Weak Interchain Interactions Research Articles

Dependence of Polymer Thin Film Adhesion Energy on Cohesive Interactions between Chains

Substrate–film interfacial properties play a fundamental role in the adhesion of glassy polymer thin films onto supporting substrates. Utilizing steered molecular dynamics (SMD) simulations, here we uncover that the cohesive noncovalent forces between polymer chains also have a significant effect on the adhesive properties of polymer films in contact with flat substrates. We demonstrate that weaker interchain interactions, all else being the same, can induce higher adhesion energy within the interface. Three different regimes in the adhesion energy profile can be characterized by a nonlinear scaling relationship. In the weak substrate–film interaction regime, the adhesion energy of the film exhibits near independence of cohesive force variations, and the entropic contributions to the surface free energy are consequential. In the intermediate regime, films with weaker cohesive forces exhibit higher adhesion energy due to the ability of polymer chains to pack more effectively in the interfacial region, thereby increasing the adhesive interaction density. In the strong interaction regime, the adhesion energy increases linearly with the adhesive interaction strength because of saturation of local packing in the interfacial region. These findings corroborate recent polymer dewetting observations that have hinted on the importance of local relaxation and packing effects on interfacial properties.

Coupled Effects of Substrate Adhesion and Intermolecular Forces on Polymer Thin Film Glass-Transition Behavior

Intermolecular noncovalent forces between polymer chains influence the mobility and glass-transition temperature (Tg), where weaker interchain interactions, all else being the same, typically results in lower bulk polymer Tg. Using molecular dynamics simulations, here we show that this relation can become invalid for supported ultrathin films when the substrate-polymer interaction is extremely strong and the polymer-polymer interactions are much weaker. This contrasting trend is found to be due to a more pronounced substrate-induced appreciation of the film Tg for polymers with weaker intermolecular interactions and low bulk Tg. We show that optimizing this coupling between substrate adhesion and bulk Tg maximizes thin film Tg, paving the way for tuning film properties through interface nanoengineering.

μSR study of magnetic order in the organic quasi-one-dimensional ferromagnet F4BImNN

The stable organic radical 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) forms hydrogen-bonded chains in the solid state and exhibits one-dimensional ferromagnetic exchange with $J/{k}_{\mathrm{B}}=22$ K. We use muon-spin rotation to demonstrate that weak interchain interactions drive the system to long-range magnetic order below ${T}_{\mathrm{c}}=0.72$ K. We use density-functional calculations of the muon site and compare our results to those obtained on the nonfluorinated analog compound. Our results show that F4BImNN is the best realization of a one-dimensional Heisenberg ferromagnet among purely organic compounds yet discovered.

Electron-Deficient Poly(p-phenylene vinylene) Provides Electron Mobility over 1 cm2 V–1 s–1 under Ambient Conditions

Poly(p-phenylene vinylene) derivatives (PPVs) are one of the most widely investigated p-type polymers in organic electronics. PPVs generally exhibit electron mobilities lower than 10(-4) cm(2) V(-1) s(-1), thus hindering their applications in high-performance polymer field-effect transistors and organic photovoltaics. Herein, we design and synthesize a novel electron-deficient PPV derivative, benzodifurandione-based PPV (BDPPV). This new PPV derivative displays high electron mobilities up to 1.1 cm(2) V(-1) s(-1) under ambient conditions (4 orders of magnitude higher than those of other PPVs), because it overcomes common defects in PPVs, such as conformational disorder, weak interchain interaction, and a high LUMO level. BDPPV represents the first polymer that can transport electrons over 1 cm(2) V(-1) s(-1) under ambient conditions.

