The Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, Beijing 100029, PR China.
Langmuir. 2010 Jul 20;26(14):12190-7. doi: 10.1021/la100840a.
A systematic evaluation of the effect of polymer matrix molecular weight on the coarsening kinetics of uniformly dispersed polystyrene-grafted gold nanoparticles is presented. Particle coarsening is found to proceed via three stages (i.e., atomic-diffusion-based Ostwald ripening (OR), particle-migration-based collision-coalescence, and the subsequent reshaping of particle assemblies). The relative significance of each stage and hence the evolution of particle size and shape have been found to depend sensitively upon time, temperature, and the molecular weight of the host polymer. At temperatures close to the matrix glass-transition temperature, Ostwald ripening has been observed to be dominant on all experimental timescales. With increasing annealing temperature, collision coalescence becomes the dominant mode of coarsening, leading to rapid particle growth. The onset of the latter process is found to be increasingly delayed with increasing molecular weight of the polymer host. Particle coalescence is observed to proceed via two fundamental modes (i.e., diffusion-limited aggregation and growth resulting in the formation of fractal particle clusters and the subsequent recrystallization into more spherical monolithic aggregate structures). Interestingly, particle coarsening in high-molecular-weight matrix polymers is found to proceed significantly faster than predicted on the basis of the bulk polymer viscosity; this acceleration is interpreted to be a consequence of the network characteristics of high-molecular-weight polymers by analogy to the phenomenon of nanoviscosity that has been reported in the context of nanoparticle diffusion within high-molecular-weight polymers.
本文系统评估了聚合物基体分子量对均匀分散的聚苯乙烯接枝金纳米粒子粗化动力学的影响。研究发现，粒子粗化经历三个阶段（即基于原子扩散的奥斯特瓦尔德熟化（OR）、基于粒子迁移的碰撞-聚并以及随后的粒子组装再成形）。每个阶段的相对重要性以及粒子尺寸和形状的演化都高度依赖于时间、温度和基体聚合物的分子量。在接近基体玻璃化转变温度的温度下，在所有实验时间尺度上，奥斯特瓦尔德熟化都被观察到是主导的。随着退火温度的升高，碰撞聚并成为主要的粗化模式，导致粒子快速生长。后一过程的开始时间发现随着聚合物主链分子量的增加而逐渐延迟。粒子聚并被观察到通过两种基本模式进行（即扩散限制聚集和生长，导致形成分形粒子簇，随后再结晶成更球形的整体聚合体结构）。有趣的是，在高分子量基体聚合物中，粒子粗化的速度明显快于基于体相聚合物粘度的预测；这种加速可以通过高分子量聚合物的网络特性来解释，类似于在高分子量聚合物中纳米粒子扩散的情况下所报道的纳米粘度现象。
