纳米气泡驱动的布朗粒子超快扩散动力学
Nanobubble-driven superfast diffusion dynamics of Brownian particles
摘要：
非平衡状态下的主动或自推进布朗粒子的动力学最近在许多领域引起了极大的兴趣，包括生物实体和人工微/纳米马达6。了解它们的动力学可以深入了解远离平衡的生物和物理系统的统计特性。通常，活性布朗粒子可以涉及平移或旋转运动。在这里，我们报告的平移动力学的光子激活的金纳米粒子（NPs）在液体细胞成像的四维电子显微镜（4D-EM）。在飞秒（fs）激光脉冲的激发下，我们观察到这些布朗纳米粒子表现出超快的扩散行为，其扩散常数比没有激光激发时大4 ~ 5个数量级。测得的扩散常数被发现遵循幂律依赖于飞秒激光能量密度。这种超快扩散是由NP表面附近的光致纳米气泡（NB）的快速成核、膨胀和塌陷所产生的强随机驱动力引起的。相比之下，NP的运动在低至纳秒（ns）的短时间尺度下表现出超快的弹道平移。结合物理模型模拟，揭示了NB推进自推进运动的机理，为更好地设计光激活人工微/纳米马达提供了物理依据。
英文摘要：
Dynamics of active or self-propulsive Brownian particles in nonequilibrium status, has recently attracted great interest in many fields including biological entities and artificial micro/nanoscopic motors6. Understanding of their dynamics can provide insight into the statistical properties of biological and physical systems far from equilibrium. Generally, active Brownian particles can involve either translational or rotational motion. Here, we report the translational dynamics of photon-activated gold nanoparticles (NPs) in liquid cell imaged by four-dimensional electron microscopy (4D-EM). Under excitation of femtosecond (fs)-laser pulses, we observed that those Brownian NPs exhibit a superfast diffusive behavior with a diffusion constant four to five orders of magnitude greater than that in absence of laser excitation. The measured diffusion constant was found to follow a power-law dependence on the fs-laser fluence. Such superfast diffusion is induced by strong random driving forces arising from rapid nucleation, expansion and collapse of photoinduced nanobubbles (NBs) near the NP surface. In contrast, the motion of the NPs exhibit superfast ballistic translation at a short time scale down to nanoseconds (ns). Combining with physical model simulation, this study reveals a NB-propulsion mechanism for the self-propulsive motion, providing physical insights for better design of light-activated artificial micro/nanomotors.
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