH models evolve on two different time‐scales. The coupled 2MPFC–CH system models the diffusion induced grain boundary migration in LMO capturing the charging and discharging state of the battery.

Membranes with curvature inducing inclusions display a range of cooperative phenomena, which can be linked to biomembrane function, e.g. membrane tubulation, vesiculation, softening and spontaneous tension. We investigate how these phenomena are related for a fluctuating, framed membrane through analysis of a descretized membrane model by Monte Carlo simulation techniques. The membrane model is based on a dynamically triangulated surface equipped with non-interacting, up-down symmetry breaking inclusions where only terms coupled linearly to mean-curvature are maintained. We show that the lateral configurational entropy plays a key role for the mechanical properties of the semi-flexible membrane, e.g. a pronounced softening at intermediate inclusion coverages of the membrane and generation of membrane tension. Tensionless framed membranes will remain quasi-flat up to some threshold coverage, where a shape instability occurs with formation of pearling or tubular membranes, which below full coverage is associated with segregation of inclusions between the curved and flat membrane geometries. For inclusions with preference for highly curved membranes the instability appears at dilute inclusion coverages and is accompanied by strong configurational fluctuations.

We have studied the effect of replacing Mn3+ by Cr3+ on the structure, transport and magnetism in the bilayered manganite LaSr2Mn2O7. Although no structural transition was observed in LaSr2Mn2 yCryO7 (0.1

Spin coating is one of the most versatile methods to generate nanostructured block copolymer (BCP) thin films which are highly desired for many applications such as nanolithography or organic electronics. The self-assembly pathways through phase separation, both in solvent and in bulk, strongly influence the final BCP structure obtained after spin coating. As a demonstration, the formation of highly ordered in-plane lamellae is elucidated herein by using in situ grazing incidence small-angle X-ray scattering. A key step in this complex fast organization process is the formation of intermediate micellar phases triggered by solvent affinity toward one of the block. Indeed, directional coalescence of a short-lived intermediate hexagonal structure of cylindrical micelles enables the development of a final highly ordered lamellar structure, predominantly oriented parallel to the substrate surface. These results suggest that the existence of such transient micellar phases is a crucial process in order to produce highly ordered structures with a specific orientation directly after the BCP thin film deposition; and should be the focus of further optimization for the directed self-assembly and, more generally, in the bottom-up nanostructure fabrication.

Amyloid deposits of aggregated beta-amyloid Aβ(1-42) peptides are a pathological hallmark of Alzheimer's disease. Aβ(1-42) aggregates are known to induce biophysical alterations in cells, including disruption of plasma membranes. We investigated the microviscosity of plasma membranes upon interaction with oligomeric and fibrillar forms of Aβ(1-42). Viscosity-sensing fluorophores termed molecular rotors were utilised to directly measure the microviscosities of giant plasma membrane vesicles (GPMVs) and plasma membranes of live SH-SY5Y and HeLa cells. The fluorescence lifetimes of membrane-inserting BODIPY-based molecular rotors revealed a decrease in bilayer microviscosity upon incubation with Aβ(1-42) oligomers, while fibrillar Aβ(1-42) did not significantly affect the microviscosity of the bilayer. In addition, we demonstrate that the neuroprotective peptide H3 counteracts the microviscosity change induced by Aβ(1-42) oligomers, suggesting the utility of H3 as a neuroprotective therapeutic agent in neurodegenerative disorders and indicating that ligand-induced membrane stabilisation may be a possible mechanism of neuroprotection during neurodegenerative disorders such as Alzheimer's disease.

This article describes the preparation of porous poly (¿-caprolactone), PCL, membranes by supercritical CO2 (SCCO2) foaming, displaying surface hierarchical macroporosity which could be tailored by careful control of the pressure, in the range of 150¿250 bar, and depressurization processes in several steps, showing also pore interconnectivity between both membrane faces. The membranes exhibited two distinct types of surface macroporosity, the larger with diameter sizes of 300¿500 ¿m were surrounded by and also composed of smaller pores of 15¿50 ¿m (same size as inner pores). Membranes were prepared by solvent casting and submitted to different SCCO2 foaming. Parameters such as membrane thickness, CO2 flow, foaming time, pressure, temperature and the depressurization processes (rate and profiles), were varied to determine their influence on final porosity and to decipher which parameters were the most critical ones in terms of surface hierarchical pore organization. No remarkable changes in PCL crystallinity were found when membranes were processed under SCCO2. Finally, biological evaluation of the porous membranes was achieved by seeding human skin fibroblasts on the prepared membranes. The results, in terms of cell adhesion, spreading, proliferation and metabolic activity indicate that these membranes could hold promise for the fabrication of meshes with controlled porosity for tissue engineering applications.

Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion.

