Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi, India.
J Phys Chem B. 2012 Nov 1;116(43):13124-32. doi: 10.1021/jp307615f. Epub 2012 Oct 22.
Structural estimators for the entropy are combined with an analysis of the different contributions to the energy of solvation to understand the molecular basis of the thermodynamics of solvation of passivated nanoparticles. Molecular dynamics simulations of thiolated gold clusters in ethane are performed over a wide range of densities close to the critical isotherm. The entropic changes associated with solvent reorganization around the passivated nanoparticle are estimated from the nanoparticle-solvent pair correlation function, while the entropy of the ligand shell is estimated from the covariance in the positional fluctuations of the ligand atoms. The ligand-shell entropy (S(L)) is shown to be fairly insensitive to variations in solvent density ranging from vacuum to twice the critical density (ρ(c)). In contrast, the entropy change due to solvent reorganization (ΔS(ns)(ord)) shows a minimum around the critical point where the solvent excess shows a maximum. Combining the entropic estimates with the nanoparticle-solvent interaction energies, the free energy of solvation is shown to decrease with density once the critical point is crossed in a manner qualitatively consistent with available experimental data. The results suggest that such an approach to obtain structural insights into the thermodynamics of solvation of passivated nanoparticles could be useful in understanding the stability of nanoparticle dispersions of widely varying chemistries. This study also demonstrates that the theoretical analysis of solvation and self-assembly developed in the context of biomolecular hydration can be very usefully extended to understand the behavior of inorganic nanoparticle dispersions.
结构熵估计器与溶剂化能的不同贡献分析相结合，以理解纳米粒子钝化后的溶剂化热力学的分子基础。在接近临界等温线的广泛密度范围内，对乙烷中巯基化金团簇进行了分子动力学模拟。从钝化纳米粒子的溶剂化分子对相关函数中估计与溶剂重新排列相关的熵变，而配体壳的熵则从配体原子位置波动的协方差中估计。结果表明，配体壳熵（S（L））对溶剂密度从真空到临界密度（ρ（c））的两倍的变化相当不敏感。相比之下，由于溶剂重新排列引起的熵变（ΔS（ns）（ord））在临界点附近最小，此时溶剂过剩达到最大值。将熵估计与纳米粒子-溶剂相互作用能结合起来，表明一旦越过临界点，溶剂化自由能随密度降低，这种方式与可用的实验数据定性一致。结果表明，这种获得钝化纳米粒子溶剂化热力学结构见解的方法可能有助于理解具有广泛化学性质的纳米粒子分散体的稳定性。本研究还表明，在生物分子水合的背景下开发的溶剂化和自组装的理论分析可以非常有用地扩展，以理解无机纳米粒子分散体的行为。