Uranyl–copper(ii) heterometallic oxalate complexes: coordination polymers and frameworks

Five oxalate complexes containing both uranyl and copper(II) ions and 2,2′-bipyridine (bipy), 2,2′-bipyrimidine (bipym) or 1,10-phenanthroline (phen) as co-ligands have been synthesized under hydrothermal conditions and their crystal structures were determined. [UO2Cu(C2O4)(NO3)2(bipy)(H2O)] (1) is a molecular complex in which the two cations are connected by the bis-chelating oxalate. A one-dimensional uranyl oxalate ribbon is formed in [UO2Cu(C2O4)2(bipym)(H2O)] (2), with uranyl ions bound to two chelating anions and to a third, monodentate oxalate which holds the decorating [Cu(bipym)(H2O)]2+ groups. Complex [(UO2)2Cu2(C2O4)2(bipym)3(OH)2]·2NO3 (3) is a two-dimensional assembly in which uranyl oxalate chains are linked to one another by [Cu2(bipym)3]4+ dinuclear units through bridging hydroxide ions. Finally, [UO2Cu(C2O4)2(bipy)] (4) and [UO2Cu(C2O4)2(phen)] (5) display identical three-dimensional arrangements containing uranyl oxalate sheets connected to one another by copper oxalate dinuclear units. The magnetic properties of compounds 2 and 4 have been investigated. Weak inter-chain antiferromagnetic interactions between copper(II) atoms are present in 2, while 4 displays strong oxalate-mediated antiferromagnetic exchange (J = -335 cm(-1)). These complexes are the first uranyl-d block metal oxalate complexes to be reported.

Synthesis, structure, and magnetic properties of a cyanidebridged Fe(III)-Cu(II) bimetallic double-zigzag chain with slow relaxation of the magnetization

Using Bu4N[Fe(Tp*)(CN)3]− (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) as the building block to react with CuII and N-methylimidazole, we obtained a one-dimensional (1D) heterobimetallic cyano-bridged chain, [Fe(Tp*)(CN)3]2Cu(N-methylimidazole)2·2H2O (1). The crystal structures and magnetic studies demonstrate that complex 1 exhibits slow relaxation of the magnetization due to strong intrachain ferromagnetic coupling and weak interchain interactions.

A Ferromagnetic Methoxido-Bridged Mn(III) Dimer and a Spin-Canted Metamagnetic μ1,3-Azido-Bridged Chain

Two new Mn(III) complexes of formulas [MnL(1)(N(3))(OMe)](2) (1) and [MnL(2)(N(3))(2)](n) (2) have been synthesized by using two tridentate NNO-donor Schiff base ligands HL(1){(2-[(3-methylaminoethylimino)-methyl]-phenol)} and HL(2) {(2-[1-(2-dimethylaminoethylimino)methyl]phenol)}, respectively. Substitution of the H atom on the secondary amine group of the N-methyldiamine fragment of the Schiff base by a methyl group leads to a drastic structural change from a methoxido-bridged dimer (1) to a single μ(1,3)-azido-bridged 1D helical polymer (2). Both complexes were characterized by single-crystal X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The magnetic properties of compound 1 show the presence of weak ferromagnetic exchange interactions mediated by double methoxido bridges (J = 0.95 cm(-1)). Compound 2 shows the existence of a weak antiferromangetic coupling along the chain (J = -8.5 cm(-1)) through the single μ(1,3)-N(3) bridge with a spin canting that leads to a long-range antiferromagnetic order at T(c) ≈ 9.3 K and a canting leading to a weak ferromagnetic long-range order at T(c) ≈ 8.5 K. It also exibits metamagnetic behavior at low temperatures with a critical field of ca.1.2 T due to the weak antiferromagnetic interchain interactions that appear in the canted ordered phase.

Study of Low Temperature Magnetic Properties of a Single Chain Magnet with Alternate Isotropic and Non-collinear Anisotropic Units

Here we study thermodynamic properties of an important class of single-chain magnets (SCMs), where alternate units are isotropic and anisotropic with anisotropy axes being non-collinear. This class of SCMs shows slow relaxation at low temperatures which results from the interplay of two different relaxation mechanisms, namely dynamical and thermal. Here anisotropy is assumed to be large and negative, as a result, anisotropic units behave like canted spins at low temperatures; but even then simple Ising-type model does not capture the essential physics of the system due to quantum mechanical nature of the isotropic units. We here show how statistical behavior of this class of SCMs can be studied using a transfer matrix (TM) method. We also, for the first time, discuss in detail how weak inter-chain interactions can be treated by a TM method. The finite size effect is also discussed which becomes important for low temperature dynamics. At the end of this paper, we apply this technique to study a real helical chain magnet.

