Dipolar Chains Research Articles

Influence of short range potential on field induced chain aggregation in low density dipolar particles

We investigate, by Monte Carlo simulation, the effect of the steepness of the short range repulsive potential on mesostructure formation in dipolar particles submitted to a strong external field. Columnar clusters made of several dipolar chains are only observed when the short-range potential is sufficiently steep. The confinement of the dipolar liquid in a slit geometry instead of bulk conditions suppresses the formation of columns.

Synthesis and characterization of the conjugated polymers tethered with dipolar side chains containing a benzothiadiazole entity for bulk heterojunction solar cells

New conjugated copolymers (P1−P3) containing dipolar side chains connected to the main chain via triphenylamine donors have been synthesized and characterized. The side chains of these polymers have an electron deficient benzothiadiazole moiety in the spacer, but with different acceptors at the end. By changing the acceptor moieties of the side chain, the absorption spectra and HOMO/LUMO gaps of the polymers can be fine-tuned, ranging from 1.86 to 1.59eV. Solution processed bulk heterojunction (BHJ) solar cells using these polymers as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor were fabricated and measured under 100mWcm−2 of AM 1.5 illumination. The cell based on the blend of P1/PCBM (1:1, w/w) exhibited the highest power conversion efficiency of 1.78%, with open circuit voltage (Voc)=0.79V, short circuit current (Jsc)=6.63mAcm−2 and fill factor (FF)=0.34, respectively.

Nonlinear Resonant Light Scattering by a Diatomic System

Polyatomic systems of two types are considered: a one-dimensional periodic chain of noninteracting dipoles and a plane layer of uniformly and irregularly distributed noninteracting dipoles. It is demonstrated that the Mollow triplet is observed in the spectrum of scattered radiation when the angles of strong field incidence are not very close to π/2. For sliding angles of strong field incidence on the system of dipoles, waves with frequencies of the strong field and high-frequency triplet component are scattered in forward and backward directions. In this case, radiation of low-frequency triplet component propagates along the layer on its bothsides in the form of two nonuniform waves attenuating exponentially with the distance from the layer.

Morphology, Dielectric and Thermal Properties of Poly(sulfobutylbetaine)/Montmorillonite (PMBS‐4/MMT) Nanocomposites as Solid Polymer Electrolytes

AbstractPolymeric electrolyte composites based on polymer poly(sulfobutylbetaines) (PMBS‐4) and 1%, 3% and 5% montmorillonite (MMT) modified with organic ions, dodecyldimethyl(3‐sulfo‐propyl) ammonium hydroxide (C12SB) were synthesized. The structural modification and electrochemical properties of samples were investigated to understand the effects of organic MMT in a polymer matrix on ionic conductivity. The modification of the clay with organic ions resulted in a larger d‐spacing which makes easier the penetration of PMBS‐4 into the interlayer galleries. The values of Tg obtained from differential scanning calorimetry are 18 °C, 20 °C, 20 °C and 27 °C for PMBS‐4, PMBS‐4/C12SB‐MMT 1%, PMBS‐4/C12SB‐MMT 3% and PMBS‐4/C12SB‐MMT 5% respectively. Since PMBS‐4 and PMBS/C12SB‐MMT were examined in the absence of Li salt, the conductivity of samples was attributed to the motion of dipoles in chains of zwitterionic PMBS‐4. The increase in conductivity with increasing temperature was explained as a local structural relaxation and segmental motion of polymer. The values of σ, at 25 °C, for: PMBS‐4, PMBS‐4/C12SB‐MMT 1%, PMBS‐4/C12SB‐MMT 3% and PMBS‐4/C12SB‐MMT 5% were 6.2 × 10−6 S/cm, 1.2 × 10−6 S/cm, 1.7 × 10−6 S/cm and 9.1 × 10−6 S/cm respectively.

