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European Physical Journal. E, Soft Matter

Carl A Whitfield, Tapan Chandra Adhyapak, Adriano Tiribocchi, Gareth P Alexander, Davide Marenduzzo, Sriram Ramaswamy
We describe the basic properties and consequences of introducing active stresses, with principal direction along the local director, in cholesteric liquid crystals. The helical ground state is found to be linearly unstable to extensile stresses, without threshold in the limit of infinite system size, whereas contractile stresses are hydrodynamically screened by the cholesteric elasticity to give a finite threshold. This is confirmed numerically and the non-linear consequences of instability, in both extensile and contractile cases, are studied...
April 2017: European Physical Journal. E, Soft Matter
Dimitri Mutschler, Mohamed Aziz Larabi, Abdelkader Mojtabi
The aim of this work is to present a theoretical analysis of the separation of an N-component mixture. In this study, two analytical models explaining the thermo-gravitational separation of components in N-component mixtures for vertical cavity filled by a porous medium are presented and assessed. The basic state and the separation are expressed in terms of the separation ratio, and the Lewis, cross-diffusion and Rayleigh numbers. Our computational analysis confirms that, for the given values of the mass fractions, thermodiffusion can be measured with a thermo-gravitational column, strongly supporting the experimentally determined transport coefficients...
April 2017: European Physical Journal. E, Soft Matter
Carlindo Vitoriano
We generalize the Ericksen-Leslie theory for the dynamics of nematic liquid crystals by including the director-density coupling energy [Formula: see text]. It corresponds to the cost in energy due to the interaction of spatially varying mass density [Formula: see text] and the liquid crystal director [Formula: see text]. A striking confirmation of the theory is achieved by confronting it with experimental data on acoustical Fréedericksz transition.
April 2017: European Physical Journal. E, Soft Matter
Yu A Budkov, N N Kalikin, A L Kolesnikov
We present a simple analytical theory of a flexible polymer chain dissolved in a good solvent, carrying permanent freely oriented dipoles on the monomers. We take into account the dipole correlations within the random phase approximation (RPA), as well as a dielectric heterogeneity in the internal polymer volume relative to the bulk solution. We demonstrate that the dipole correlations of monomers can be taken into account as pairwise ones only when the polymer chain is in a coil conformation. In this case the dipole correlations manifest themselves through the Keesom interactions of the permanent dipoles...
April 2017: European Physical Journal. E, Soft Matter
Andrew M Reynolds, Michael Sinhuber, Nicholas T Ouellette
Midge swarms are a canonical example of collective animal behaviour where local interactions do not clearly play a major role and yet the animals display group-level cohesion. The midges appear somewhat paradoxically to be tightly bound to the swarm whilst at the same time weakly coupled inside it. The microscopic origins of this behaviour have remained elusive. Models based on Newtonian gravity do, however, agree well with experimental observations of laboratory swarms. They are biologically plausible since gravitational interactions have similitude with long-range acoustic and visual interactions, and they correctly predict that individual attraction to the swarm centre increases linearly with distance from the swarm centre...
April 2017: European Physical Journal. E, Soft Matter
I Kriuchevskyi, J P Wittmer, O Benzerara, H Meyer, J Baschnagel
Focusing on simulated polymer glasses well below the glass transition, we confirm the validity and the efficiency of the recently proposed simple-average expression [Formula: see text] for the computational determination of the shear stress relaxation modulus G(t). Here, [Formula: see text] characterizes the affine shear transformation of the system at t = 0 and h(t) the mean-square displacement of the instantaneous shear stress as a function of time t. This relation is seen to be particulary useful for systems with quenched or sluggish transient shear stresses which necessarily arise below the glass transition...
April 2017: European Physical Journal. E, Soft Matter
Thomas Le Goff, Tung B T To, Olivier Pierre-Louis
We have modeled the nonlinear dynamics and the rheological behavior of a system under shear containing a membrane confined between two attractive walls. The presence of the membrane induces additional tangential forces on the walls that always increase the global friction. At low shear rates, the membrane exhibits chaotic dynamics with slow coarsening leading to thixotropy, i.e. to a slow decrease of the membrane-induced tangential forces on the walls. At intermediate shear rates, the membrane profile presents stationary periodic patterns...