International audience; A high purity Fe15Cr alloy has been irradiated with 1 MeV electrons at 573 K to doses up to 0.7 dpa. Alpha' precipitates have been revealed by Atom Probe Tomography (APT). They were not associated with the irradiation induced defects confirming a radiation-enhanced mechanism. Comparison with literature shows that alpha' precipitation occurred after similar doses after neutron and electron irradiations but not under ion irradiation. Electron irradiation is more efficient to enhance alpha' precipitation. The same a Cr solubility limit as under neutron irradiation were found. alpha' Cr equilibrium composition at 573 K has been measured for the first time with APT.

We consider the one-band Hubbard model on the square lattice by using variational and Green's function Monte Carlo methods, where the variational states contain Jastrow and backflow correlations on top of an uncorrelated wave function that includes BCS pairing and magnetic order. At half filling, where the ground state is antiferromagnetically ordered for any value of the on-site interaction $U$, we can identify a hidden critical point $U_{\rm Mott}$, above which a finite BCS pairing is stabilized in the wave function. The existence of this point is reminiscent of the Mott transition in the paramagnetic sector and determines a separation between a Slater insulator (at small values of $U$), where magnetism induces a potential energy gain, and a Mott insulator (at large values of $U$), where magnetic correlations drive a kinetic energy gain. Most importantly, the existence of $U_{\rm Mott}$ has crucial consequences when doping the system: We observe a tendency to phase separation into a hole-rich and a hole-poor region only when doping the Slater insulator, while the system is uniform by doping the Mott insulator. Superconducting correlations are clearly observed above $U_{\rm Mott}$, leading to the characteristic dome structure in doping. Furthermore, we show that the energy gain due to the presence of a finite BCS pairing above $U_{\rm Mott}$ shifts from the potential to the kinetic sector by increasing the value of the Coulomb repulsion., Comment: 10 pages, 7 figures

A method using fast hot pressing to join half-Heusler (HH) thermoelectric materials directly to an electrical current collector (Ag electrode) without using a third filler material is introduced. The compositions of the HH alloys used are Hf0.5Zr0.5CoSn0.2Sb0.8 and Ti0.6Hf0.4NiSn for p- and n-type, respectively. Using this method, the quality of the HH-electrode contacts is improved due to their low electrical contact resistance and less reaction-diffusion layer. The microstructure and chemical composition of the joints were examined using a scanning electron microscope equipped with energy-dispersive x-ray analysis. The electrical characteristics of the interfaces at the contacts were studied based on electrical contact resistance and Seebeck scanning microprobe measurements. In this paper, we show that joining the HH to a Ag electrode directly using fast hot pressing resulted in lower contact resistance and better performance compared with the method of using active brazing filler alloy.

We investigate a series of manganese oxides, the La0.225Pr0.4(Ca1−xSrx)0.375MnO3 system. The x=0 sample is a prototype compound for the study of phase separation in manganites, where ferromagnetic and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+ gradually turns the system into a homogeneous ferromagnet. Our results show that the material structure plays a major role in the observed magnetic properties. On cooling, at temperatures below ∼100 K, a strong contraction of the lattice is followed by an increase in the magnetization. This is observed both through thermal expansion and magnetostriction measurements, providing distinct evidence of magneto-elastic coupling in these phase separated compounds. Fil: Eslava, G.G.. Universidade Federal do Rio de Janeiro; Brasil Fil: Parisi, F.. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Bernardo, P.L.. Universidade Federal do Rio de Janeiro; Brasil Fil: Quintero, Mariano Horacio. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Leyva, G.. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Cohen, L.F.. Imperial College. Theoretical Physics Group. Blackett Laboratory; Reino Unido Fil: Ghivelder, L.. Universidade Federal do Rio de Janeiro; Brasil

We have studied the effect of substituting copper at the manganese site on the structure, resistivity and magnetism of the bilayer manganite LaSr2Mn2-xCuxO7 (0

We report the effect of Si doping on the magnetization and transport behavior in CeFe2. It is found that Si doping is able to stabilize the low temperature antiferromagnetic state in CeFe2, resulting in a first order ferromagnetic to antiferromagnetic transition. The strong magnetostructural coupling in this system is found to give rise to martensitic features, which manifest in the magnetization and transport data. We show clear evidence of this influence through the multi-step magnetization behavior, unusual relaxation effect, thermal and magnetic history dependencies. The non-equilibrium magnetic state at low temperatures is also revealed by the fact that the magnetization steps can be induced with the help of an appropriate measurement protocol. Detailed magnetization relaxation studies have been carried out to understand the dynamics of magnetic phase transition. Martensitic scenario is also found to cause multi-step behavior in the magnetoresistance isotherms. By compiling all the distinct features in this system with those of other related systems, we conclude that this can be a model system that may contribute to understand the rich physics of phase separation and the martensitic scenario, both theoretically and experimentally.