First-principles study of magnetic interactions in cupric oxide

Cupric oxide (CuO) has been described as belonging to the quasi-one-dimensional antiferromagnetic compounds. It has also been suggested that cupric oxide possesses strong magnetic anisotropy, which is possibly related to the observed ferroelectricity in this material. In this paper, the magnetic interactions of CuO are investigated using the embedded cluster approach. Accurate wave-function-based methods have been employed to describe the interactions along all copper-oxygen chain directions. Both two-center and three-center clusters are considered in our calculations. The antisymmetric anisotropic interaction parameters are also calculated for the two-center clusters by applying an effective Hamiltonian theory. Our results show that the magnetic interactions are dominated by the antiferromagnetic coupling between copper ions along the chain of largest Cu-O-Cu angles in agreement with experiment. The results for the interplane magnetic interactions reveal competition between nearest-neighbor ferromagnetic coupling and second-nearest-neighbor antiferromagnetic interaction along the direction where two copper ions are connected via doubly bridged oxygen ligands. We also find nonnegligible Dzyaloshinskii-Moriya interactions with magnitude comparable to the weak isotropic interchain interactions.

Neutron scattering andμSR investigations of quasi-one-dimensional magnetism in the spin=3/2compound Li3RuO4

The $S$ = 3/2, quasi-one-dimensional (1D) zig-zag chain Heisenberg antiferromagnet Li${}_{3}$RuO${}_{4}$ has been investigated using heat capacity, inelastic neutron scattering, neutron diffraction, and \ensuremath{\mu}SR measurements on a powder sample. Our neutron diffraction and \ensuremath{\mu}SR studies confirm a long-range ordering of the magnetic moments on the Ru${}^{5+}$ cations below 40 K. The magnetic excitations were measured at various temperatures above and below the three-dimensional (3D) ordering temperature in order to understand the broad peak observed in the temperature dependence of the magnetic susceptibility. At 5 K we have observed two well-defined magnetic excitations at 5.5 meV and 8.5 meV and a weak low-energy peak near \ensuremath{\sim}2 meV. We interpret the 5.5 meV energy peak as a 1D zone-boundary mode and that at 8.5 meV as arising from a maximum away from the zone boundary in the dispersion curve for spin-wave modes along the chain of Ru${}^{5+}$ ions. The weaker peak near 2 meV is thought to arise from a weak interchain coupling. Our data are best reproduced using a model with three intrachain interactions and one weak interchain interaction. The experimental spin-exchange interactions are in good agreement with those calculated for a 1D model by density functional theory (DFT) methods. Furthermore, above ${T}_{N}$ we observe strong diffuse scattering at the same $Q$-position as the 5.5 meV mode, which suggests the presence of short-range magnetic correlations above ${T}_{N}$. We have estimated the correlation length \ensuremath{\xi} \ensuremath{\sim} 2.9 \AA{} at 50 K, which is close to 2.99 \AA{}, the shortest distance between the Ru${}^{5+}$ cations along the zig-zag chain.

