Directed self-assembly of spherical caps via confinement
Directed self-assembly of spherical caps via confinement
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通过约束定向自组装球冠
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
F. Escobedo
中科院分区：
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作者：
C. Avendaño;C. M. L. Watson;F. Escobedo
本文采用蒙特卡罗模拟的方法研究了两个相距h的平行硬壁之间的球形帽的相行为。粒子模型由一个直径为σ的硬球组成，在高度χ处被平面切断，它松散地基于最近在实验中研究过的蘑菇帽状颗粒[E]。李建军，李建军，李建军，等。中国生物医学工程学报，2004,24(1):444 - 444。粒子的几何特征是高度χ* = χ/σ，使得模型在χ*→1的硬球和χ*→0的无限薄硬球帽之间外推。研究了三种不同的颗粒形状：(a)四分之三高度的球形帽（χ* =¾），(b)一半高度的球形帽或半球（χ* =½），以及(c)四分之一高度的球形帽（χ* =¼）。利用这三个模型对强约束条件下粒子形状对粒子熵驱动自组装的影响进行了合理化分析；即，对于1 < H/χ < 2.5。随着H的变化，观察到一系列的晶体结构，包括一些具有与在受限硬球中观察到的结构相似的对称性（由于颗粒中剩余的球面），但由于颗粒形状具有固有的各向异性和取向自由度而具有额外的特征。发现χ* = 3 / 4体系的相图与封闭蘑菇帽状胶体颗粒在封闭条件下的实验相图最为相似；然而，模拟还揭示了在接近给定h的紧密堆积条件时发生的其他六种相。构建了一个定性的全局相图，有助于揭示所研究的所有颗粒形状和约束下不同相之间的相互关系。
In this work we use Monte Carlo simulations to study the phase behavior of spherical caps confined between two parallel hard walls separated by a distance H. The particle model consists of a hard sphere of diameter σ cut off by a plane at a height χ, and it is loosely based on mushroom cap-shaped particles whose phase behavior was recently studied experimentally [E. K. Riley and C. M. Liddell, Langmuir, 26, 2010, 11648]. The geometry of the particles is characterized by the reduced height χ* = χ/σ, such that the model extrapolates between hard spheres for χ* → 1 and infinitely thin hard spherical caps for χ* → 0. Three different particle shapes are investigated: (a) three-quarter height spherical caps (χ* = ¾), (b) one-half height spherical caps or hemispheres (χ* = ½), and (c) one-quarter height spherical caps (χ* = ¼). These three models are used to rationalize the effect of particle shape on the entropy-driven self-assembly of the particles under strong confinements; i.e., for 1 < H/χ < 2.5. As H is varied, a sequence of crystal structures is observed, including some having similar symmetry as that of the structures observed in confined hard spheres on account of the remaining spherical surface in the particles, but with additional features on account of the particle shapes having intrinsic anisotropy and orientational degrees of freedom. The χ* = ¾ system is found to exhibit a phase diagram that is most similar to the one obtained experimentally for the confined mushroom cap-shaped colloidal particles under confinement; however, simulations also reveal six other phases that occur on approaching the close-packing conditions for a given H. A qualitative global phase diagram is constructed that helps reveal the interrelations among different phases for all the particle shapes and confinements studied.