The official published version of the Article can be accessed from the link below - Copyright @ 2009 The Minerals, Metals & Materials Society and ASM International The growing importance of Al-Sn based alloys as materials for engineering applications necessitates the development of uniform microstructures with improved performance. Guided by the recently thermodynamically assessed Al-Sn-Cu system, two model immiscible alloys, Al-45Sn-10Cu and Al-20Sn-10Cu, were selected to investigate the effects of intensive melt shearing provided by the novel melt conditioning by advanced shear technology (MCAST) unit on the uniform dispersion of the soft Sn phase in a hard Al matrix. Our experimental results have confirmed that intensive melt shearing is an effective way to achieve fine and uniform dispersion of the soft phase without macro-demixing, and that such dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm and 60 seconds will be adequate to produce fine and uniform dispersion of the Sn phase, and that higher shearing speed and prolonged shearing time can only achieve minor further refinement. This work is funded by the EPSRC and DTI

We report extended X-ray absorption fine structure measurements at the Mn K edge on (La0.63Ca037) (Mn0.92Cu0.08)O-3 and (La0.25Ca075)(Mn0.92Cu0.08)O-3 samples. We observe that the Cu2+ substitution in these two compounds belonging from the opposite sides of the phase diagram induces two very different effects. In the first case, it weakens ferromagnetic ordering, while in the second one, it does not significantly modify the charge ordering present in the system.

International audience; Different synthesis routes have been implemented to prepare macroporous monoliths with vinyl pendant groups and micrometric skeletons and through-pore sizes. A standard process combining the synthesis of a widely used (methyl-trimethoxysilane/tetramethoxysilane) (MTMS/TMOS) hybrid silica monolith and the postsilanization with vinyltrimethoxysilane (VTMS) was used as reference material (Vgr-MTMS). An alternative "one-pot" procedure was used to obtain vinylized hybrid monoliths. Two VTMS/TMOS hybrid based monoliths were successfully prepared starting from 20% (w) and 80% (w/w) of VTMS, respectively, called 20-VTMS and 80-VTMS. Monoliths were characterized by SEM, nitrogen-adsorption isotherm, and Si-29 MAS NMR spectroscopy. One-pot synthesis allowed to obtain higher vinyl contents (15.9 and 61.5 mol % of Si atoms bonded to vinyl groups respectively for 20-VTMS and 80-VTMS) than for the postgrafted one (7.1%). Accessibility of vinyl groups was determined by the extent of bromination reactions followed by FTIR-ATR spectroscopy. Bromination with reaction yields were higher than 80% for all materials (80%, 85%, and 100% for 80-VTMS, 20-VTMS, and Vgr-MTMS respectively), with no diffusion issues The chemical reactivity of the pendant vinyl groups was investigated through radical-mediated thiol-ene reaction and radical-initiated bisulfite addition. Reaction yields for the two VTMS hybrid monoliths were quite lower (4-6%) than those obtained (about 50%) for the Vgr-MTMS monolith. The difference in reactivity was attributed to the steric hindrance of the vinyl moieties at the surface of hybrid materials. However, the lower reactivity of vinyl groups is compensated by their considerably higher surface density. Thus, hybrid monoliths are advantageous over their grafted counterparts, due to their higher hydrolytic stability and to the greater simplicity of the one-pot process. A chromatographic application exemplifies their interest and performances in separation science.

Cavitation in a liquid moving past a constraint is numerically investigated by means of a free-energy lattice Boltzmann simulation based on the van der Waals equation of state. The fluid is streamed past an obstacle, and depending on the pressure drop between inlet and outlet, vapor formation underneath the corner of the sack-wall is observed. The circumstances of cavitation formation are investigated and it is found that the local bulk pressure and mean stress are insufficient to explain the phenomenon. Results obtained in this study strongly suggest that the viscous stress, interfacial contributions to the local pressure, and the Laplace pressure are relevant to the opening of a vapor cavity. This can be described by a generalization of Joseph's criterion that includes these contributions. A macroscopic investigation measuring mass flow rate behavior and discharge coefficient was also performed. As theoretically predicted, mass flow rate increases linearly with the square root of the pressure drop. However, when cavitation occurs, the mass flow growth rate is reduced and eventually it collapses into a choked flow state. In the cavitating regime, as theoretically predicted and experimentally verified, the discharge coefficient grows with the Nurick cavitation number. (C) 2015 AIP Publishing LLC.

