9 research outputs found
Relaxation dynamics of a linear molecule in a random static medium: A scaling analysis
We present extensive molecular dynamics simulations of the motion of a single
linear rigid molecule in a two-dimensional random array of fixed obstacles. The
diffusion constant for the center of mass translation, , and for
rotation, , are calculated for a wide range of the molecular length,
, and the density of obstacles, . The obtained results follow a master
curve with an exponent and
1/4 for and respectively, that can be deduced from
simple scaling and kinematic arguments. The non-trivial positive exponent
shows an abrupt crossover at . For we find
a second crossover at . The values of and
correspond to the average minor and major axis of the elliptic
holes that characterize the random configuration of the obstacles. A violation
of the Stokes-Einstein-Debye relation is observed for ,
in analogy with the phenomenon of enhanced translational diffusion observed in
supercooled liquids close to the glass transition temperature.Comment: 8 pages, 8 figures. Minor changes. To be published in Journal of
Chemical Physic