Search results for "Condensed Matter::Soft Condensed Matter"
showing 10 items of 716 documents
Isotropic-nematic interface in suspensions of hard rods: Mean-field properties and capillary waves
2006
We present a study of the isotropic-nematic interface in a system of hard spherocylinders. First we compare results from Monte Carlo simulations and Onsager density functional theory for the interfacial profiles of the orientational order parameter and the density. Those interfacial properties that are not affected by capillary waves are in good agreement, despite the fact that Onsager theory overestimates the coexistence densities. Then we show results of a Monte Carlo study of the capillary waves of the interface. In agreement with recent theoretical investigations (Eur.Phys.J. E {\bf 18} 407 (2005)) we find a strongly anistropic capillary wave spectrum. For the wave-numbers accessed in o…
Capillary Waves in a Colloid-Polymer Interface
2004
The structure and the statistical fluctuations of interfaces between coexisting phases in the Asakura-Oosawa (AO) model for a colloid--polymer mixture are analyzed by extensive Monte Carlo simulations. We make use of a recently developed grand canonical cluster move with an additional constraint stabilizing the existence of two interfaces in the (rectangular) box that is simulated. Choosing very large systems, of size LxLxD with L=60 and D=120, measured in units of the colloid radius, the spectrum of capillary wave-type interfacial excitations is analyzed in detail. The local position of the interface is defined in terms of a (local) Gibbs surface concept. For small wavevectors capillary wa…
Effects of finite thickness on interfacial widths in confined thin films of coexisting phases
1999
The capillary broadening of a 2-phase interface is investigated both experimentally and theoretically. When a binary mixture in a thin film with thickness D segregates into two coexisting phases the interface between the two phases may form parallel to the substrate due to preferential surface attraction of one of the components. We show that the interfacial profile (of intrinsic width w0) is broadened due to capillary waves, which lead to fluctuations, of correlation length of the local interface positions in the directions parallel to the confining walls. We postulate that acts as an upper cutoff for the spectrum of capillary waves on the interface, so that the effective mean square inter…
Salt-induced microheterogeneities in binary liquid mixtures
2017
The salt-induced microheterogeneity (MH) formation in binary liquid mixtures is studied by small-angle x-ray scattering (SAXS) and liquid state theory. Previous experiments have shown that this phenomenon occurs for antagonistic salts, whose cations and anions prefer different components of the solvent mixture. However, so far the precise mechanism leading to the characteristic length scale of MHs has remained unclear. Here, it is shown that MHs can be generated by the competition of short-ranged interactions and long-ranged monopole-dipole interactions. The experimental SAXS patterns can be reproduced quantitatively by fitting to the derived correlation functions without assuming any speci…
Computer simulation of bottle-brush polymers with flexible backbone: good solvent versus theta solvent conditions.
2011
By Molecular Dynamics simulation of a coarse-grained bead-spring type model for a cylindrical molecular brush with a backbone chain of $N_b$ effective monomers to which with grafting density $\sigma$ side chains with $N$ effective monomers are tethered, several characteristic length scales are studied for variable solvent quality. Side chain lengths are in the range $5 \le N \le 40$, backbone chain lengths are in the range $50 \le N_b \le 200$, and we perform a comparison to results for the bond fluctuation model on the simple cubic lattice (for which much longer chains are accessible, $N_b \le 1027$, and which corresponds to an athermal, very good, solvent). We obtain linear dimensions of …
Simultaneous measurement of rotational and translational diffusion by forced Rayleigh scattering. Colloid spheres in suspension
1996
Abstract It is shown that the technique of forced Rayleigh scattering, traditionallyemployed to probe translational diffusion, can be employed to probe rotational diffusion as well. Thus with a single experiment both quantities are measured. The system under investigation is colloid spheres suspended in a glass-forming liquid. Furthermore, it is shown that the Stokes-Einstein and Debye-Stokes-Einstein relations for translational and rotational diffusion, respectively, are valid for spherical colloid particles in a supercooled liquid matrix in the vicinity of the glassy state.
Hydrodynamics of a co-current three-phase solid-bed reactor for foaming systems
2001
The objective of the present study was to evaluate the parameters, which characterize the pulsing flow of the gas and liquid through a bed, namely the frequency of pulsation, the velocity of the pulses and the pulse structure, for foaming systems. The paper presents the results of experiments aimed at determining the effect of the foaming power and the surface tension of liquid phase on the values of the measured parameters.
Size Dependence of Tracer Diffusion in Supercooled Liquids
1996
We have determined by forced Rayleigh scattering the diffusion coefficients D of several photochromic tracers with van der Waals radii between 0.38 and 8 nm (the largest ones being photolabeled polystyrene micronetworks) in 10 glass-forming liquids at temperatures between the glass temperature Tg and ∼1.2Tg. The results were analyzed in terms of power law plots, D(T) ∝ T/η(T)ξ, where η is the solvent shear viscosity, and temperature shifts, D(T) ∝ T/η(T + ΔT). The shift ΔT was related with the width of the rotational correlation time distribution via the time−temperature superposition principle.
On the electrophoretic mobility of isolated colloidal spheres
2004
We studied the electrophoretic mobility μ of highly charged colloidal spheres in very dilute low salt aqueous suspension. We combined experiments on individual particles and ensemble averaged measurements. In both cases μ was observed to be independent of particle size and surface chemistry. Corresponding effective charges Zμ*, however, scaled with the ratio of particle size to Bjerrum length λB: Zμ* = Aa/λB with a coefficient . Our results are discussed in comparison to other charge determination experiments and charge renormalization theory and with respect to the issue of charge polydispersity.
Charged particles at fluid interfaces as a probe into structural details of a double layer
2011
Electrostatic interactions between charged, distant colloids in a bulk electrolyte solution do not depend on the inherent structure of ions and a solvent forming a double layer. For charged colloids trapped at an interface between an electrolyte and air this no longer holds; as the electrostatic interactions are mediated via air and the field lines determining the interactions originate at the charged surface, these details come into prominence. Using the Langevin-Poisson-Boltzmann equation we investigate how steric effects and the polarization saturation of a solvent effect the contact potential at the colloid surface and, in consequence, the long range interactions between colloids trappe…