Dislocations are one-dimensional topological defects that occur frequently in functional thin film materials and that are known to degrade the performance of InxGa1-xN-based optoelectronic devices. Here, we show that large local deviations in alloy composition and atomic structure are expected to occur in and around dislocation cores in InxGa1-xN alloy thin films. We present energy-dispersive X-ray spectroscopy data supporting this result. The methods presented here are also widely applicable for predicting composition fluctuations associated with strain fields in other inorganic functional material thin films.

For applications where droplet breakup and surfactant adsorption are strongly coupled, a diffuse interface model is developed. The model is based on a free energy functional, partly adapted from the sharp interface model of [Diamant and Andelman 34(8):575–580, (1996)]. The model is implemented as a 2D Lattice Boltzmann scheme, similar to existing microemulsion models, which are coupled to hydrodynamics. Contrary to these microemulsion models, we can describe realistic adsorption isotherms, such as the Langmuir isotherm. From the free energy, functional analytical expressions of equilibrium properties are derived, which compare reasonably with numerical results. Interfacial tension lowering scales with the logarithm of the area fraction of the interface unloaded with a surfactant: $$\Delta \sigma \sim \ln(1-\psi_0)$$ . Furthermore, we show that adsorption kinetics are close to the classical relations of Ward and Tordai. Prelimary simulations of droplets in shear flow show promising results, with surfactants migrating to interfacial regions with highest curvature. We conclude that our diffuse interface model is very promising for apprehending the above-mentioned applications as membrane emulsification.

Photochemical switching has been studied of double-tailed phosphate amphiphiles containing azobenzene units in both tails in aqueous vesicular dispersions and in mixed vesicular systems with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Since the ease of switching depends on the strength of the bilayer packing, particular emphasis has been placed on the occurrence of H-aggregation in the hydrophobic core of the vesicles. UV-vis spectrometry was employed to monitor H-aggregation and showed how this process depends on the ionic strength and on the mode of preparation of the vesicles. Two types of H-aggregates were observed in mixed DOPC vesicles with 5 mol % of azobenzene phosphate: one with lambda(max) at around 300 nm and one with lambda(max) at 305-320 nm. Those with lambda(max) at 300 nm could not be trans-cis photoisomerized, whereas those with lambda(max) at 305-320 nm are more loosely packed and can be photochemically switched. The permeability of the vesicular bilayers, as probed with leakage experiments using calcein as a fluorescent probe, was examined as another measure for the strength of bilayer packing. Leakage occurred only for DOPC vesicles containing more than 20 mol % of azobenzenephosphate, irradiated with UV light to induce trans-cis photoisomerization. We contend that detailed information on bilayer packing will be of crucial importance for fine-tuning the lateral pressure in vesicular membranes with the ultimate aim to steer the opening and closing of mechanosensitive protein channels of large conductance.

In silicon nanocluster (Si-NC) memories, Si-NC embedded in the gate oxide of an MOSFET are used to store and release electrons thereby modifying the threshold of the transistor. This paper describes the formation of its core functional structure, the Si-NC MOS memory capacitor, by annealing a SiO2/SiOx (x

In the late stage dynamics of systems evolving via domain coarsening, the linear response function splits into the sum of a stationary term, due to thermal fluctuations within domains, and of an aging term due to off-equilibrium interface dynamics. The latter contribution is analyzed in the pure Ising model under variation of space dimensionality and in the random field Ising model in one dimension. The variety of behaviors observed can be accounted for in terms of the effective response associated to a single interface. Implications for the connection between static and dynamic properties are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

We analyze the interplay between charge ordering, magnetic ordering, and the tendency toward phase separation and its importance for the physics of manganites. A simple model of charge ordering is considered. It takes into account both the Coulomb repulsion at neighboring sites responsible for charge ordering and the essential magnetic interactions. It is shown explicitly that at any deviation from half-filling (n≠1/2) the system is unstable with respect to phase separation into charge-ordered regions with n=1/2 and metallic regions with smaller electron or hole density. A possible structure of this phase-separated state (metallic droplets in a charge-ordered matrix) is discussed. We construct the phase diagram reproducing the main features observed in real manganites. Based on the same physical picture, we also derive explicit expressions for the dc conductivity and noise power in the phase-separated state. It is shown that the noise spectrum has a nearly 1/f form in the low-frequency range.

We discuss novel simulation methods for 3D pattern formation in complex amphiphilic systems. The focus is on the supra-molecular or mesoscopic level. The building blocks consist of sequences of dissimilar monomers. connected in copolymer chain molecules. Internal factors such as composition and architecture of the polymers. but also external factors such as applied shear. embedded reactions and level of confinement control the self-organization phenomena. Specific examples include dynamical pattern formation in polymer surfactant solution, reactive polymer blends and surface directed structure formation in block copolymer liquids. The approach lives in a twilight zone between scientific disciplines. The ambitious goal is the invention of methods For the rational design of truly complex bio-mimicking materials, in which we combine principles from chemical engineering, physics, chemistry and biology. The keyword is self-organization. of course. But do not be mistaken: autonomous self-organization leads to trouble, modulated self-organization leads to beauty.

