Combination Of Dipolar Interactions Research Articles

Effect of the surface anisotropy on the magnetic behavior of ultra-thin films single-domain on the spin reorientation transition regime by monte carlo simulation

In this work, Monte Carlo simulations allowed for studying the effect of the surface anisotropy on the Spin Reorientation Transition regime for single-domain ultra-thin films. The simulations included spin moments (1), exchange constant (10 meV), magnetocrystalline anisotropy (0.5 meV), and dipolar magnetic interaction (0.05 meV). We evaluated the surface anisotropy constant for K S = 0.5, 1, and 2 meV and thicknesses ranging from 3 to 11 cells. We determined the magnetothermal and hysteresis loop in- and out-plane at different angles to the plane. Analysis of Variance allows for modeling the coercivity as a function of the thickness and the applied field direction (in- and out-plane). Under these simulation conditions, the Spin Reorientation Transitions appear only at a thickness of 7 cells with K S =1 meV. The main contribution to magnetization rises out-plane at low thicknesses and in-plane at high values. However, the dominant magnetization contribution is in-plane for the thickness of 7 cells and low surface anisotropy. The magnetization is mainly oriented, out-plane for the high surface anisotropy case. However, hysteresis loops were observed independent of the applied magnetic field direction and thickness. Analysis of Variance results suggests that the thickness and the applied magnetic field direction allowed for tunning the coercivity (hard or soft magnetic materials). Sample simulated ignoring the magnetocrystalline and the surface anisotropies produce magnetic components in- and out-plane with slight differences as angle function. The combination of dipolar interactions and magnetocrystalline anisotropy showed two magnetic behaviors, a hard magnetic phase at low angles and a soft one at high angles in-plane direction. The inverse behavior results in the out-plane component. We observed the same behavior when surface anisotropy is considered. The differences are the transition angle of 50° in the first case and 30° in the second.

Self‐Healable Fluorinated Copolymers Governed by Dipolar Interactions

Although dipolar forces between copolymer chains are relatively weak, they result in ubiquitous inter‐ and/or intramolecular interactions which are particularly critical in achieving the mechanical integrity of polymeric materials. In this study, a route is developed to obtain self‐healable properties in thermoplastic copolymers that rely on noncovalent dipolar interactions present in essentially all macromolecules and particularly fluorine‐containing copolymers. The combination of dipolar interactions between C─F and C═O bonds as well as CH2/CH3 entities facilitates self‐healing without external intervention. The presence of dipole‐dipole, dipole‐induced dipole, and induced‐dipole induced dipole interactions leads to a viscoelastic response that controls macroscopic autonomous multicycle self‐healing of fluorinated copolymers under ambient conditions. Energetically favorable dipolar forces attributed to monomer sequence and monomer molar ratios induces desirable copolymer tacticities, enabling entropic energy recovery stored during mechanical damage. The use of dipolar forces instead of chemical or physical modifications not only eliminates additional alternations enabling multiple damage‐repair cycles but also provides further opportunity for designing self‐healable commodity thermoplastics. These materials may offer numerous applications, ranging from the use in electronics, ion batteries, H2 fuel dispense hoses to self‐healable pet toys, packaging, paints and coatings, and many others.

Self-assembly of taper-shaped monoesters of oligo(ethylene oxide) with 3,4,5-tris(n-dodecan-1-yloxy)benzoic acid and of their polymethacrylates into tubular supramolecular architectures displaying a columnar hexagonal mesophase

The synthesis of the monoesters of oligo(ethylene oxide) and octane-1,8-diol with 3,4,5-tris(n-alkan-1-yloxy)benzoic acids and of their corresponding polymethacrylates is described. The LiCF3SO3 complexes of the monoesters of triethylene glycol with 3,4,5-tris(n-dodecan-1-yloxy)-benzoic acid (3-12-3), and with 3,4,5-tris(n-octadecan-1-yloxy)benzoic acid (3-18-3), as well as the polymethacrylates of the monoesters of mono-(5-12-1),di-(5-12-2), tri-(5-12-3) and tetra-(5-12-4) ethylene glycol with 3,4,5-tris(n-dodecan-1-yloxy)benzoic acid self-assemble into a cylindrical supramolecular architecture which displays a columnar hexagonal (Φh) mesophase. This cylindrical supramolecular architecture was characterized by a combination of techniques including differential scanning calorimetry, wide- and small-angle X-ray scattering, thermal optical polarized microscopy, and molecular modelling. The characterization results suggest a model that resembles the cylindrical architecture that forms by the self-assembly of low molar mass and polymerized inverse micelles. A cross-section of the cylindrical assembly is constituted of about five molecules of 3-12-3 in its LiCF3SO3 complex or about four to five repeats units of 5-12-n with their oligooxyethylenic segments melted and segregated in the inner core of the cylinder and their melted alkyl tails radiating towards the periphery of the cylinder. The driving force for the cylindrical self-assembly is provided by a fine balance of exo- and endo-recognition processes. Exo-recognition is the result of the tapered shape and hydrophobic character of the 3,4,5-tris(n-dodecan-1-yloxy)benzoate group. Endo-recognition is generated by either the combination of dipolar and ionic interactions of the oligo(ethylene oxide) receptor (LiCF3SO3 complex of 3-12-3) or the combination of dipolar interactions and covalent bonding (5-12-n). The necessity of the presence of endo-recognition for the self-assembly of the cylindrical supramolecular architecture is demonstrated by the replacement of the oligo(ethylene oxide) receptor by a non-polar aliphatic spacer. Comparison between the ‘molecular’ polymethacrylate backbone (in 5-12-3) and the ‘supramolecular polymer backbone’(formed via ionic interactions in the complex of 3-12-3) indicates that in this particular example, the ionic interactions generated by the dissolved ion-pairs stabilize the supramolecular assembly to a greater extent than does the covalent bonding.