Properties of the glass transition as a mixture of jamming and random organization

• Applicant: Professor Dr. Michael Schmiedeberg
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262587878

The dramatic slowdown of the dynamics in particulate systems for increasing density or decreasing temperature has been explored for a long time. However, many properties of such glassy dynamics and especially of the glass transition are still not understood. In the proposed project, we want to employ a model system in order to investigate the glass transition, its microscopic origin, as well as its relation to the athermal jamming transition. Athermal jamming usually is obtained by using a protocol that minimizes the overlaps within a soft sphere system without crossing energy barriers while in case of with glassy dynamics at finite temperatures it is possible to cross energy barriers. Recent studied indicate that the glass transition in the limit of small temperatures significantly differs from the athermal jamming transition. Within the proposed project, we will study a model system where particles are first randomly distributed and then in each step overlapping particles are displaced either deterministically or randomly. In case of displacements in random directions the so-called random organization transition is observed, while for purely deterministic displacements the protocol corresponds to the protocol used to obtain athermal jamming. We study the model system for a mixed protocol consisting both of deterministic and random displacements where the latter correspond to the crossing of energy barriers in a soft sphere system. The transition observed with such a mixed protocol corresponds to the glass transition of a soft sphere system. In preliminary simulations we have indeed found that in case of a small but non-zero probability for random displacements the transition differs significantly from the purely deterministic jamming transition. Therefore, this model system is suitable to study the difference between the glass transition at small but non-zero temperatures and the athermal jamming transition. In the proposed project, we want to develop a quantitative mapping of results obtained from the model system onto the glassy dynamics of a soft sphere system. Furthermore, we will determine the critical behavior of the glass transition and explore the microscopic reasons for the glass transition, which might be related to a contact percolation transition. In summary, by studying a model packing system, we expect to gain better knowledge and a deeper understanding of the properties of the glass transition as well as of its origin on a particle-resolved basis.

• DFG Programme: Research Grants