Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QZ, United Kingdom.
Langmuir. 2016 Dec 6;32(48):12716-12724. doi: 10.1021/acs.langmuir.6b02683. Epub 2016 Nov 23.
We investigate the segregation of impurities to grain boundaries in colloidal polycrystalline monolayers using video microscopy. A model colloidal alloy is prepared by embedding large spherical impurities in a polycrystalline monolayer of small host colloidal hard spheres, which stops grain growth at a finite grain size. The size ratio between the impurities and the host particles determines whether they behave as interstitial or substitutional impurities in the bulk crystal, akin to those in real alloys. We find that the partitioning of impurities between the grains and the grain boundaries is in very good agreement with the Langmuir-McLean adsorption model for equilibrium grain boundary segregation. This enables the direct measurement of the free energy of adsorption for the two types of impurities. Near saturation, we characterize the spatial distribution of the adsorbed impurities and find that it strongly depends on their interstitial or substitutional nature. This is because the relative importance of clustering and mixing due to nonadditivity is determined by geometrical constraints imposed by the crystalline host lattice.
我们使用视频显微镜研究胶体多晶单层中杂质向晶界的偏析。通过将大球形杂质嵌入小主体胶体硬球的多晶单层中来制备模型胶体合金，这会阻止晶粒在有限的晶粒尺寸下生长。杂质与主体颗粒之间的尺寸比决定了它们在体相晶体中作为间隙或替代杂质的行为，类似于真实合金中的情况。我们发现，杂质在晶粒和晶界之间的分配与平衡晶界偏析的 Langmuir-McLean 吸附模型非常吻合。这使得可以直接测量两种类型杂质的吸附自由能。在接近饱和时，我们表征了吸附杂质的空间分布，发现它强烈依赖于它们的间隙或替代性质。这是因为由于非加性引起的聚集和混合的相对重要性取决于晶体主体晶格施加的几何约束。
