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arXiv 2202.02032cond-mat.soft
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二维活性布朗粒子系统中MIPS界面的内禀结构透视

Intrinsic structure perspective for MIPS interfaces in two dimensional systems of Active Brownian Particles

Enrique Chacon, Francisco Alarcon, Jorge Ramirez, Pedro Tarazona, Chantal Valeriani

摘要:

活性布朗粒子(ABP)的悬浮液在较宽的平均密度和活性强度范围内经历运动诱导相分离(MIPS)[1],即使在没有明确吸引力的情况下。据报道,从界面上的总作用力来看,机械表面张力为负值,而界面线的稳定波动将被解释为正毛细表面张力[2],而在平衡液体表面中,这两个量值相等。我们在这里提出的2D-ABP接口的固有密度和力的配置文件,计算与粒子的瞬时界面线的距离方面的分析。我们的研究结果提供了一个新的见解MIPS的起源从局部整流的随机作用力的颗粒附近的界面。正如已经指出的那样,该效应作为一种外部电势[3],在界面上产生压力梯度,因此MIPS的机械表面张力不能被描述为平衡共存相的机械张力;但我们的分析表明,大部分影响来自MIPS界面致密(内)侧的紧密笼状颗粒,而不是来自与致密团簇碰撞的外侧的自由移动粒子。此外,一个明确的相关性出现之间的衰减的六角序参量在致密板和结束的MIPS的强度的主动力降低。我们测试,与MIPS所需的强大的主动力,界面结构和性能是非常相似的ABP与纯排斥(WCA-LJ模型截断在其最小值),当相互作用包括一系列的LJ吸引力。

英文摘要:

Suspensions of Active Brownian Particles (ABP) undergo motility induced phase separation (MIPS) over a wide range of mean density and activity strength [1], even in the absence of an explicit attraction. Negative values of the mechanical surface tension have been reported, from the total forces across the interface, while the stable fluctuations of the interfacial line would be interpreted as a positive capillary surface tension [2], while in equilibrium liquid surfaces these two magnitudes are equal. We present here the analysis of 2D-ABP interfaces in terms of the intrinsic density and force profiles, calculated with the particle distance to the instantaneous interfacial line. Our results provide a new insight in the origin of the MIPS from the local rectification of the random active force on the particles near the interface. As it had been pointed, that effect acts as an external potential [3] that produces a pressure gradient across the interface, so that the mechanical surface tension of the MIPS cannot be described as that of equilibrium coexisting phases; but our analysis shows that most of that effect comes from the tightly caged particles at the dense (inner) side of the MIPS interface, rather than from the free moving particles at the outer side that collide with the dense cluster. Moreover, a clear correlation appears between the decay of the hexatic order parameter at the dense slab and the end of the MIPS as the strength of the active force is lowered. We test that with the strong active forces required for MIPS, the interfacial structure and properties are very similar for ABP with purely repulsive (WCA-LJ model truncated at its minimum) and when the interaction includes a range of the LJ attractive force.

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