Memory effects in soft matter

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• Julian Kappler, DAMTP
• Tuesday 06 November 2018, 13:00-14:00
• MR11, CMS.

If you have a question about this talk, please contact Etienne Fodor.

In biological and other non-isolated systems, a physical process of interest is typically described by a reaction coordinate (collective variable) that couples to an environment. In many cases, an effective model for the reaction coordinate is desired. If there is no separation of time scales between the dynamics of reaction coordinate and environment, the effective model for the reaction coordinate is non-Markovian, i.e. contains memory effects. In this talk, we discuss two different non-Markovian systems.

The rate-determining step of a reaction is usually modeled as the crossing of an effective one-dimensional reaction coordinate over a single barrier. In the first part of this talk we study the mean first-passage time for barrier crossing for non-Markovian dynamics, as described by the generalized Langevin equation. For single-exponential memory, we discuss the known asymptotic scalings, identify a new parameter regime where memory effects accelerate barrier crossing, and present a heuristic formula for calculating the mean first-passage time [1].

In the second part of this talk we study 2D sound waves in an elastic interface that is coupled to a viscous bulk fluid [2]. We first show that for small amplitudes, such waves are described by a linear fractional wave equation. The fractional character of the equation constitutes a memory effect and originates from integrating out the bulk fluid degrees of freedom. We then include nonlinear effects due to the dependence of the interface compressibility on the local compression, and find that our nonlinear theory reproduces experimental key features of surface waves in phospholipid monolayers at the air-water interface.

References: [1] J. Kappler, J. O. Daldrop, F. N. Brünig, M. D. Boehle, and R. R. Netz. “Memory-induced acceleration and slowdown of barrier crossing ”, The Journal of Chemical Physics, vol. 148, p. 014903, 2018. DOI : 10.1063/1.4998239 [2] J. Kappler, S. Shrivastava, M. F. Schneider, and R. R. Netz. “Nonlinear fractional waves at elastic interfaces”, Physical Review Fluids, vol. 2, p. 114804, 2017. DOI : 10.1103/PhysRevFluids.2.114804

This talk is part of the DAMTP Statistical Physics and Soft Matter Seminar series.

This talk is included in these lists:

• All CMS events
• DAMTP Statistical Physics and Soft Matter Seminar
• MR11, CMS
• Soft Matter
• bld31

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