Dynamics of Binary Colloids in a Periodic Potential

 

Mahammad Mustakim and A. V. Anil Kumar

School of Physical Sciences, National Institute of Science Education and Research, HBNI, Bhubaneswar-752050

 

The molecular dynamics simulation of a binary colloidal system subjected to an external potential barrier reveals that the attractive depletion interaction between the barrier and the larger particles help larger particles to diffuse faster than the smaller particles over the potential barrier at low temperatures. The smaller particles get localized in between the potential barriers indicating a dynamics similar to system undergoing a glass transition. The anomaly in self-diffusion coefficients of both the species reveals that the diffusive dynamics of the larger particles exhibit sub-Arrhenius temperature dependence at low temperature, which is unusual for classical systems; whereas smaller particles obey normal Arrhenius diffusion. The activation energy of larger particles is found to be temperature dependent and hence changes the effective barrier height accordingly; while that of smaller particles is temperature independent. The waiting time distribution of both the species of particles verifies the nature of dynamical properties of the system. This model, classical by construction, challenges the widespread belief that sub-Arrhenius behavior is an effect of quantum tunnel origin. In contrast to the general agreement in the literature, a classical system can also undergo sub-Arrhenius diffusion.

References:
1- A. V. A. Kumar, J. Chem. Phys. 141, 034904 (2014).

2- S. Arrhenius, Z. Phys. Chem. 4, 226 (1889).
3- H. A. Kramers, Physica(Utretch) 7, 284 (1940).
4-V. H. C. Silva, V. Aquilanti, H.C.B. de Oliveira and K.C. Mundim, Chem. Phys. Lett. 590, 201 (2013). 5- C. Tsallis, J. Stat. Phys. 52, 479(1988).
6- C. Dalle-Ferrier, M. Krüger, R. D. L. Hanes, S. Walta, M. C. Jenkins, and S. U. Egelhaaf, Soft Matter 7, 2064 (2011).
7- V. K. de Souza and D. J. Wales, Phys. Rev. Lett. 96, 057802 (2006).