April 2017: European Physical Journal. E, Soft Matter
Jorge González-Gutiérrez, J C Ruiz-Suárez
Few years ago an article addressing the physics behind aaabstract paintings was published by Herczyński et al. (Phys. Today 64, 31 (2011) issue No. 6). The authors aimed to understand how artists like Jackson Pollock manipulated paints to create pieces of art where the theory of fluid dynamics had a clear and perceivable role. Scaling laws were found to explain the plasticity observed in the artists's traces that we admire in worldwide museums. Because sand drawings are not only wonderful artistic expressions but also intangible cultural heritages of humanity, we wonder if they could be analyzed in a similar fashion...
April 2017: European Physical Journal. E, Soft Matter
M N Popescu, W E Uspal, M Tasinkevych, S Dietrich
Colloids can achieve motility by promoting at their surfaces chemical reactions in the surrounding solution. A well-studied case is that of self-phoresis, in which motility arises due to the spatial inhomogeneities in the chemical composition of the solution and the distinct interactions of the solvent molecules and of the reaction products with the colloid. For simple models of such chemically active colloids, the steady-state motion in an unbounded solution can be derived analytically in closed form. In contrast, for such chemically active particles moving in the vicinity of walls, the derivation of closed-form and physically intuitive solutions of the equations governing their dynamics turns out to be a severe challenge even for simple models...
April 2017: European Physical Journal. E, Soft Matter
Rouhollah Haji Abdolvahab
Chaperones are binding proteins working as a driving force in biopolymer translocation. They bind to the biopolymer near the pore and prevent its backsliding. Chaperones may have different spatial distributions. Recently, we showed the importance of their spatial distribution in translocation and its effects on the sequence dependency of the translocation time. Here we focus on homopolymers and exponential distribution. Because of the exponential distribution of chaperones, the energy dependency of the translocation time will change...
April 2017: European Physical Journal. E, Soft Matter
Cecília I A V Santos, Valentina Shevtsova, Ana C F Ribeiro
The Taylor dispersion technique has been used for measuring ternary mutual diffusion coefficients for mixtures of cyclohexane-toluene-methanol, corresponding to the mixtures under study on the International Space Station (ISS) within the scope of the project DCMIX2 (second series of the experiment Diffusion Coefficients in Mixtures). Five ternary systems with different composition of cyclohexane-toluene-methanol were investigated in order to accurately obtain the mass diffusion coefficients, contributing to a better understanding of the isothermal molecular diffusion in conjunction with the coupled flows of solutes occurring in such fluid systems...
April 2017: European Physical Journal. E, Soft Matter
S Ashraf, G Visavale, S S Bahga, J Phirani
The imbibition of a wetting fluid in a homogeneous porous medium follows the diffusion-like behavior described by Washburn. The impregnation of a two-layered porous medium by a wetting fluid due to capillary action has been previously described to have two fronts, one saturating the medium and the other, leading front, which propagates in finer pores. Here, we report that the leading front is governed by the porous structure and is not always in the finer pores. Based on the experiments in a layered porous medium of permeability varying perpendicular to the direction of flow, we show that the permeability of the adjacent layers plays a significant role in determining the leading front amongst the layers...
April 2017: European Physical Journal. E, Soft Matter
Soumaya Ouadhani, Ali Abdennadher, Abdelkader Mojtabi
The authors studied the effect of vertical high-frequency and small-amplitude vibrations on the separation of a binary mixture saturating a porous cavity. The horizontal bottom plate was submitted to constant uniform heat flux and the top one was maintained at constant temperature while no mass flux was imposed. The influence of vertical vibrations on the onset of convection and on the stability of the unicellular flow was investigated for positive separation ratio [Formula: see text]. The case of high-frequency and small-amplitude vibrations was considered so that a formulation using time averaged equations could be used...
April 2017: European Physical Journal. E, Soft Matter
Emine Kemiklioglu, Liang-Chy Chien
We have reported polymer-dispersed blue-phase (PDBP) liquid-crystal films via polymerization-induced phase separation. PDBP films are prepared by photochemical polymerization of curable crosslinking agent, monomer and blue-phase liquid crystal under an ultraviolet (UV) light. The influences of photoinitiator and weight ratio between monomer/crosslinking agent and blue phase on the electro-optical properties of PDBP liquid-crystal samples are investigated. The electro-optical (E-O) properties of PDBP films are determined in the top-down electro-optical cell...