Cataloged from PDF version of article. Active Brownian particles are capable of taking up energy from their environment and converting it into directed motion; examples range from chemotactic cells and bacteria to artificial micro-swimmers. We have recently demonstrated that Janus particles, i.e. gold-capped colloidal spheres, suspended in a critical binary liquid mixture perform active Brownian motion when illuminated by light. In this paper, we investigate in more detail their swimming mechanism, leading to active Brownian motion. We show that the illumination-borne heating induces a local asymmetric demixing of the binary mixture, generating a spatial chemical concentration gradient which is responsible for the particle’s self-diffusiophoretic motion. We study this effect as a function of the functionalization of the gold cap, the particle size and the illumination intensity: the functionalization determines what component of the binary mixture is preferentially adsorbed at the cap and the swimming direction (towards or away from the cap); the particle size determines the rotational diffusion and, therefore, the random reorientation of the particle; and the intensity tunes the strength of the heating and, therefore, of the motion. Finally, we harness this dependence of the swimming strength on the illumination intensity to investigate the behavior of a micro-swimmer in a spatial light gradient, where its swimming properties are space-dependent.

Through extensive state-of-the-art numerical simulations, we study the behavior of the dipolar hard sphere model at low temperatures and low densities, shedding light on a region of the phase diagram where a topological phase transition has long been thought to occur. We show that the system exhibits remarkable and unusual behaviors, like a very low density percolation locus and a stabilization of rings over chain structures. This unexpected abundance of rings comes from a delicate balance between the lower ring energy and the end-to-end chain entropy, and hints at a possible mechanism for the suppression of the gas-liquid phase separation. Our results open the possibility for refined theoretical approaches which, in addition to the previously encompassed chain and branched geometries, must also include the significant contribution arising from ring formation.

We present a confocal-microscopy study of demixing and remixing in binary liquids containing colloidal particles. First, particle-stabilized emulsions have been fabricated by nucleation and growth of droplets upon cooling from the single-fluid phase. We show that their stability mainly derives from interfacial particles; the surplus of colloids in the continuous phase possibly provides additional stability. Upon heating these emulsions, we have observed the formation of polyhedral cellular networks of colloids, just before the system remixes. Given a suitable liquid-liquid composition, the initial emulsions cross the binary-liquid symmetry line due to creaming. Therefore, upon heating, the droplets do not shrink and they remain closely packed. The subsequent network formation relies on a delicate balance between the Laplace pressure and the pressure due to creaming/remixing. As high concentrations of colloids in the cell walls inhibit film thinning and rupture, the networks can be stabilized for more than 30 minutes. This opens up an avenue for their application in the fabrication of advanced materials., http://dx.doi.org/10.1039/b918002h

We present a numerical study of the random Blume-Capel model in three dimension. The phase diagram is characterized by spin-glass/paramagnet phase transitions both of first and second order in the thermodynamic sense. Numerical simulations are performed using the Exchange-Monte Carlo algorithm, providing clear evidence for inverse freezing. The main features at criticality and in the phase coexistence region are investigated. We are not privy to other 3D short-range systems with quenched disorder undergoing inverse freezing., 4 pages, 3 figures

Natural surfaces are often structured with nanometre-scale domains, yet a framework providing a quantitative understanding of how nanostructure affects interfacial energy, italic gammaSL, is lacking. Conventional continuum thermodynamics treats italic gammaSL solely as a function of average composition, ignoring structure. Here we show that, when a surface has domains commensurate in size with solvent molecules, italic gammaSL is determined not only by its average composition but also by a structural component that causes italic gammaSL to deviate from the continuum prediction by a substantial amount, as much as 20% in our system. By contrasting surfaces coated with either molecular- (5 nm), we find that whereas the latter surfaces have the expected linear dependence of italic gammaSL on surface composition, the former show a markedly different non-monotonic trend. Molecular dynamics simulations show how the organization of the solvent molecules at the interface is controlled by the nanostructured surface, which in turn appreciably modifies italic gammaSL.

We investigate the kinetics of self-assembly by means of Brownian dynamics simulation based on a idealized fluid model ( two 'sticky' spots on a sphere) in which the particles are known to form into dynamic polymer chains at equilibrium. To illustrate the slow evolution of the properties of these self-assembling fluids to their equilibrium assembled state values at long times, we perform Brownian dynamics simulations over a range of quench depths from the high temperature unassembled state to the low temperature assembled state. We investigate the time dependence of the average chain length ( cluster mass), the order parameter for the assembly transition ( fraction of particles in the chain state) and the potential energy of the fluid. The rate constant governing the self-assembly ordering process depends both on kinetic-related factors ( the particle hydrodynamic radius and the fluid viscosity) and on thermodynamic energetic variables governing the self-assembly transition (i.e., the entropy and enthalpy of assembly). We provide evidence that an essentially parameter-free description of the polymerization kinetics can be formulated for this model.

