Role Of Attractive Interactions Research Articles

Finite-size scaling and thermodynamics of model supercooled liquids: long-range concentration fluctuations and the role of attractive interactions.

We compute partial structure factors, Kirkwood-Buff integrals (KBIs) and chemical potentials of model supercooled liquids with and without attractive interactions. We aim at investigating whether relatively small differences in the tail of the radial distribution functions result in contrasting thermodynamic properties. Our results suggest that the attractive potential favours the nucleation of long-range structures. Indeed, upon decreasing temperature, Bathia-Thornton structure factors display anomalous behaviour in the k→0 limit. KBIs extrapolated to the thermodynamic limit confirm this picture, and excess coordination numbers identify the anomaly with long-range concentration fluctuations. By contrast, the purely repulsive system remains perfectly miscible for the same temperature interval and only reveals qualitatively similar concentration fluctuations in the crystalline state. Furthermore, differences in both isothermal compressibilities and chemical potentials show that thermodynamics is not entirely governed by the short-range repulsive part of the interaction potential, emphasising the nonperturbative role of attractive interactions. Finally, at higher density, where both systems display nearly identical dynamical properties and repulsive interactions become dominant, the anomaly disappears, and both systems also exhibit similar thermodynamic properties.

Role of Attractive Interactions in Structure Ordering and Dynamics of Glass-Forming Liquids

A key question in glass physics is what the origin of slow glassy dynamics is. The liquid structure is a natural candidate; however, an apparently severe counterexample has been known. Two model glass-forming liquids, with the standard Lennard-Jones interaction potential and its Weeks-Chandler-Andersen variation without the attractive tail, exhibit very similar structures at the two-body level but drastically different dynamical behaviors in the supercooled states. Here we look at the liquid structure through a (many-body) structural order parameter Θ characterizing the packing capability of local particle arrangements. We show that the structures of these two systems seen by Θ are actually very different at a many-body level, but, quite surprisingly, the macroscopic structure (Θ)-dynamics (τ_{α}) relationships commonly follow a Vogel-Fulcher-Tammann-like function. Furthermore, the mutual information analysis reveals strong local structure-dynamics correlations. Therefore, we conclude that attractive interactions affect the liquid structure in a nonperturbative manner, but a general structural origin of slow dynamics holds for these systems.

Communication: Polymer entanglement dynamics: Role of attractive interactions.

The coupled dynamics of entangled polymers, which span broad time and length scales, govern their unique viscoelastic properties. To follow chain mobility by numerical simulations from the intermediate Rouse and reptation regimes to the late time diffusive regime, highly coarse grained models with purely repulsive interactions between monomers are widely used since they are computationally the most efficient. Here using large scale molecular dynamics simulations, the effect of including the attractive interaction between monomers on the dynamics of entangled polymer melts is explored for the first time over a wide temperature range. Attractive interactions have little effect on the local packing for all temperatures T and on the chain mobility for T higher than about twice the glass transition Tg. These results, across a broad range of molecular weight, show that to study the dynamics of entangled polymer melts, the interactions can be treated as pure repulsive, confirming a posteriori the validity of previous studies and opening the way to new large scale numerical simulations.

Phase separation of a Lennard-Jones fluid interacting with a long, condensed polymer chain: implications for the nuclear body formation near chromosomes.

Phase separation in a biological cell nucleus occurs in a heterogeneous environment filled with a high density of chromatins and thus it is inevitably influenced by interactions with chromatins. As a model system of nuclear body formation in a cell nucleus filled with chromatins, we simulate the phase separation of a low-density Lennard-Jones (LJ) fluid interacting with a long, condensed polymer chain. The influence of the density variation of LJ particles above and below the phase boundary and the role of attractive interactions between LJ particles and polymer segments are investigated at a fixed value of strong self-interaction between LJ particles. For a density of LJ particles above the phase boundary, phase separation occurs and a dense domain of LJ particles forms irrespective of interactions with the condensed polymer chain whereas its localization relative to the polymer chain is determined by the LJ-polymer attraction strength. Especially, in the case of moderately weak attractions, the domain forms separately from the polymer chain and subsequently associates with the polymer chain. When the density is below the phase boundary, however, the formation of a dense domain is possible only when the LJ-polymer attraction is strong enough, for which the domain grows in direct contact with the interacting polymer chain. In this work, different growth behaviors of LJ particles result from the differences in the density of LJ particles and in the LJ-polymer interaction, and this work suggests that the distinct formation of activity-dependent and activity-independent nuclear bodies (NBs) in a cell nucleus may originate from the differences in the concentrations of body-specific NB components and in their interaction with chromatins.

Interactions between Dyes and Cetyl-trimethyl Ammonium Bromide

Abstract Surfactants have been widely used as auxiliaries in many areas of textile finishing. The nature of the interactions between dyes and surfactants is one of the basic piece of information for understanding the process of dyeing and finishing of textile material. The role of attractive interactions between the hydrocarbon tails and repulsive interactions between the surfactant head groups on the micellar association process have been studied. The presented work is oriented on the determination of the critical micelle concentration and molar conductance, in aqueous solution of cationic surfactant cetyltrimethyl ammonium bromide by using the electric conductivity method. From conductivity data parameters for dyes – surfactant interaction such as micellar ionization degree α, counter ion binding and free energy of micellization have been calculated. On the basis of results it is clear that critical micelle concentration depends on the nature of ionic group and concentration of counter ion in solution.