Suppression of magnetic ordering in quasi-one-dimensional FexCo1−xNb2O6compounds

We present a systematic investigation of the series of compounds Fe${}_{x}$Co${}_{1\ensuremath{-}x}$Nb${}_{2}$O${}_{6}$ by means of x-ray and neutron powder diffraction combined with magnetic measurements, carried out in the paramagnetic as well as in the ordered state, to probe the stability of the magnetic ordering against the composition changes in this model Ising system. Fe for Co substitution induces a continuous lattice volume increase, preserving the orthorhombic crystal structure. The unit-cell expansion is anisotropic and occurs mainly in the $\mathit{ab}$ plane. The observed magnetic structures for $x=0,0.8$, and 1 are described by the propagation vectors $(0,1/2,0)$ and $(1/2,1/2,0)$, and are consistent with the picture of ferromagnetic Ising-type chains of Fe/Co spins antiferromagnetically coupled by weak interchain interactions. We find out that for $0<x<0.8$, substitution tends to suppress magnetic order, with the studied compounds remaining disordered down to 1.7 K. Our estimate of the exchange integrals for the ordered compound at $x=0.8$ indicates that the Fe/Co cation disorder induces a substantial drop of the average exchange strength both within and between the Ising chains, reflecting the tendency to suppression of long-range magnetic order.

Theoretical study of intra- and inter-chain magnetic interactions in [Ni(chxn) 2Br]Br 2

The intra- and the inter-chain magnetic interactions in [Ni(chxn) 2Br]Br 2, which is one of the typical one-dimensional (1-D) MX complexes are examined by using an unrestricted hybrid DFT (UB3LYP) method. Calculated effective exchange integral ( J) value along the 1-D chain is 2 J Intra = −4016 K and is close to an experimental result (−3600 K). On the other hand, a very weak anti-ferromagnetic inter-chain interaction through Br − ions is observed. The value is estimated to be 2 J Inter = −2 to −6 K. In addition to the J values, transfer integral ( t), on-site Coulomb repulsion ( U) and charge transfer energy ( E CT) values along the 1-D chain are also estimated to be 0.46, 2.46 and 0.6 eV, respectively.

Structural diversity and magnetic properties in 1D and 2D azido-bridged cobalt(ii) complexes with 1,2-bis(2-pyridyl)ethylene

By utilizing a flexible co-ligand 1,2-bis(2-pyridyl)ethylene (2,2'-bpe), two new azido-bridged cobalt(II) complexes with the formulae [Co₃(N₃)₆(OH₂)₂(2,2'-bpe)₂](n)(2,2'-bpe)(n) (1) and [Co(N₃)₂(2,2'-bpe)₂](n) (2) have been synthesized and structurally characterized. Compound 1 shows an uncommon 1D chain comprised of double EO azido bridged five- and six-coordinated Co(II) geometries in a unique (-5-5-6-)(n) sequence of the coordination number. The 2,2'-bpe acts as a terminal co-ligand and an uncoordinated molecule in the crystal lattice. Moreover the adjacent 1D chain is assembled by C-Hπ interactions and the intermolecular hydrogen bonding between uncoordinated 2,2'-bpe and coordinated water molecules building a 2D layer. Whereas, compound 2 is a 2D coordination network containing the alternating double EO and double EE bridging modes of azides and ditopic 2,2'-bpe bridges. The magnetic investigation of 1 reveals dominant intra-chain ferromagnetic interactions, with the double EO azide-bridge and weak inter-chain antiferromagnetic interactions, with overall metamagnetic behaviour, having magnetic ordering at 6 K. The magnetic behaviour of 2 shows spin-canted antiferromagnetism below a T(N) of 12 K.

Diverse Structures and Magnetism of Cobalt(II) and Manganese(II) Compounds with Mixed Azido and Carboxylato Bridges Induced by Methylpyridinium Carboxylates

