Phase behavior of colloidal superballs: Shape interpolation from spheres to cubes

被引:99
作者
Batten, Robert D. [2 ]
Stillinger, Frank H. [1 ]
Torquato, Salvatore [1 ,3 ,4 ,5 ,6 ,7 ]
机构
[1] Princeton Univ, Dept Chem, Princeton, NJ 08544 USA
[2] Princeton Univ, Dept Chem Engn, Princeton, NJ 08544 USA
[3] Princeton Univ, Dept Phys, Princeton, NJ 08544 USA
[4] Princeton Univ, Princeton Ctr Theoret Sci, Princeton, NJ 08544 USA
[5] Princeton Univ, Princeton Inst Sci & Technol Mat, Princeton, NJ 08544 USA
[6] Princeton Univ, Program Appl & Computat Math, Princeton, NJ 08544 USA
[7] Inst Adv Study, Sch Nat Sci, Princeton, NJ 08544 USA
来源
PHYSICAL REVIEW E | 2010年 / 81卷 / 06期
关键词
EQUATION-OF-STATE; MOLECULAR-DYNAMICS SIMULATION; NONSPHERICAL HARD PARTICLES; VIRIAL-COEFFICIENTS; DIAGRAM; SYSTEM; TRANSITION; ENTROPY; LIQUID; GOLD;
D O I
10.1103/PhysRevE.81.061105
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
The phase behavior of hard superballs is examined using molecular dynamics within a deformable periodic simulation box. A superball's interior is defined by the inequality vertical bar x vertical bar(2q)+vertical bar y vertical bar(2q)+vertical bar z vertical bar(2q) <= 1, which provides a versatile family of convex particles (q<0.5) with cubelike and octahedronlike shapes as well as concave particles (q<0.5) with octahedronlike shapes. Here, we consider the convex case with a deformation parameter q between the sphere point (q=1) and the cube (q=infinity). We find that the asphericity plays a significant role in the extent of cubatic ordering of both the liquid and crystal phases. Calculation of the first few virial coefficients shows that superballs that are visually similar to cubes can have low-density equations of state closer to spheres than to cubes. Dense liquids of superballs display cubatic orientational order that extends over several particle lengths only for large q. Along the ordered, high-density equation of state, superballs with 1 < q < 3 exhibit clear evidence of a phase transition from a crystal state to a state with reduced long-ranged orientational order upon the reduction of density. For q >= 3, long-ranged orientational order persists until the melting transition. The width of the apparent coexistence region between the liquid and ordered, high-density phase decreases with q up to q=4.0. The structures of the high-density phases are examined using certain order parameters, distribution functions, and orientational correlation functions. We also find that a fixed simulation cell induces artificial phase transitions that are out of equilibrium. Current fabrication techniques allow for the synthesis of colloidal superballs and thus the phase behavior of such systems can be investigated experimentally.
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页数:13
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