Dipartimento di Fisica, Università di Bari, and INFN, Sezione di Bari, Via Amendola 173, 70126 Bari, Italy.
Philos Trans A Math Phys Eng Sci. 2011 Jun 28;369(1945):2592-9. doi: 10.1098/rsta.2011.0020.
Phase separation in a complex fluid with lamellar order has been studied in the case of cold thermal fronts propagating diffusively from external walls. The velocity hydrodynamic modes are taken into account by coupling the convection-diffusion equation for the order parameter to a generalized Navier-Stokes equation. The dynamical equations are simulated by implementing a hybrid method based on a lattice Boltzmann algorithm coupled to finite difference schemes. Simulations show that the ordering process occurs with morphologies depending on the speed of the thermal fronts or, equivalently, on the value of the thermal conductivity ξ. At large values of ξ, as in instantaneous quenching, the system is frozen in entangled configurations at high viscosity while it consists of grains with well-ordered lamellae at low viscosity. By decreasing the value of ξ, a regime with very ordered lamellae parallel to the thermal fronts is found. At very low values of ξ the preferred orientation is perpendicular to the walls in d=2, while perpendicular order is lost moving far from the walls in d=3.
层状有序复杂流体的相分离已在从外部墙壁扩散传播的冷热前沿的情况下进行了研究。通过将有序参数的对流-扩散方程与广义纳维-斯托克斯方程耦合，考虑了速度流体动力学模式。通过实施基于格子玻尔兹曼算法与有限差分方案相结合的混合方法对动力学方程进行了模拟。模拟表明，在热前沿速度或等效的热导率 ξ 的值的影响下，有序过程发生了具有形貌的变化。在 ξ 值较大的情况下，如瞬时淬火，系统在高粘度时被冻结在缠结状态，而在低粘度时则由具有良好层状的颗粒组成。通过降低 ξ 值，发现了与热前沿平行的非常有序的层状结构的区域。在 ξ 值非常低的情况下，在 d=2 中优先取向垂直于壁面，而在 d=3 中远离壁面时垂直有序则会丢失。