Herein we present a systematic study of the structures and magnetic properties of six coordination compounds with mixed azide and zwitterionic carboxylate ligands, [M(N(3) )(2) (2-mpc)] (2-mpc=N-methylpyridinium-2-carboxylate; M=Co for 1 and Mn for 2), [M(N(3) )(2) (4-mpc)] (4-mpc=N-methylpyridinium-4-carboxylate; M=Co for 3 and Mn for 4), [Co(3) (N(3) )(6) (3-mpc)(2) (CH(3) OH)(2) ] (5), and [Mn(3) (N(3) )(6) (3-mpc)(2) ] (6; 3-mpc=N-methylpyridinium-3-carboxylate). Compounds 1-3 consist of one-dimensional uniform chains with (μ-EO-N(3) )(2) (μ-COO) triple bridges (EO=end-on); 5 is also a chain compound but with alternating [(μ-EO-N(3) )(2) (μ-COO)] triple and [(EO-N(3) )(2) ] double bridges; Compound 4 contains two-dimensional layers with alternating [(μ-EO-N(3) )(2) (μ-COO)] triple, [(μ-EO-N(3) )(μ-COO)] double, and (EE-N(3) ) single bridges (EE=end-to-end); 6 is a layer compound in which chains similar to those in 5 are cross-linked by a μ(3) -1,1,3-N(3) azido group. Magnetically, the three Co(II) compounds (1, 3, and 5) all exhibit intrachain ferromagnetic interactions but show distinct bulk properties: 1 displays relaxation dynamics at very low temperature, 3 is an antiferromagnet with field-induced metamagnetism due to weak antiferromagnetic interchain interactions, and 5 behaves as a noninnocent single-chain magnet influenced by weak antiferromagnetic interchain interactions. The magnetic differences can be related to the interchain interactions through π-π stacking influenced by different substitution positions in the ligands and/or different magnitudes of intrachain coupling. All of the Mn(II) compounds show overall intrachain/intralayer antiferromagnetic interactions. Compound 2 shows the usual one-dimensional antiferromagnetism, whereas 4 and 6 exhibit different weak ferromagnetism due to spin canting below 13.8 and 4.6 K, respectively.

Ising Chains Antiferromagnetically Coupled on a Triangular Lattice

We have investigated models composed of infinitely many Ising magnetic chains creating a triangular or hexagonal lattice. These models with nearest-neighbor antiferromagnetic interactions are frustrated and it is known that the first one is disordered at all finite temperatures, whereas the second one undergoes a finite temperature continuous phase transition to a phase with a three-sublattice structure. The Linear Perturbation Renormalization Group is used to predict the critical temperature for the Ising chains with ferro- or antiferromagnetic intrachain interaction ( k = J / k B T ) coupled by weaker interchain interactions ( k 1 = J '/ k B T ). The inverse critical temperature k c as function of k 1 / k is found for the systems in two and three dimensions for both ferro- and antiferromgnetic interactions. For the standard ferromagnetic Ising model ( k 1 = k ) on the triangular lattice we have found k c = 0.268 which should be compared with the exact value k c = 0.274. We have also calculated the speci...

Analysis on the exchange interactions in three metal-organic coordination network systems possessing one-dimensional magnetism

The nature of the exchange interactions in three metal-organic coordination networks families is examined. These families have a general form ML2(bpy). Since (bpy) molecules are very long, our networks are reduced to effectively one-dimensional chain systems with very weak interchain interaction. The Bonner–Fisher and Fisher classical spin models are applied to fit the magnetic susceptibility data, and results of the fits are discussed. Metal ions inside MCl2(bpy) and M(N3)2(bpy) interact with ferromagnetic interactions and can be described with Fisher classical spin model, while metal ions in M(ox)(bpy) interact with antiferromagnetic interaction and it can be described with the Bonner–Fisher model. Fitting parameter J produced from our models has higher value in M(N3)2(bpy) than in MCl2(bpy) for the same M. It was found that the total spin value is dominant factor to the strength of the magnetic interaction.

Low Cost, Environmentally Friendly, In Situ Prepared Quasi-Solid-State AlI[sub 3] Electrolyte for Dye-Sensitized Solar Cells

The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magnetosomes, which are arranged in the form of linear fragmental chain. The distinct differences of magnetic properties between these two samples can be faithfully interpreted in terms of spatial arrangement of magnetosomes and magnetostatic interaction. For the whole cells, the strong intra-chain interactions and weak inter-chain interactions generate behaviors of non-interacting uniaxial single-domain particles. Its delta-ratio is 3.0 and passes the Moskowitz test. In contrast, the isolated magnetosome sample has reduced values of coercivity and delta-ratio (1.5), due to increasing three-dimensional magnetostatic interactions and collapse of magnetosome chains. These observations provide useful insights into applications of the biogenic magnetite (magnetosomes) in magnetic nano-materials and magnetofossils in the paleomagnetic and environmental magnetism.

