Tiba Al A, Tivanski Alexei V, MacGillivray Leonard R
Department of Chemistry , University of Iowa , Iowa City , Iowa 52242-1294 United States.
Nano Lett. 2019 Sep 11;19(9):6140-6143. doi: 10.1021/acs.nanolett.9b02125. Epub 2019 Aug 27.
Size engineering is an emerging strategy to modulate the mechanical properties of crystalline materials. Herein, micro- and nanodimensional single crystals of the prototypical metal-organic framework (MOF) ZIF-8 are generated using solvothermal and solution methods, respectively. Atomic force microscopy-based nanoindentation technique was used to measure the Young's modulus values of micro- and nanodimensional individual ZIF-8 crystals. We demonstrate that crystal downsizing to nanoscale dimensions results in a 40% reduction in crystal stiffness. The change is attributed to a greater contribution of surface effects to the physical properties of nanocrystalline ZIF-8. The observed change in the mechanical properties may be used to explain reported size-dependent changes in gas adsorption of ZIF-8, thought to be a result of differences in framework flexibility at the nanoscale. Our work provides an important example on how downsizing of crystalline metal-organic materials can give rise to specific and tunable physical properties.
尺寸工程是一种调节晶体材料力学性能的新兴策略。在此，分别采用溶剂热法和溶液法制备了典型金属有机框架材料（MOF）ZIF-8的微米级和纳米级单晶。基于原子力显微镜的纳米压痕技术用于测量微米级和纳米级单个ZIF-8晶体的杨氏模量值。我们证明，将晶体尺寸缩小至纳米尺度会导致晶体刚度降低40%。这种变化归因于表面效应在纳米晶ZIF-8物理性质中占比更大。观察到的力学性能变化可用于解释ZIF-8气体吸附中报道的尺寸依赖性变化，这被认为是纳米尺度下框架柔韧性差异的结果。我们的工作为晶体金属有机材料尺寸缩小如何产生特定且可调节的物理性质提供了一个重要示例。
