arXiv subjects

M. -Carmen Miguel

Publications and source records attributed to M. -Carmen Miguel.

21 records · Page 2Linked to original sources

arXiv1998

A field-oriented chain of dipolar particles in elongational flow

We study the behavior of an isolated field-oriented chain of dipolar particles in elongational fluid flow. Our main goal is to emphasize the effect of dipolar interactions on the chain's contribution to the pressure tensor and to the viscosities of a dilute suspension of these linear aggregates. In our model, despite the overall rigid appearance of the chain at rest, the constituent beads may move slightly relative to one another, conferring a certain degree of flexibility to the chain. This flexibility is quantified in terms of a dimensionless parameter, $λ^{-1}$, comparing thermal and dipolar energies. We perform an expansion in $λ^{-1}$, and obtain the first correction to the rigid chain contribution to the Kramers' pressure tensor for different flow geometries. The interplay of the elongational flow field and the field-induced chain orientation gives rise to a rich variety of scenarios. We compute the elongational, shear, and rotational viscosities in some representative situations.

cond-mat.soft↗

arXiv1998

Kinetic growth of field-oriented chains in dipolar colloidal solutions

Experimental studies on the irreversible growth of field-induced chains of dipolar particles suggest an asymptotic power-law behavior of several relevant quantities. We introduce a Monte Carlo model of chain growth that explicitly incorporates the anisotropic diffusion characteristic of a rod-like object. Assuming a simple power-law form for the mean cluster size, $S(t) \sim t^z$, the results of our model are in good agreement with the experimental measurements of the dynamic exponent $z$. Nevertheless, an alternative scenario, including logarithmic corrections to the standard power-law behavior, provides a better and more insightful interpretation of the anomalous dynamic exponent. In contrast to some experimental findings, we do not observe any dependence of the exponents on the volume fraction of particles $ϕ$. Finite-size effects are also explored by simulating very long time evolutions or highly concentrated systems. Two different behaviors are found, namely, saturation and a crossover to a quasi one-dimensional regime.

cond-mat.stat-mech↗

arXiv1997

Threading dislocation lines in two-sided flux array decorations

Two-sided flux decoration experiments indicate that threading dislocation lines (TDLs), which cross the entire film, are sometimes trapped in metastable states. We calculate the elastic energy associated with the meanderings of a TDL. The TDL behaves as an anisotropic and dispersive string with thermal fluctuations largely along its Burger's vector. These fluctuations also modify the structure factor of the vortex solid. Both effects can in principle be used to estimate the elastic moduli of the material.

cond-mat.supr-con↗