A comparative study of magnetic properties between whole cells and isolated magnetosomes of Magnetospirillum magneticum AMB-1

The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magnetosomes, which are arranged in the form of linear fragmental chain. The distinct differences of magnetic properties between these two samples can be faithfully interpreted in terms of spatial arrangement of magnetosomes and magnetostatic interaction. For the whole cells, the strong intra-chain interactions and weak inter-chain interactions generate behaviors of non-interacting uniaxial single-domain particles. Its δ-ratio is 3.0 and passes the Moskowitz test. In contrast, the isolated magnetosome sample has reduced values of coercivity and δ-ratio (1.5), due to increasing three-dimensional magnetostatic interactions and collapse of magnetosome chains. These observations provide useful insights into applications of the biogenic magnetite (magnetosomes) in magnetic nano-materials and magnetofossils in the paleomagnetic and environmental magnetism.

Polymer Solar Cells Based on Alternating and Statistical 4,7-Bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole Copolymers

A series of copolymers based on variable contents of 4,7-bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole (1) and dioctylfluorene were synthesized by Suzuki, Yamamoto and oxidative coupling methods. The octylphenyl substituent introduced on 1 confers high solubility and enables high-molecular-weight polymers to be synthesized. Using the different methods of polymerization, the content of 1 may be tuned to cover the range of absorption profiles over the visible spectrum, and the sequence distribution can be varied from alternating to statistical. Suzuki coupling provided copolymers in which 1 is flanked by dioctylfluorene units and that exhibited a high quantum yield of photoluminescence. A corresponding alternating polymer, poly[dioctylfluorene-alt-4,7-bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole], prepared by Suzuki coupling, exhibits a higher photoluminescent quantum efficiency of 0.54 in the solid state and small red-shifts of its absorption and emission spectra from solution to solid, indicating weaker interchain interactions. Polymer-fullerene bulk heterojunction devices based on alternating copolymers provided an open circuit voltage of 1.15 V and a power conversion efficiency of 0.92%, much higher than statistical copolymer and homopolymer of 1.

Magnetic Frustration and Spin Disorder in Isostructural M(μ-OH2)2[Au(CN)2]2 (M = Mn, Fe, Co) Coordination Polymers Containing Double Aqua-Bridged Chains: SQUID and μSR Studies

A series of isostructural M(mu-OH(2))(2)[Au(CN)(2)](2) (M = Co, Fe, and Mn) coordination polymers was synthesized from the reaction of M(II) with [(n)Bu(4)N][Au(CN)(2)]. The basic structural motif for these polymers is analogous to that of previously reported Cu(II)- and Ni(II)-containing polymers and contains repeating double aqua bridges between metal centers that yield a chain structure with pendant [Au(CN)(2)](-) units. The aqueous reaction with Fe(III) yields Fe(mu-OH(2))(mu-OH)[Au(CN)(2)](2), which has a similar structure. The magnetic properties of these polymers were investigated by a combination of SQUID magnetometry and zero-field muon spin relaxation. The double aqua bridges were found to mediate ferromagnetic interactions along the chains in the Co(II)-containing polymer, whereas intrachain antiferromagnetic interactions are present in the Fe(II)-, Fe(III)-, and Mn(II)-containing polymers. Weak magnetic interchain interactions mediated through hydrogen bonds, involving the bridging water molecules and the pendant cyanide groups, are also present. In zero field, the interchain interactions yield a phase transition to a disordered spin-frozen magnetic state below 2-5 K for every polymer. However, the degree of spin disorder varies considerably, depending on the metal center.