Stabilization mechanisms of nonpolar metal colloids with thin organic shells

非极性纳米粒子是一类重要的胶体。近二十年来发展起来的合成方法产生了金、银、铜和其他金属和半导体的颗粒。它们的核被有机配体覆盖，使它们可分散在烷烃、芳烃和其他非极性溶剂中。这些粒子是不带电的，不稳定的库仑排斥。然而，来自申请人和其他研究小组的最近结果表明，金属核、配体和溶剂的某些组合导致出乎意料地大的胶体稳定性。结果表明，稳定性是由于壳的分子结构。这与DLVO理论中描述的传统水胶体形成鲜明对比，我们提出具有薄有机壳的非极性金属胶体的稳定化机制有三种，它们是：无序配体壳的熵贡献，有机壳被分子水平上强烈相互作用的溶剂溶剂化，有机壳被分子水平上强烈相互作用的溶剂化，有机壳被分子水平上强烈相互作用的溶剂化，有机壳被分子水平上强烈相互作用的溶剂化，有机壳被分子水平上强烈相互作用的溶剂化。以及溶质分子在配体壳层中的嵌入提供协同稳定性。本项目使用核直径为1-10 nm的金胶体研究所提出的机制。系统系列是化学合成的，覆盖着强烈结合的直链、支链或扭结（不饱和）烃链。将所得胶体仔细纯化并转移到不同的溶剂和溶剂混合物中。颗粒的结构--特别是壳的密度及其构型--可进行定量评估。胶体稳定性或分散体可通过一种新技术进行定量分析，该技术是在小角X射线散射过程中胶体液滴缓慢蒸发的方法。监测颗粒浓度和团聚状态。热稳定性的测量使用温度依赖的X射线和动态光散射实验。使用热重分析法、拉曼光谱法、核磁共振、光散射和X射线散射的组合分析分子壳结构。所有实验结果与澳大利亚悉尼Asaph Widmer-Cooper博士小组提供的详细分子动力学模拟进行比较。它们在两个小组之前的合作中得到了改进，现在将用于测试纳米颗粒稳定化的拟议机制。

Nonpolar nanoparticles are an important class of colloids. Syntheses developed in the last two decades yield particles of gold, silver, copper, and other metals and semiconductors. Their cores are covered with organic ligands that render them dispersible in alkanes, aromatics, and other nonpolar solvents. These particles are uncharged and not stabilized by Coulomb repulsion. Recent results from the applicant and other research groups demonstrate, however, that certain combinations of metal core, ligand, and solvent lead to unexpectedly great colloidal stabilities. The results indicate that the stability is due to the molecular structure of the shell. This is in stark contrast to conventional aqueous colloids that are described in DLVO theory.We propose here that nonpolar metal colloids with thin organic shells are stabilized by three mechanisms that have not yet been studied systematically: the entropic contributions of disordered ligand shells; the solvation of the organic shells by solvents that strongly interact on a molecular level; and the intercalation of solute molecules in the ligand shell that provide synergistic stability.This project investigates the proposed mechanisms using gold colloids with core diameters of 1-10 nm. Systematic series are chemically synthesized and covered with strongly bound linear, branched, or kinked (unsaturated) hydrocarbon chains. The resulting colloids are carefully purified and transferred to different solvents and solvent mixtures. The structure of the particles - in particular the density of the shell and its configuration - is assessed quantitatively.The colloidal stability or the dispersions is quantified as a function of concentration using a new technique where a droplet of colloid slowly evaporates during Small-Angle X-ray Scattering. Both particle concentration and agglomeration state are monitored. Thermal stability is measured using temperature-dependent X-ray and dynamic light scattering experiments. The molecular shell structure is analyzed using a combination of thermogravimetry, Raman spectrometry, NMR, optical scattering, and X-ray scattering.All experimental results are compared to detailed Molecular Dynamic simulations that are available in the group of Dr. Asaph Widmer-Cooper in Sydney, Australia. They were refined in previous collaborations between the two groups and will now be used to test the proposed mechanisms of nanoparticle stabilization.