title: Discontinuous bundling transition in semiflexible polymer networks induced by Casimir interactions.
abstract: Fluctuation-induced interactions are an important organizing principle in a variety of soft matter systems. We investigate the role of fluctuation-based or thermal Casimir interactions between cross linkers in a semiflexible network. One finds that, by integrating out the polymer degrees of freedom, there is an attractive logarithmic potential between nearest-neighbor cross linkers in a bundle, with a significantly weaker next-nearest-neighbor interaction. Here we show that a one-dimensional gas of these strongly interacting linkers in equilibrium with a source of unbound ones admits a discontinuous phase transition between a sparsely and a densely bound bundle. This discontinuous transition induced by the long-ranged nature of the Casimir interaction allows for a similarly abrupt structural transition in semiflexible filament networks between a low cross linker density isotropic phase and a higher cross link density bundle network. We support these calculations with the results of finite element Brownian dynamics simulations of semiflexible filaments and transient cross linkers.
authors.affiliation: Department of Physics, UCLA, Los Angeles, California 90095-1596, USA.
authors.forename: Devin
authors.initials: D
authors.lastname: Kachan
authors.affiliation: Institute for Computational Mechanics, Technische Universität München, 85748 Garching, Germany.
authors.forename: Kei W
authors.initials: KW
authors.lastname: Müller
authors.affiliation: Institute for Computational Mechanics, Technische Universität München, 85748 Garching, Germany.
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Wall
authors.affiliation: Department of Physics, UCLA, Los Angeles, California 90095-1596, USA.|Department of Chemistry & Biochemistry, UCLA, Los Angeles, California 90095-1596, USA.|The California Nanosystems Institute, UCLA, Los Angeles, California 90095-1596, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Levine