Quantum logic between remote quantum registers

We analyze two approaches to quantum state transfer in solid-state spin systems. First, we consider unpolarized spin-chains and extend previous analysis to various experimentally relevant imperfections, including quenched disorder, dynamical decoherence, and uncompensated long range coupling. In finite-length chains, the interplay between disorder-induced localization and decoherence yields a natural optimal channel fidelity, which we calculate. Long-range dipolar couplings induce a finite intrinsic lifetime for the mediating eigenmode; extensive numerical simulations of dipolar chains of lengths up to L=12 show remarkably high fidelity despite these decay processes. We further consider the extension of the protocol to bosonic systems of coupled oscillators. Second, we introduce a quantum mirror based architecture for universal quantum computing which exploits all of the spins in the system as potential qubits. While this dramatically increases the number of qubits available, the composite operations required to manipulate "dark" spin qubits significantly raise the error threshold for robust operation. Finally, as an example, we demonstrate that eigenmode-mediated state transfer can enable robust long-range logic between spatially separated Nitrogen-Vacancy registers in diamond; numerical simulations confirm that high fidelity gates are achievable even in the presence of moderate disorder.

Weak solutions to a nonlinear variational sine–Gordon equation

This paper considers a nonlinear variational sine–Gordon equation utt−c(u)[c(u)ux]x+λ22sin(2u)=0 which describes the motion of long waves on a neutral dipole chain in the continuum limit and a few other physical phenomena. We establish the global existence of dissipative weak solutions to its Cauchy problem for initial data in the space H1×L2 by using the Young measure theory in the setting of Lp spaces.

Increase in interparticle distance of colloidal dipolar chain in nematic liquid crystal by trapping it on splay-bend wall

We demonstrate an increase in the interparticle distance of a colloidal dipolar chain in a nematic liquid crystal (NLC). Applying an in-plane electric field perpendicular to the rubbing direction induces a splay-bend wall defect in the middle of the electrode gap, which traps a dipolar chain. Above the Freedericksz threshold electric field, the interparticle distance increases with increasing applied electric field, owing to the reorientation of the NLC molecules. The maximum increase is 32% of the particle diameter.

Novel complex phenomena in ferroelectric nanocomposites

A first-principles-based effective Hamiltonian is used to investigate finite-temperature properties of ferroelectric nanocomposites made of periodic arrays of ferroelectric nanowires embedded in a matrix formed by another ferroelectric material. Novel transitions and features related to flux-closure configurations are found. Examples include (i) a vortex core transition, that is characterized by the change of the vortex cores from being axisymmetric to exhibiting a ‘broken symmetry’; (ii) translational mode of the vortex cores; (iii) striking zigzag dipolar chains along the vortex core axis; and (iv) phase-locking of ferroelectric vortices accompanied by ferroelectric antivortices. These complex phenomena are all found to coexist with a spontaneous electrical polarization aligned along the normal of the plane containing the vortices.

Biological colloid engineering: Self-assembly of dipolar ferromagnetic chains in a functionalized biogenic ferrofluid

We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.

Modeling of the Voltage Waves in the LHC Main Dipole Circuits

When a fast power abort is triggered in the LHC main dipole chain, voltage transients are generated at the output of the power converter and across the energy-extraction switches. The voltage waves propagate through the chain of 154 superconducting dipoles and can have undesired effects leading to spurious triggering of the quench protection system and firing of the quench heaters. The phase velocity of the waves travelling along the chain changes due to the inhomogeneous AC behavior of the dipoles. Furthermore, complex phenomena of reflection and superposition are present in the circuit. For these reasons analytical calculations are not sufficient for properly analysing the circuit behavior after a fast power abort. The transients following the switch-off of the power converter and the opening of the switches are analysed by means of a complete electrical model, developed with the Cadence © suite (PSpice © based). The model comprises all the electrical components of the circuit, additional components simulating the dipole AC behavior, and the ground lines of the circuit including its parasitic capacitances. The simulation results are presented in order to illustrate the behavior of the circuit and to assess its performance under different operating conditions. The comparison between measurement data and simulations shows a very good agreement.

