空间周期性外场作用下流体的相分离
Phase separation in fluids exposed to spatially periodic external fields
摘要：
我们考虑了空间周期性外场中流体的液-汽型相变。对于d=3维的流体，周期性场引起附加相位，其特征在于沿场方向的大密度调制。在三相点，所有三相（调制、蒸气和液体）共存。在略高于三相点的温度和低（高）值的化学势，调制相和蒸汽（液体）之间的两相共存观察。我们用计算机模拟和平均场论对伊辛模型研究了这一现象。理论表明，为了使调制相位出现，场波长必须超过阈值。我们还发现调制相和汽/液相之间的界面张力非常低。张力的量级为每平方晶格间距10^{-4} kB T，其中kB是玻耳兹曼常量，T是温度。为了检测这种低张力，提出了一种新的模拟方法。我们也考虑d=2维的情况。然后调制相位不存在，导致完全不同的相图。
英文摘要：
We consider the liquid-vapor type phase transition for fluids confined within spatially periodic external fields. For a fluid in d=3 dimensions, the periodic field induces an additional phase, characterized by large density modulations along the field direction. At the triple point, all three phases (modulated, vapor, and liquid) coexist. At temperatures slightly above the triple point and for low (high) values of the chemical potential, two-phase coexistence between the modulated phase and the vapor (liquid) is observed. We study this phenomenon using computer simulations and mean-field theory for the Ising model. The theory shows that, in order for the modulated phase to arise, the field wavelength must exceed a threshold value. We also find an extremely low tension of the interface between the modulated phase and the vapor/liquid phases. The tension is of the order 10^{-4} kB T per squared lattice spacing, where kB is the Boltzmann constant, and T the temperature. In order to detect such low tensions, a new simulation method is proposed. We also consider the case of d=2 dimensions. The modulated phase then does not survive, leading to a radically different phase diagram.
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