Ballistic Hot Brownian Motion

弹道热布朗运动

• 批准号: 336492136
• 负责人: Professor Dr. Frank Cichos
• 金额: --
• 依托单位: Institut für Theoretische Physik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/336492136?language=en
• 关键词: Ballistic; Hot; Brownian; Motion

Brownian motion is the erratic behavior of small particles suspended in a fluid caused by the numerous collisions with the surrounding molecules. Due to this cumulative effect of many individual uncorrelated events it is viewed as a prototype of a stochastic process in nature which meanwhile finds also application in financial market studies. The motion of a Brownian particle is fueled by thermal energy which is continuously exchanged between fluid and particle. Thus, the particles motion is also reflecting the temperature which is summarized by the Stokes Einstein relation connecting the diffusion coefficient with thermal energy and viscous friction. This relation holds for thermal equilibrium, where the temperature is constant in space. All degrees of freedom reflect the same temperature due to equipartition and even at very short timescales, when the motion of a particle is ballistic, the same temperature is found in the instantaneous velocity distribution. The situation is changed when the Brownian particle itself is a heat source or heat sink as it is the case for many chemically reacting species, plasmonic particles and active systems like microswimmers. The environment of the particle is no longer isothermal and it has been shown that the so called Hot Brownian Motion is governed by effective temperatures which are coupled to the hydrodynamics. Therefore, rotational and translational diffusion obey different effective temperatures and equipartition is no longer valid. This project aims at providing first experimental evidence for a frequency dependent effective temperature which allows for a generalized description of the motion of hot Brownian particles. In particular, we will study the transition to the ballistic regime of a heated Brownian particle. When entering this regime, the particle is influenced by the hydrodynamic flow it has generated itself. At even shorter timescales of ballistic motion the particle dynamics will be governed by the kinetic temperature in the instantaneous velocity distribution of Hot Brownian Motion. The relation of the effective temperature to the hydrodynamics suggests a frequency dependence of the effective temperature. Experimentally the particle dynamics shall be accessed by studying the fluctuations of a gold nanoparticle decorated polymer microparticle in an optical trap with nanosecond time and 15 picometer spatial resolution. The gold nanoparticles will be heated optically through their interaction with light. The results will provide for the first time a test of the theory of Hot Brownian Motion and give an experimental insight into a generalized description of non-isothermal Brownian motion by effective temperatures.

布朗运动是悬浮在流体中的小颗粒与周围分子多次碰撞所引起的不稳定行为。由于许多个体不相关事件的累积效应，它被视为自然界中随机过程的原型，同时也适用于金融市场研究。布朗粒子的运动是由流体和粒子之间不断交换的热能推动的。因此，粒子运动也反映了温度，这由将扩散系数与热能和粘性摩擦联系起来的Stokes Einstein关系总结。这个关系适用于热平衡，其中温度在空间中是恒定的。由于均分，所有自由度都反映相同的温度，即使在很短的时间尺度上，当粒子的运动是弹道运动时，在瞬时速度分布中也会发现相同的温度。当布朗粒子本身是热源或散热器时，情况发生了变化，因为许多化学反应物质，等离子体粒子和活性系统如微泳者都是这种情况。粒子的环境不再是等温的，并且已经表明，所谓的热布朗运动由耦合到流体动力学的有效温度控制。因此，旋转和平移扩散服从不同的有效温度，均分不再有效。该项目的目的是提供第一个实验证据的频率依赖的有效温度，允许热布朗粒子的运动的广义描述。特别是，我们将研究一个加热的布朗粒子的弹道制度的过渡。当进入该状态时，颗粒受到其自身产生的流体动力学流动的影响。在更短的弹道运动的时间尺度上，粒子动力学将由热布朗运动的瞬时速度分布中的动力学温度决定。有效温度与流体动力学的关系表明有效温度的频率依赖性。在实验上，通过研究具有纳秒时间和15皮米空间分辨率的光阱中的金纳米颗粒修饰的聚合物微粒的波动来访问粒子动力学。金纳米粒子将通过与光的相互作用而被光学加热。这些结果将首次提供热布朗运动理论的测试，并通过有效温度给出对非等温布朗运动的广义描述的实验见解。