Ions in water: Role of attractive interactions in size dependent diffusivity maximum

A molecular dynamics study of model ions in water is reported. The van der Waals diameter of both the cations and anions is varied. We have carried out two sets of simulations--with and without dispersion interaction--between the ion and water. Self-diffusivity of the ions exhibits an anomalous maximum as a function of the van der Waals diameter for both these sets. This existence of a maximum in self-diffusivity when there is no dispersion interaction between the ion and the water is attributed to the attractive term from electrostatic interactions. Detailed analysis of this effect shows that the solvent shell is more strongly defined in the presence of dispersion interactions. A smaller ion exhibits biexponential decay while a single exponential decay is seen for the ion with maximum diffusivity in the self-part of the intermediate scattering function. The solvent structure around the ion appears to determine much of the dynamics of the ion. Interesting trends are seen in the activation energies and these can be understood in terms of the levitation effect.

Field-induced layering of confined ferromagnetic nanoparticles: the role of attractive interactions

We present Molecular Dynamics simulation results for confined ferromagnetic nanoparticles (film geometry) under the influence of strong, homogeneous magnetic fields. We focus on the role of short-ranged attractive interactions between the particles for the structure formation in thin films consisting of four to five monolayers. To this end we compare simulation results for Stockmayer particles (Lennard-Jones plus dipolar interactions) with corresponding results for dipolar soft spheres, where the short-ranged potential is purely repulsive. At moderate and large average densities, both systems exhibit pronounced layering. Based on the corresponding normal pressure oscillations we show that the field-induced effects on the layer formation in this density range are essentially independent of the short-range interactions. The dipolar soft sphere system merely has a stronger tendency to form a crystal-like lateral structure upon application of a parallel field. More pronounced differences occur at lower densities and not too high dipolar coupling strengths within the vapour–liquid region of the confined, zero-field Stockmayer system. Applying a perpendicular field, the Stockmayer system develops a blob structure absent in the corresponding repulsive system. Finally, for very large values of both, dipolar coupling parameter and field strength of a perpendicular field, we find evidence for a field-induced in-plane crystallisation of the layered systems.

Spin-density-functional theory for imbalanced interacting Fermi gases in highly elongated harmonic traps

We numerically study imbalanced two component Fermi gases with attractive interactions in highly elongated harmonic traps. An accurate parametrization formula for the ground state energy is presented for a spin-polarized attractive Gaudin-Yang model. Our studies are based on an accurate microscopic spin-density-functional theory through the Kohn-Sham scheme which employs the one-dimensional homogeneous Gaudin-Yang model with a Luther-Emery-liquid ground-state correlation as a reference system. A Thomas-Fermi approximation is examined incorporating the exchange-correlation interaction. By studying the charge and spin density profiles of the system based on these methods, we gain a quantitative understanding of the role of attractive interactions and polarization on the formation of the two-shell structure, with the coexisted Fulde-Ferrell-Larkin-Ovchinnikov-type phase in the center of the trap and either the BCS superfluid phase or the normal phase at the edges of the trap. Our results are in good agreement with the recent theoretical consequences.

The role of interfacial interactions in the dynamic mechanical response of functionalized SWNT–PS nanocomposites

The dynamic mechanical properties of nanocomposites of functionalized single-walled carbon nanotubes dispersed in polystyrene are reported as a function of temperature. For nanocomposites containing less than 0.1 wt% nanotubes, the enhancement of the magnitude of the complex modulus | E ∗ | = E ′ 2 + E ″ 2 , where E′ and E″ are the elastic and loss moduli, respectively, exceeded the predictions of the Halpin–Tsai model (this model is often used to predict the properties of macroscopic composites). In this concentration range, however, the loss tangent, tan δ = E″/ E′, of the nanocomposite remained comparable to that of pure PS, i.e., comparable elasticity. At larger concentrations the mechanical response became more elastic than PS, but the magnitude of the complex modulus fell appreciably below predictions based on the Halpin–Tsai model. An alternate hypothesis that relies on the role of attractive interactions between the nanotubes and polystyrene chains, and consistent with previous Raman scattering and glass transition temperature data, is proposed to describe the observed dynamic response.

The role of attractive interactions in rod-sphere mixtures.

We present a computer simulation study of binary mixtures of prolate Gay-Berne particles and Lennard-Jones spheres. Results are presented for three such rod-sphere systems which differ from each other only in the interaction between unlike particles. Both the mixing-demixing behavior and the transitions between the isotropic and any liquid crystalline phases are studied for each system, as a function of temperature and concentration ratio. For systems which show macroscopic demixing, the rod-sphere interaction is shown to give direct control over interfacial anchoring properties, giving rise to the possibility of micellar phase formation in the case of homeotropic anchoring. Additionally, it is shown that on incorporating high concentrations of spheres into a system of rods with weak demixing properties, microphase-separated structures can be induced, including bicontinuous and lamellar arrangements.

Role of attractive interactions on Bose-Einstein condensation.

The properties and stability of a trapped Bose-Einstein condensate are strongly influenced by attractive interactions between the particles. We describe the spatial distribution, stability, and collisional loss rates for a weakly interacting gas in the mean-field limit. We show how the condensate contracts and becomes unstable as the number of condensate atoms increases. We further show how the number of atoms is limited by the collisional loss rates associated with the contraction of the condensate; this loss is in addition to the particle ejection decay indentified by Kagan et al. \textcopyright{} 1996 The American Physical Society.

Role of attractive interactions in endo-exo stereoselectivities of Diels-Alder reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of attractive interactions in endo-exo stereoselectivities of Diels-Alder reactionsYoshiaki Kobuke, Takuji Sugimoto, Junji Furukawa, and Takayuki FuenoCite this: J. Am. Chem. Soc. 1972, 94, 10, 3633–3635Publication Date (Print):May 1, 1972Publication History Published online1 May 2002Published inissue 1 May 1972https://doi.org/10.1021/ja00765a066RIGHTS & PERMISSIONSArticle Views573Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (363 KB) Get e-Alerts Get e-Alerts