Wang Dongliang, Hore Michael J A, Ye Xingchen, Zheng Chen, Murray Christopher B, Composto Russell J
Department of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104, USA.
Soft Matter. 2014 May 21;10(19):3404-13. doi: 10.1039/c3sm52514g. Epub 2014 Mar 18.
The dispersion, local orientation and optical absorption of polystyrene (PS, degree of polymerization P) nanocomposites containing PS-grafted gold nanorods (Au NRs, PS degree of polymerization N), with aspect ratios (ν = length/diameter) ranging from 2.5 to 6.3, are studied using quantitative scanning electron microscopy (SEM) and optical spectroscopy. The experimentally observed nanorod assemblies and optical absorptions are compared with predictions from self-consistent field theory (SCFT) and finite difference time domain (FDTD) calculations, respectively. A pair correlation function for Au NRs is calculated from SEM images, and contains no correlation peaks for P/N = 0.9, indicating nanorods are dispersed within the nanocomposite. Large correlation peaks are observed for P/N = 7.6, representative of interparticle separation distances within nanorod aggregates, which do not vary with ν. On the basis of SCFT calculations, aggregation is attributed to significant depletion-attraction forces in the composite for P/N > 1. When Au NRs disperse, the longitudinal surface plasmon resonance (LSPR) peak red shifts from the visible into the near-IR as ν increases. No shift in the dispersed LSPR position is observed for v = 2.5 and 3.3 upon aggregation because the ratio of the interparticle distance to the nanorod length is too large for surface plasmon coupling. However, for v = 6.3, significant coupling between surface plasmons leads to a blue shift of the LSPR by approximately 140 nm, in agreement with FDTD calculations.
使用定量扫描电子显微镜（SEM）和光谱学研究了含有聚苯乙烯接枝金纳米棒（Au NRs，聚苯乙烯聚合度为N）的聚苯乙烯（PS，聚合度为P）纳米复合材料的分散性、局部取向和光吸收。所研究的纳米复合材料中纳米棒的长径比（ν = 长度/直径）范围为2.5至6.3。分别将实验观察到的纳米棒组装结构和光吸收与自洽场理论（SCFT）和时域有限差分（FDTD）计算的预测结果进行了比较。根据SEM图像计算了Au NRs的对关联函数，对于P/N = 0.9，该函数没有相关峰，这表明纳米棒分散在纳米复合材料中。对于P/N = 7.6，观察到较大的相关峰，这代表了纳米棒聚集体内的颗粒间分离距离，且该距离不随ν变化。基于SCFT计算，聚集归因于P/N > 1时复合材料中显著的耗尽吸引力。当Au NRs分散时，随着ν增加，纵向表面等离子体共振（LSPR）峰从可见光区域红移至近红外区域。对于v = 2.5和3.3，聚集时未观察到分散LSPR位置的移动，因为颗粒间距离与纳米棒长度的比值对于表面等离子体耦合来说太大。然而，对于v = 6.3，表面等离子体之间的显著耦合导致LSPR发生约140 nm的蓝移，这与FDTD计算结果一致。