Impact of the Voltage Transients After a Fast Power Abort on the Quench Detection System in the LHC Main Dipole Chain

A Fast Power Abort in the LHC superconducting main dipole circuit consists in the switch-off of the power converter and the opening of the two energy-extraction switches. Each energy-extraction unit is composed of redundant electro-mechanical breakers, which are opened to force the current through an extraction resistor. When a switch is opened arcing occurs in the switch and a voltage of up to 1 kV builds up across the extraction resistor with a typical ramp rate of about 80 kV/s. The subsequent voltage transient propagates through the chain of 154 dipoles and superposes on the voltage waves caused by the switch-off of the power converter. The resulting effect caused intermittent triggering of the quench protection systems along with heater firings in the magnets when the transient occurred during a ramp of the current. A delay between power converter switch-off and opening of the energy-extraction switches was introduced to prevent this effect. Furthermore, the output filters of the power converters were modified in order to damp faster the voltage waves generated after the power-converter switch-off and to lower their amplitude. Finally, snubber capacitors were added in parallel to the extraction switches to help the commutation process by reducing the arcing effect and thus smoothing the voltage transient. A set of dedicated tests has been performed in order to understand the voltage transients and to assess the impact of the circuit modifications on the quench detection system. The results have been compared to the simulations of an electrical model of the LHC main dipole circuit developed with the Cadence suite (PSpice based).

Sedimentation equilibria of ferrofluids: II. Experimental osmotic equations of state of magnetite colloids

The first experimental osmotic equation of state is reported for well-defined magnetic colloids that interact via a dipolar hard-sphere potential. The osmotic pressures are determined from the sedimentation equilibrium concentration profiles in ultrathin capillaries using a low-velocity analytical centrifuge, which is the subject of the accompanying paper I. The pressures of the magnetic colloids, measured accurately to values as low as a few pascals, obey Van ’t Hoff’s law at low concentrations, whereas at increasing colloid densities non-ideality appears in the form of a negative second virial coefficient. This virial coefficient corresponds to a dipolar coupling constant that agrees with the coupling constant obtained via independent magnetization measurements. The coupling constant manifests an attractive potential of mean force that is significant but yet not quite strong enough to induce dipolar chain formation. Our results disprove van der Waals-like phase behavior of dipolar particles for reasons that are explained.

Long-Range Quantum Gates using Dipolar Crystals

We propose the use of dipolar spin chains to enable long-range quantum logic between distant qubits. In our approach, an effective interaction between remote qubits is achieved by adiabatically following the ground state of the dipolar chain across the paramagnet to crystal phase transition. We demonstrate that the proposed quantum gate is particularly robust against disorder and derive scaling relations, showing that high-fidelity qubit coupling is possible in the presence of realistic imperfections. Possible experimental implementations in systems ranging from ultracold Rydberg atoms to arrays of nitrogen vacancy defect centers in diamond are discussed.

Simulation for the Microstructure and Rheology in Bidisperse Magnetorheological Fluids

There are many ferromagnetic particles dispersed in carrier oil in magnetorheological fluids. Assuming Newtonian motion, the forces between particles of different radius, including magnetic interaction, viscous force and contact interaction, are obtained, and the corresponding model for motion of particles is proposed. Under an external magnetic field, the microstructures in bidisperse magnetorheological fluids are simulated, and the mechanical properties under both external magnetic field and macroscopic shear strain are investigated. The influence of attached particles on the side of dipolar chains is analyzed. It shows that particle size ratio in bidisperse suspensions can influence the performance of MR fluids.

Above-room-temperature ferroelectricity and antiferroelectricity in benzimidazoles

The imidazole unit is chemically stable and ubiquitous in biological systems; its proton donor and acceptor moieties easily bind molecules into a dipolar chain. Here we demonstrate that chains of these amphoteric molecules can often be bistable in electric polarity and electrically switchable, even in the crystalline state, through proton tautomerization. Polarization–electric field (P–E) hysteresis experiments reveal a high electric polarization ranging from 5 to 10 μC cm−2 at room temperature. Of these molecules, 2-methylbenzimidazole allows ferroelectric switching in two dimensions due to its pseudo-tetragonal crystal symmetry. The ferroelectricity is also thermally robust up to 400 K, as is that of 5,6-dichloro-2-methylbenzimidazole (up to ~373 K). In contrast, three other benzimidazoles exhibit double P–E hysteresis curves characteristic of antiferroelectricity. The diversity of imidazole substituents is likely to stimulate a systematic exploration of various structure–property relationships and domain engineering in the quest for lead- and rare-metal-free ferroelectric devices.

