纳米尺度表面间配体介导的相互作用对温度、小面尺寸和配体覆盖率的敏感性和非线性依赖性
Ligand-Mediated Interactions between Nanoscale Surfaces Depend Sensitively and Nonlinearly on Temperature, Facet Dimensions, and Ligand Coverage
摘要：
纳米粒子通常被覆盖在配体单层中，配体单层可以经历温度依赖性的有序-无序转变，该转变将溶液中的粒子-粒子相互作用从排斥转变为吸引。在这项工作中，我们研究如何在配体的表面覆盖度和刻面尺寸的变化影响配体的排序，附近的溶剂分子的排列，以及不同的粒子上的配体单层之间的相互作用。特别是，我们考虑的情况下，强烈结合的十八烷基配体的（100）方面的CdS在存在下的明确的正己烷溶剂。根据小平面尺寸和表面覆盖率，我们观察到三个不同的有序状态，不同的配体是如何包装在一起，并影响配体壳层的厚度和配体-溶剂界面的结构。当从上面接近纳米尺度时，有序-无序转变的温度依赖性也以非线性的方式变宽并向较低的温度移动。我们发现，在纳米尺度的小平面上的配体可以表现得非常相似的宏观表面上的溶液中，和一些小平面的尺寸影响配体排列比其他更强烈。随着配体的有序化，相对单层之间的相互作用变得有吸引力，甚至远低于完全表面覆盖。每单位表面积的吸引力的强度是强烈的配体覆盖率的影响，但只有微弱的小面宽度。相反，我们发现，使两个单分子膜在一起的有序-无序转变温度以上可以诱导有序和吸引力。
英文摘要：
Nanoparticles are often covered in ligand monolayers, which can undergo a temperature-dependent order-disorder transition that switches the particle-particle interaction from repulsive to attractive in solution. In this work, we examine how changes in the ligand surface coverage and facet dimensions affect the ordering of ligands, the arrangement of nearby solvent molecules, and the interaction between ligand monolayers on different particles. In particular, we consider the case of strongly bound octadecyl ligands on the (100) facet of CdS in the presence of an explicit n-hexane solvent. Depending on the facet dimensions and surface coverage, we observe three distinct ordered states that differ in how the ligands are packed together, and which affect the thickness of the ligand shell and the structure of the ligand-solvent interface. The temperature dependence of the order-disorder transition also broadens and shifts to lower temperature in a nonlinear manner as the nanoscale is approached from above. We find that ligands on nanoscale facets can behave very similarly to those on macroscopic surfaces in solution, and that some facet dimensions affect the ligand alignment more strongly than others. As the ligands order, the interaction between opposing monolayers becomes attractive, even well below full surface coverage. The strength of attraction per unit surface area is strongly affected by ligand coverage, but only weakly by facet width. Conversely, we find that bringing two monolayers together just above the order-disorder transition temperature can induce ordering and attraction.
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