Stover Robert J, Moaseri Ehsan, Gourisankar Sai P, Iqbal Muhammad, Rahbar Negin K, Changalvaie Behzad, Truskett Thomas M, Johnston Keith P
Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
Langmuir. 2016 Feb 2;32(4):1127-38. doi: 10.1021/acs.langmuir.5b03639. Epub 2016 Jan 25.
The self-assembly of citrate-capped Au nanoparticles (5 nm) resulted in branched nanochains by adding CaCl2 versus spherical nanoclusters for NaCl. These assemblies were formed between 1 s to 30 min by tuning the electrostatic repulsion and the interparticle bridging attraction between the cations and citrate ligands as a function of electrolyte concentration. For dilute Ca(2+), strong interparticle bridging favored particle attachment at chain ends. This resulted in the formation of small, branched chains with lengths as short as 20 nm, due to the large Debye length for the diffuse counterions. Furthermore, the bridging produced very small interparticle spacings and sintering, as evident in high-resolution TEM despite the low temperature. This morphology produced a large red shift in the surface plasmon resonance, as characterized by a broad extinction peak with NIR absorption out to 1000 nm, which is unusual for such small particles. Whereas these properties were seen for primary particles with partial citrate monolayers, the degrees of sintering and NIR extinction were small in the case of citrate multilayers. The ability to design the size and shape of nanoparticle clusters as well as the interparticle spacing by tuning bridging and electrostatic interactions may be expected to be quite general and of broad applicability in materials synthesis.
通过添加氯化钙，柠檬酸盐包覆的金纳米颗粒（5纳米）自组装形成了分支纳米链，而添加氯化钠则形成球形纳米团簇。通过调节阳离子与柠檬酸盐配体之间的静电排斥和粒子间桥连吸引力（作为电解质浓度的函数），在1秒到30分钟内形成了这些组装体。对于稀的Ca(2+)，强粒子间桥连有利于粒子在链端附着。由于扩散反离子的德拜长度较大，这导致形成长度短至20纳米的小分支链。此外，尽管温度较低，但高分辨率透射电镜显示，桥连产生了非常小的粒子间间距和烧结。这种形态在表面等离子体共振中产生了很大的红移，其特征是具有近红外吸收直至1000纳米的宽消光峰，这对于如此小的粒子来说是不寻常的。虽然在具有部分柠檬酸盐单层的初级粒子中观察到了这些性质，但在柠檬酸盐多层的情况下，烧结程度和近红外消光较小。通过调节桥连和静电相互作用来设计纳米颗粒簇的尺寸和形状以及粒子间间距的能力，有望具有相当的普遍性，并在材料合成中具有广泛的适用性。
