Spinodal decomposition of a binary magnetic fluid confined to a surface

Abstract

In our previous work [J. Chem. Phys. 136, 024502 (2012)], we reported a demixing phase transition of a quasi-two-dimensional, binary Heisenberg fluid mixture driven by the ferromagnetic interactions of the magnetic species. Here, we present a theoretical study for the time-dependent coarsening occurring within the two-phase region in the density-concentration plane, also known as spinodal decomposition. Our investigations are based on dynamical density functional theory (DDFT). The particles in the mixture are modeled as Gaussian soft spheres on a two-dimensional surface, where one component carries a classical spin of Heisenberg type. To investigate the two-phase region, we first present a linear stability analysis with respect to small, harmonic density perturbations. Second, to capture nonlinear effects, we calculate time-dependent structure factors by combining DDFT with Percus' test particle method. For the growth of the average domain size l during spinodal decomposition with time t, we observe a power-law behavior l∝t^{δ_{α}} with δ_{m}≃0.333 for the magnetic species and δ_{n}≃0.323 for the nonmagnetic species.

Novel structure formation of a phase separating colloidal fluid in a ratchet potential

“…Experimentally, such systems involve, e.g., ferro-colloids and polymers [28]. In our model, the asymmetric interaction potentials yield (in two dimensions) a first-order demixing transition for a broad range of parameters, as we have already shown in earlier studies [29,30]. In the present letter we combine this interaction potential with a (one-dimensional) ratchet potential coupling to the spins.…”

“…For V ext m = 0, the system exhibits a first-order demixing transition accompanied by spinodal decomposition. This occurs in the region of the bulk phase diagram where the system is unstable against harmonic density perturbations with certain wave numbers |k| [30]. However, there is no favored direction for the demixing process.…”

“…However, we cannot exclude that the dynamical scaling law for the demixing might be influenced by L (see Ref. [30] for details). Moreover, the positioning of the stripes depends on the initial configuration which is given by the realization of the random white noise applied to the initial bulk profiles [29].…”

“…-Our model system consists of a binary mixture of Brownian particles confined to a two-dimensional substrate, where one species is magnetic (m) and the other one is non-magnetic (n) [29,30] (for an experimental counterpart see, e.g., Ref. [28]).…”

Моделирование Распада Бинарных Сплавов На Основе Метода Функционала Плотности Свободной Энергии

“…Одним из основных уравнений для моделей такого типа яв-ляется уравнение Кана-Хилларда [5][6][7], которое, как правило, применяется (с учетом различных модифи-каций) для описания процесса формирования фаз в области спинодального распада (см., например, [8][9][10]). Использование данного уравнения для описания про-цесса нуклеации также является весьма эффективным (см., например, [11,12]), поскольку позволяет рассмат-ривать кластеры, имеющие переменный состав и ха-рактеризующиеся протяженной областью сопряжения фаз и переменным поверхностным натяжением.…”