We report on structural, magnetic, and transport properties of La0.7Ba0.3MnO3 thin films, epitaxially grown on MgO substrates. Despite the quite similar structural features if compared to crystalline manganite films, our samples show a metal-insulator transition temperature of about 200 K, sizeably lower than the bulk-value (T-MI similar or equal to 345 K). Moreover, the magnetotransport properties show the absence of saturation in the magnetoresistance and localization phenomena at low temperatures (T < 30 K). The temperature behavior of the magnetization shows a Curie temperature T-c value above room temperature, ruling out effects due to oxygen deficiency. All these findings are analyzed in terms of possible physical mechanisms related to the growth in the presence of large mismatch between film and substrate lattice parameters. (c) 2008 American Institute of Physics.

Recent experiments on imbalanced fermion gases have proved the existence of a sharp interface between a superfluid and a normal phase. We show that, at the lowest experimental temperatures, a temperature difference between N and SF phase can appear as a consequence of the blocking of energy transfer across the interface. Such blocking is a consequence of the existence of a SF gap, which causes low-energy normal particles to be reflected from the N-SF interface. Our quantitative analysis is based on the Hartree-Fock-Bogoliubov-de Gennes formalism, which allows us to give analytical expressions for the thermodynamic properties and characterize the possible interface scattering regimes, including the case of unequal masses. Our central result is that the thermal conductivity is exponentially small at the lowest experimental temperatures., Comment: 11 pages, 5 figures

Thin films of La0.7Sr0.3MnO3 were grown by molecular beam epitaxy on (001)LaAlO3 crystals. High resolution X-ray diffraction analysis proves the presence of twins in the films at room temperature, showing that the twin structure of the substrate which forms at the Pm (3) over barm -> R (3) over barc ferroelastic transition at T-F = 813 K served as a template for the film microstructure. Magnetic measurements indicate a thermomagnetic irreversibility which is ascribed to the quenched disorder related to twinning and discussed in terms of coexisting ferromagnetic and spin disordered regions connected with the undeformed domain cores and strained domain walls respectively.

We analyze the Blume-Emery-Griffiths model with disordered magnetic interaction displaying the inverse freezing phenomenon. The behaviour of this spin-1 model in crystal field is studied throughout the phase diagram and the transition and spinodal lines for the model are computed using the Full Replica Symmetry Breaking Ansatz that always yelds a thermodynamically stable phase. We compare the results both with the quenched disordered model with Ising spins on lattice gas - where no reentrance takes place - and with the model with generalized spin variables recently introduced by Schupper and Shnerb [Phys. Rev. Lett. 93, 037202 (2004)]. The simplest version of all these models, known as Ghatak-Sherrington model, turns out to hold all the general features characterizing an inverse transition to an amorphous phase, including the right thermodynamic behavior., Comment: 6 pages, 4 figures, to appear in the Proceeding for the X International Workshop on Disordered Systems (2006), Molveno, Italy

We have systematically studied the transport properties of colossal magnetoresistance (CMR) manganite films at temperatures of up to $550\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ by changing parameters influencing the amount of disorder in the system. Independent of the type and amount of disorder, the resistivity can always be described using a ${T}^{\ensuremath{\alpha}}$-power law in the ferromagnetic-metallic phase and a thermally activated behavior in the polaronic-insulating phase. A linear correlation between both the value of the $\ensuremath{\alpha}$ coefficient and the polaron formation energies ${E}_{g}$ as a function of the metal-insulator transition temperature ${T}_{\mathit{MI}}$ has been found. Our results indicate the possibility of describing the transport properties in CMR manganites in terms of a single disorder parameter.

In the mid-infrared absorption of Sr{1-x}Ce{x}MnO{3} at low electron doping (x = 0.05), a band at 0.3 eV is fully replaced by another one at 0.9 eV as the system becomes antiferromagnetic (AF) of type $G$. A weaker effect occurs at x = 0.10 for an AF phase of type $C$. One thus directly measures the electron hopping energies for spin parallel and anti-parallel to that of the host ion. The Hund's, crystal-field, and Jahn-Teller splittings for the Mn{3+} ions in a Mn{4+} matrix, can also be derived., Comment: Includes 8 Postscript figures

Polymeric gel electrolytes, based on a blend of poly(methylmethacrylate)/poly(vinylidene fluoride) (PMMA/PVdF), ethylene carbonate/propylene carbonate (EC/PC) as plasticizer and lithium Perchlorate as electrolyte, have been studied as a function of the different polymeric ratios to obtain the best compromise between ionic conduction and mechanical properties of the systems involved. Ionic conductivity and the lithium self-diffusion coefficient were measured by the PFG-NMR method, which revealed a maximum of lithium mobility for the composition PMMA 60%-PVdF 40%. The Raman spectroscopic study revealed a change of the interaction between that of the lithium cations and the plasticizer molecules for different PMMA/PVdF ratios. Oscillatory rheological tests have shown better mechanical properties for the intermediate compositions of the blend. (c) 2006 Elsevier B.V. All rights reserved.

