Department of Chemistry, and.
Department of Chemistry, andDepartment of Biomedical Engineering and Chemistry of Life Processes Institute, Northwestern University, Evanston, IL 60208
Proc Natl Acad Sci U S A. 2014 Jul 8;111(27):9751-6. doi: 10.1073/pnas.1406122111. Epub 2014 Jun 23.
Dissipative self-assembly is the emergence of order within a system due to the continuous input of energy. This form of nonequilibrium self-organization allows the creation of structures that are inaccessible in equilibrium self-assembly. However, design strategies for dissipative self-assembly are limited by a lack of fundamental understanding of the process. This work proposes a novel route for dissipative self-assembly via the oscillation of interparticle potentials. It is demonstrated that in the limit of fast potential oscillations the structure of the system is exactly described by an effective potential that is the time average of the oscillatory potential. This effective potential depends on the shape of the oscillations and can lead to effective interactions that are physically inaccessible in equilibrium. As a proof of concept, Brownian dynamics simulations were performed on a binary mixture of particles coated by weak acids and weak bases under externally controlled oscillations of pH. Dissipative steady-state structures were formed when the period of the pH oscillations was smaller than the diffusional timescale of the particles, whereas disordered oscillating structures were observed for longer oscillation periods. Some of the dissipative structures (dimers, fibers, and honeycombs) cannot be obtained in equilibrium (fixed pH) simulations for the same system of particles. The transition from dissipative self-assembled structures for fast oscillations to disordered oscillating structures for slow oscillations is characterized by a maximum in the energy dissipated per oscillation cycle. The generality of the concept is demonstrated in a second system with oscillating particle sizes.
耗散自组装是指系统由于持续输入能量而产生的有序状态。这种非平衡自组织形式允许创建在平衡自组装中无法获得的结构。然而，耗散自组装的设计策略受到对该过程缺乏基本理解的限制。本工作通过粒子间势的振荡提出了一种耗散自组装的新途径。结果表明，在快速势振荡的极限下，系统的结构可以通过有效势来精确描述，该有效势是振荡势的时间平均值。该有效势取决于振荡的形状，并且可以导致在平衡状态下无法获得的有效相互作用。作为概念验证，在外部控制 pH 振荡的情况下，对由弱酸和弱碱涂覆的粒子的二元混合物进行了布朗动力学模拟。当 pH 振荡的周期小于粒子的扩散时间尺度时，形成耗散稳态结构，而对于较长的振荡周期则观察到无序振荡结构。对于相同的粒子系统，在平衡（固定 pH）模拟中无法获得一些耗散结构（二聚体、纤维和蜂巢）。对于快速振荡，从耗散自组装结构到缓慢振荡的无序振荡结构的转变由每个振荡周期耗散的能量的最大值来表征。该概念在具有振荡粒径的第二个系统中得到了证明。