Shape-tuning the colloidal assemblies in nematic liquid crystals

Colloidal platelets are natural building blocks for the shape-controlled assembly of two-dimensional periodic lattices and can form versatile optical elements. Using three-dimensional (3D) numerical modelling, we demonstrate the self-assembly of triangular, square and pentagonal sub-micrometer sized platelets in a thin layer of nematic liquid crystal. Torques acting on individual platelets are calculated, showing that platelets with quadrupolar symmetry (squares, hexagons, etc) are, orientationally, more strongly bound than platelets with dipolar symmetry (triangles, pentagons) which is important for switching applications. Inter-platelet potentials are shown to depend in a complex way on the orientations of the platelets, exhibiting easy and hard reorientation axes and multiple minima. Linear chains of elastic dipoles form into two-dimensional periodic lattices via interesting rotational and translational shifts, to minimize the distortions in the surrounding nematic medium.

A qualitative confocal microscopy study on a range of colloidal processes by simulating microgravity conditions through slow rotations

We report qualitatively on the differences between colloidal systems left to evolve in the Earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsion above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsion, an unusual sequence of dilute-fluid–dilute-crystal–dense-fluid–dense-crystal phases was observed throughout the suspension under the effect of gravity. This was related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out of gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes.

Linear Viscoelastic and Uniaxial Extensional Rheology of Alkali Metal Neutralized Sulfonated Oligostyrene Ionomer Melts

The linear viscoelastic and nonlinear extensional behavior of melts of alkali metal salts of oligomeric sulfonated polystyrene (SPS) ionomers were characterized by dynamic shear and nonlinear, uniaxial extensional flow experiments. The oligomeric SPS had a weight-average molecular weight of 4000 g/mol, a polydispersity index of 1.06, and a degree of sulfonation of 6.5 mol %. The molecular weight was below the entanglement molecular weight of PS, so all rheological effects were due to association of the ionic dipoles and nanophase separation of the ionic species that provides a transient elastic network. The SPS salts exhibited linear viscoelastic properties similar to well-entangled polystyrene (PS) melts, with a distinct rubbery region that had a shear modulus comparable to that of high molecular weight PS. Time–temperature superposition failed as a consequence of overlapping relaxations for the terminal response of the chain and ion hopping of the ionic dipoles. Unlike entangled PS melts, the modulus of the ionomer increased with increasing extensional strain rate, and a maximum in the stress occurred at a relatively low Hencky strain that was nearly independent of strain rate. The maximum in the stress during stretching was attributed to a catastrophic failure of the physical ionic network. At sufficiently high stress, the chains can pull the ionic groups out of nanophase-separated ionic domains, which significantly disrupts the network microstructure.

Magnetic reversal of an artificial square ice: dipolar correlation and charge ordering

Magnetic reversal of an artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal axis is investigated via magnetic force microscopy of the remanent states that result. Sublattice independent reversal is observed via correlated incrementally pinned flip cascades along parallel dipolar chains, as evident from analysis of vertex populations and dipolar correlation functions. Weak dipolar interactions between adjacent chains favour antialignment and give rise to weak charge ordering of ‘monopole’ vertices during the reversal process.

Internal vibration energy in polyatomic molecules containing chains of identical biatomic dipoles

The quantum processes of excitation and vibrational energy transport that occur in polyatomic organic molecules under IR radiation are analyzed. The polyatomic organic molecules considered contain substructures with finite numbers of identical biatomic valence bonds, which play the role of antennas that trap and accumulate IR radiation. The result of this analysis can be used for determining the sequences of amino-acid residues in oligopeptides.