The interaction between two disks immersed in a 2D nematic is investigated (i) analitically using the tensor order parameter formalism for the nematic configuration around isolated disks and (ii) numerically using finite element methods with adaptive meshing to minimize the corresponding Landau-de Gennes free energy. For strong homeotropic anchoring, each disk generates a pair of defects with one-half topological charge responsible for the 2D quadrupolar interaction between the disks at large distances. At short distance, the position of the defects may change, leading to unexpected complex interactions with the quadrupolar repulsive interactions becoming attractive. This short range attraction in all directions is still anisotropic. As the distance between the disks decreases their preferred relative orientation with respect to the far-field nematic director changes from oblique to perpendicular., Comment: 7 pages, 7 figures

We investigate the combined influence of superexchange and electron-phonon interactions on the excitation spectra and on hole propagation in a ferromagnetic plane of LaMnO 3 . The Jahn-Teller effect modifies the energies of both orbital and phonon excitations and can lead to modes with mixed character, and for strong Jahn-Teller interaction even to a structural instability due to profound softening of one of the phonon modes. Solving the problem of hole propagation in the self-consistent Born approximation, we found that the quasiparticle states at the bottom of the spectrum are accompanied by broad structures, representing vibrational side bands which result from the hole-lattice coupling.

We show that depletion forces induced by surfactant micelles can be profitably exploited to perform an efficient a posteriori size fractionation of suspensions of optically anisotropic colloids. Efficiency and limits of the fractionation protocol are discussed both on 'model' and technical polydisperse lattices. This method can be used to single out fractions composed by long fibrillar particles, showing evidence of mesogenic behaviour. Depolarized dynamic light scattering is used to extract the particle translational and rotational diffusion coefficients DT and DR as a function of particle volume fraction. Both the concentration behaviour of DT and the full shape of the depolarized correlation functions show distinctive and partially unexpected features.

The magnetic and transport properties of the manganites with the perovskite structure are mainly characterized by a competition between ferromagnetism and antiferromagnetism, and between a metallic like and an insulating behavior. Charge and orbital ordering, and phase separation play a prominent role in the appearance of such properties, since they can be modified in a spectacular manner by external factors, making the different physical properties metastable. There we describe two effects that deeply modify those properties, the doping of Mn sites and the thermal cycling under a magnetic field. The doping of Mn sites by various magnetic cations-Cr, Co, Ni, Ru, Rh, Ir-destroys charge/orbital-ordering and induces ferromagnetism and metallicity in the antiferromagnetic matrix of the manganites. The magnetic phase diagram of the systems Ln(1-x)Ca(x)MnO(3) is considerably modified by such doping. The metastability of the magnetic states is explained in terms of models based on the electronic structure of the doping elements in connection with a possible valence fluctuation. The thermal cycling is also a spectacular effect, observed in chromium doped manganites. For instance, an increase of resistivity by several orders of magnitude can be observed by thermal cycling under a magnetic field, whereas no effect is obtained in the corresponding undoped material. This behavior is interpreted in terms of strains induced charge localization, at the interface between ferromagnetic/antiferromagnetic domains in the antiferromagnetic matrix. (C) 2002 Elsevier Science Ltd. All rights reserved.

The effect of partial 16 O→ 18 O isotope substitution on electrical and thermal resistivity and AC magnetic susceptibility was studied for (La 0.25 Pr 0.75 ) 0.7 Ca 0.3 MnO 3 ceramic samples. The measurements were performed for 11 samples with the molar percentage of 18 O varying from zero to 90%. For 0–40% enrichment by 18 O, the low-temperature resistivity had a metallic behavior. At higher 18 O content, the samples exhibited a percolation-like transition to the insulating state. Magnetic measurements demonstrated that the behavior typical of antiferromagnets arose only at 18 O enrichment exceeding 60%, whereas at lower 18 O content, we obtain an appreciable ferromagnetic contribution. The experimental data are interpreted in the picture of a percolation-type phase-separated system with the regions of ferromagnetic metal and antiferromagnetic charge ordered insulator.

