Department of Chemical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
ACS Nano. 2016 May 24;10(5):5260-71. doi: 10.1021/acsnano.6b01050. Epub 2016 Apr 25.
Crystals self-assembled from nanoparticles have useful properties such as optical activity and sensing capability. During fabrication, however, gelation and glassification often leave these materials arrested in defective or disordered metastable states. This is a key difficulty preventing adoption of self-assembled nanoparticle materials at scale. Processes which suppress kinetic arrest and defect formation while accelerating growth of ordered materials are essential for bottom-up approaches to creating nanomaterials. Dynamic, directed self-assembly processes in which the interactions between self-assembling components are actuated temporally offer one promising methodology for accelerating and controlling bottom-up growth of nanostructures. In this article, we show through simulation and theory how time-dependent, periodically toggled interparticle attractions can avoid kinetic barriers and yield well-ordered crystalline domains for a dispersion of nanoparticles interacting via a short-ranged, isotropic potential. The growth mechanism and terminal structure of the dispersion are controlled by parameters of the toggling protocol. This control allows for selection of processes that yield rapid self-assembled, low defect crystals. Although self-assembly via periodically toggled attractions is inherently unsteady and out-of-equilibrium, its outcome is predicted by a first-principles theory of nonequilibrium thermodynamics. The theory necessitates equality of the time average of pressure and chemical potential in coexisting phases of the dispersion. These quantities are evaluated using well known equations of state. The phase behavior predicted by this theory agrees well with measurements made in Brownian dynamics simulations of sedimentation equilibrium and homogeneous nucleation. The theory can easily be extended to model dynamic self-assembly directed by other toggled conservative force fields.
由纳米粒子自组装而成的晶体具有光学活性和传感能力等有用性质。然而，在制造过程中，凝胶化和玻璃化经常导致这些材料被困在有缺陷或无序的亚稳状态中。这是阻止自组装纳米颗粒材料大规模应用的一个关键难题。抑制动力学捕获和缺陷形成，同时加速有序材料生长的过程对于自下而上的纳米材料制备至关重要。在这种动态、有向自组装过程中，自组装组件之间的相互作用是通过时间来驱动的，为加速和控制纳米结构的自下而上生长提供了一种有前途的方法。在本文中，我们通过模拟和理论表明，时间相关的、周期性切换的粒子间吸引力可以避免动力学障碍，并为通过短程、各向同性势相互作用的纳米粒子分散体产生有序的结晶区。分散体的生长机制和终端结构由切换协议的参数控制。这种控制允许选择产生快速自组装、低缺陷晶体的过程。尽管通过周期性切换吸引力进行自组装本质上是不稳定和非平衡的，但它的结果是由非平衡热力学的第一性原理理论预测的。该理论要求在分散体的共存相中压力和化学势的时间平均值相等。这些量是使用熟知的状态方程来评估的。该理论预测的相行为与布朗动力学模拟沉降平衡和均相成核的测量结果吻合良好。该理论可以很容易地扩展到模拟由其他切换保守力场引导的动态自组装。
