Berezhkovskii Alexander M, Dagdug Leonardo, Bezrukov Sergey M
Section of Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20819, USA.
Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, 09340 Mexico City, Mexico.
J Chem Phys. 2025 Jun 28;162(24). doi: 10.1063/5.0274941.
Earlier, we analyzed the effects of monotonically changing entropy potentials imposed by expanding or narrowing tubes on particle diffusion in such tubes [Berezhkovskii et al., J. Chem. Phys. 147, 134104 (2017)]. In the present study, we examine particle dynamics in biconical cavities, wherein particle motion is influenced by either an entropy potential well, as in a cavity composed of first expanding and then narrowing cones, or an entropy potential barrier, as in a cavity made up of first narrowing and then expanding identical cones. Both types of cavities are relevant to multiple technological and biological problems, where examples of such structures can be found at the micro- and nanoscales. We derive analytical expressions for the Laplace transforms of the distributions for the first-passage, direct-transit, and looping times in such structures. We find that not only the average values but also the distributions of the first-passage times in both cavities are indeed identical. However, the direct-transit and looping time distributions are drastically different. In particular, the mean direct-transit time for the expanding-narrowing cavity (entropy potential well) approaches a constant value with the increasing ratio of the cavity's largest radius to the radius of its opening. In contrast, it goes to infinity in the case of the narrowing-expanding cavity (entropy potential barrier).
此前，我们分析了由扩张或收缩管道施加的单调变化的熵势对管道中粒子扩散的影响[Berezhkovskii等人，《化学物理杂志》147, 134104 (2017)]。在本研究中，我们研究了双锥形腔中的粒子动力学，其中粒子运动受熵势阱影响，如由先扩张后收缩的锥体组成的腔，或受熵势垒影响，如由先收缩后扩张的相同锥体组成的腔。这两种类型的腔都与多个技术和生物学问题相关，在微观和纳米尺度上都能找到此类结构的例子。我们推导了此类结构中首次通过时间、直接通过时间和循环时间分布的拉普拉斯变换的解析表达式。我们发现，不仅两个腔中首次通过时间的平均值相同，其分布也确实相同。然而，直接通过时间和循环时间分布却有很大差异。特别是，对于先扩张后收缩的腔（熵势阱），平均直接通过时间随着腔的最大半径与其开口半径之比的增加而趋近于一个恒定值。相比之下，在先收缩后扩张的腔（熵势垒）的情况下，平均直接通过时间会趋于无穷大。