A thorough numerical investigation of the slow dynamics in the d=1 random field Ising model in the limit of an infinite ferromagnetic coupling is presented. Crossovers from the preasymptotic pure regime to the asymptotic Sinai regime are investigated for the average domain size, the autocorrelation function and staggered magnetization. By switching on an additional small random field at the time tw the linear off equilibrium response function is obtained, which displays as well the crossover from the nontrivial behavior of the d=1 pure Ising model to the asymptotic behavior where it vanishes identically., Comment: 12 pages, 10 figures

We argue that elastic interactions between ions in different valence states can play an essential role in stabilization of stripes(or 2D "sheets")in doped oxides. These interactions are in general long-range and anisotropic (attractive in certain directions and repulsive in others). This can naturally give rise to stripe-like structures in insulating materials. We illustrate this general idea with certain specific examples and show that the situation can be described by the Ising model with anisotropic interactions. The case of anisotropic impurities, relevant e.g. for manganites, is also briefly discussed., Comment: 4 pages, RevTex, accepted for publication in Europhysics Letters

Here we report direct evidence for charge ordering in the oxygen doped La 2 CuO 4.1 superconductor by x-ray diffraction using a third generation synchrotron source. We observe 1D charge ordering and oxygen ordering in an optimally doped superconductor (T c =40K) well beyond the phase separation regime. The order parameter of the anharmonic 1D CDW shows a critical behavior (T co -T) 0.5 T co =190K. The oxygen ordering and the polaron 1D CDW with its associated orbital wave, realize a superlattice of quantum stripes with a wavevector that at the density of charge carriers, r s ∼6, in the superconducting stripes satifies the shape resonance condition for T c amplification.

We argue that in lightly hole doped perovskite-type Mn oxides the holes (Mn$^{4+}$ sites) are surrounded by nearest neighbor Mn$^{3+}$ sites in which the occupied $3d$ orbitals have their lobes directed towards the central hole (Mn$^{4+}$) site and with spins coupled ferromagnetically to the central spin. This composite object, which can be viewed as a combined orbital-spin-lattice polaron, is accompanied by the breathing type (Mn$^{4+}$) and Jahn-Teller type (Mn$^{3+}$) local lattice distortions. We present calculations which indicate that for certain doping levels these orbital polarons may crystallize into a charge and orbitally ordered ferromagnetic insulating state., Comment: 5 pages, 4 figures, to be published in PRB

Magnetization (M), Magnetocaloric effect (MCE), and Magnetoresistance (MR) in Co substituted La0.67Sr0.33Mn1-xCoxO3 (x = 0.03, 0.05, and 0.1) samples have been investigated. All the studied samples were crystallized into a single phase rhombohedral structure with R (3) over barc space group. The Curie temperature (T-C) is found to decrease with the increase of Co content and for the composition x = 0.1, a cluster glass-like nature is observed. Temperature variation of magnetic entropy change (Delta S-M) shows a positive peak at TC for the composition x = 0.1 with Delta S-M = 3.1 J/kg K and relative cooling power, RCP = 155 J/kg at a magnetic field of 50 kOe. Again, the critical analysis of the paramagnetic to ferromagnetic transition and the scaling behaviour of field dependence of MCE for x = 0.1 composition is also reported. Furthermore, the temperature dependence of electrical resistivity under the magnetic fields up to 50 kOe is reported along with the values of 20% enhancement in MR at room temperature for the Co substituted samples. (C) 2013 AIP Publishing LLC.

We construct a phase diagram for the materials with colossal magnetoresistance. The basic model which describes these materials is a double-exchange model. We rigorously prove that a ground state of this model corresponds to a phase-separated state with small ferromagnetic polarons inside an antiferromagnetic matrix. The general picture of a percolative state, which emerges from our calculations, is in good agreement with recent experiments on doped manganites.

"The crystal and magnetic structure of (La0.50Ca0.50)(Mn1-xBx) O-3 (x = 0.00, 0.03, 0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurements and neutron powder diffraction followed by Rietveld refinement. In the pristine compound an orthorhombic to monoclinic phase transition is detected on cooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising. Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of (La0.50Ca0.50) MnO3, despite the fact that these ions are characterized by different external electronic configurations. After substitution, the orthorhombic to monoclinic phase transition is hindered. As a consequence, charge and orbital orderings are suppressed, as is the superexchange; double exchange takes place inducing ferromagnetic (FM) interactions. No evidence for stable magnetic interaction between Cr3+ or Ni2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples a detectable quantity of monoclinic phase forms during cooling, inside which AFM interactions take place. The amount of this secondary monoclinic phase decreases on increasing Ni substitution; the global FM magnetic moment decreases as well, due to a spin-cluster glass-type state arising. As a result a FM state is found to coexist with a spin-cluster glass-type state."