Kim Paul Y, Fink Zachary, Zhang Qingteng, Dufresne Eric M, Narayanan Suresh, Russell Thomas P
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States.
ACS Nano. 2022 Jun 28;16(6):8967-8973. doi: 10.1021/acsnano.2c00020. Epub 2022 Jun 6.
The relaxation and aging of an assembly of spherical nanoparticles (NPs) at a water-oil interface are characterized in situ by grazing incidence X-ray photon correlation spectroscopy. The dynamics of the interfacial assembly is measured while the interface saturates with NPs. Weak attractions between NPs lead to gel-like structures in the assembly, where the in-plane ordering is inhibited by the broad size distribution of the NPs. Structural rearrangements on the length scale of the NP-NP center-to-center distances proceed by intermittent fluctuations instead of continuous cooperative motions. The coexistence of rapid and slow NP populations is confirmed, as commonly observed in soft glass-forming materials. Dynamics are increasingly slowed as the NPs initially segregate to the locally clustered interface. The structural relaxation of the NPs in these localized clusters is 5 orders of magnitude slower than that of free particles in the bulk. When the interface is nearly saturated, the time for relaxation increases suddenly due to the onset of local jamming, and the dynamics slow exponentially afterward until the system reaches collective jamming by cooperative rearrangements. This investigation provides insights into structural relaxations near the glass transition and the evolution of the structure and dynamics of the assemblies as they transition from an isotropic liquid to a dense disordered film.
通过掠入射X射线光子相关光谱对水-油界面处球形纳米颗粒（NP）聚集体的弛豫和老化进行原位表征。在界面被NP饱和的过程中测量界面聚集体的动力学。NP之间的弱吸引力导致聚集体中形成凝胶状结构，其中NP的宽尺寸分布抑制了面内有序性。NP- NP中心到中心距离长度尺度上的结构重排是通过间歇性波动而不是连续的协同运动进行的。正如在软玻璃形成材料中常见的那样，快速和慢速NP群体共存得到了证实。随着NP最初聚集到局部聚集的界面，动力学越来越慢。这些局部簇中NP的结构弛豫比本体中自由粒子的结构弛豫慢5个数量级。当界面接近饱和时，由于局部堵塞的开始，弛豫时间突然增加，随后动力学呈指数减慢，直到系统通过协同重排达到集体堵塞。这项研究为玻璃化转变附近的结构弛豫以及聚集体从各向同性液体转变为致密无序膜时的结构和动力学演变提供了见解。
