Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, Karnataka, India.
J Chem Phys. 2021 Dec 28;155(24):244903. doi: 10.1063/5.0071206.
The growing interest in the dynamics of self-driven particle motion has brought increased attention to the effects of non-thermal noise on condensed phase diffusion. Thanks to data recently collected by Ferrer et al. on activated dynamics in the presence of memory [Phys. Rev. Lett. 126, 108001 (2021)], some of these effects can now be characterized quantitatively. In the present paper, the data collected by Ferrer et al. are used to calculate the extent to which non-thermal white noise alters the time taken by single micron-sized silica particles in a viscoelastic medium to cross the barrier separating the two wells of an optically created bistable potential. The calculation-based on a generalized version of Kramers's flux-over-population approach-indicates that the added noise causes the barrier crossing rate (compared to the noise-free case) to first increase as a function of the noise strength and then to plateau to a constant value. The precise degree of rate enhancement may depend on how the data from the experiments conducted by Ferrer et al. are used in the flux-over-population approach. As claimed by Ferrer et al., this approach predicts barrier crossing times for the original silica-fluid system that agree almost perfectly with their experimental counterparts. However, this near-perfect agreement between theory and experiment is only achieved if the theoretical crossing times are obtained from the most probable values of a crossing time distribution constructed from the distributions of various parameters in Kramers's rate expression. If the mean values of these parameters are used in the expression instead, as would be commonly done, the theoretical crossing times are found to be as much as 1.5 times higher than the experimental values. However, these times turn out to be consistent with an alternative model of viscoelastic barrier crossing based on a mean first passage time formalism, which also uses mean parameter values in its rate expression. The rate enhancements predicted for barrier crossing under non-thermal noise are based on these mean parameter values and are open to experimental verification.
人们对自驱动粒子运动动力学的兴趣日益浓厚，这使得人们更加关注非热噪声对凝聚相扩散的影响。由于 Ferrer 等人最近在存在记忆的情况下对激活动力学的数据进行了收集[Phys. Rev. Lett. 126, 108001 (2021)]，现在可以对其中的一些影响进行定量描述。在本文中，Ferrer 等人收集的数据被用于计算非热白噪声在多大程度上改变了单个微米大小的二氧化硅颗粒在粘弹性介质中穿过光学产生的双稳势垒的时间。该计算基于 Kramers 通量-过种群方法的广义版本，表明外加噪声会使势垒穿越率（与无噪声情况相比）首先随噪声强度增加，然后达到一个恒定值。增强的精确程度可能取决于如何在通量-过种群方法中使用 Ferrer 等人进行的实验数据。正如 Ferrer 等人所声称的，该方法预测了原始二氧化硅-流体系统的势垒穿越时间，几乎与实验结果完全吻合。然而，只有当理论穿越时间是从 Kramers 速率表达式中各种参数分布构建的穿越时间分布的最可能值中获得时，理论与实验之间才会达到近乎完美的一致。如果在表达式中使用这些参数的平均值，就像通常那样，那么理论穿越时间会比实验值高出多达 1.5 倍。然而，这些时间与基于平均首次通过时间形式主义的粘弹性势垒穿越的替代模型一致，该模型在其速率表达式中也使用了平均参数值。在非热噪声下预测的势垒穿越速率增强是基于这些平均参数值的，并且可以进行实验验证。