April 2017: European Physical Journal. E, Soft Matter
Ion Lizarraga, Fabrizio Croccolo, Henri Bataller, M Mounir Bou-Ali
In the present work, the Soret coefficient has been determined at high pressure for a binary hydrocarbon mixture by combining the thermogravitational column and the dynamic near-field imaging techniques. The analyzed mixture is an iso-massic n -dodecane-n -hexane mixture at 298.15K. The molecular diffusion coefficient has been measured up to 20MPa by means of the dynamic analysis of the light scattered by non-equilibrium concentration fluctuations. With a cylindrical thermogravitational column the thermodiffusion coefficient was determined from 0...
March 2017: European Physical Journal. E, Soft Matter
Henri Bataller, Thomas Triller, Bastian Pur, Werner Köhler, José Maria Ortiz de Zárate, Fabrizio Croccolo
Dynamic analysis of the light scattered by non-equilibrium fluctuations in a thermodiffusion experiment has been performed on a sample of polystyrene-toluene-n -hexane, at 0.9-49.55-49.55% mass fraction. Time decays of the non-equilibrium fluctuations have been obtained revealing the accurate detectability of three modes. The slowest mode has been attributed to the mass diffusion of the polymer into the binary solvent; the intermediate one to mass diffusion of the two molecular components of the solvent; finally, the fastest one has been attributed to the thermal diffusivity of the overall mixture...
March 2017: European Physical Journal. E, Soft Matter
Helmut R Brand, Harald Pleiner
We investigate the influence of transient or permanent elasticity on liquid phases with octupolar (tetrahedral) order, a question that has never been addressed before. The focus will be on optically isotropic liquid phases with tetrahedral order including the T d phase and the chiral T phase introduced by Fel. It turns out that the presence of both, a network as well as tetrahedral order can lead to the formation of chiral domains of both hands in an optically isotropic fluid due to a completely novel mechanism, thus providing a possible macroscopic explanation for recent experimental observations...
March 2017: European Physical Journal. E, Soft Matter
Daniel L Z Caetano, Sidney J de Carvalho
Polyampholytes are polymers that have positive and negative monomers along their chain. The adsorption of polyampholytes on charged surfaces has been the subject of a large number of theoretical, computational and experimental studies due to its importance in a variety of bio and nanothechnological systems. However, computational studies focusing on interaction between polyampholytes and cylindrical charged surfaces are rather scarce. This study, therefore, aims to investigate the conformational properties of block-polyampholytes in the presence of a negatively charged cylinder by means of Metropolis Monte Carlo simulations...
March 2017: European Physical Journal. E, Soft Matter
A G Hansen, N Ramakrishnan, P B Sunil Kumar, J H Ipsen
The properties of self-avoiding p-atic membranes restricted to spherical topology have been studied by Monte Carlo simulations of a triangulated random surface model. Spherically shaped p-atic membranes undergo a Kosterlitz-Thouless transition as expected with topology induced mutually repelling disclinations of the p-atic ordered phase. For flexible membranes the phase behaviour bears some resemblance to the spherically shaped case with a p-atic disordered crumpled phase and p-atic ordered, conformationally ordered (crinkled) phase separated by a KT-like transition with proliferation of disclinations...
March 2017: European Physical Journal. E, Soft Matter
Erfan Kadivar, Atefeh Alizadeh
Motivated by a recent experiment (C. Ulloa et al., Phys. Rev. E 89, 033004 (2014)), droplet deformation in a flat microfluidic channel having a cross intersection with two inlet channels and two outlet channels, i.e. hyperbolic flow, is numerically investigated. Employing the boundary element method (BEM), we numerically solve the Darcy equation in the two dimensions and investigate droplet motion and droplet deformation as the droplet enters the cross intersection. We numerically find that the maximum deformation of droplet depends on droplet size, capillary number, viscosity ratio and flow rate ratio of the two inlets...
March 2017: European Physical Journal. E, Soft Matter
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