Synchronized oscillations of dimers in biphasic charged fd-virus suspensions

Rapid Communication

Synchronized oscillations of dimers in biphasic charged fd-virus suspensions

K. Kang, S. H. Piao, and H. J. Choi

Phys. Rev. E 94, 020602(R) – Published 9 August 2016

Abstract

Micron-sized colloidal spheres that are dispersed in an isotropic-nematic biphasic host suspension of charged rods (fd-virus particles) are shown to spontaneously form dimers, which exhibit a synchronized oscillatory motion. Dimer formation is not observed in the monophase of isotropic and nematic suspensions. The synchronized oscillations of dimers are connected to the inhomogeneous state of the host suspension of charged rods (fd viruses) where nematic domains are in coexistence with isotropic regions. The synchronization of oscillations occurs in bulk states, in the absence of an external field. With a low field strength of an applied electric field, the synchronization is rather reduced, but it recovers again when the field is turned off. In this Rapid Communication, we report this observation as an example of the strange attractor, occurring in the mixture of PS (polystyrene) dimers in an isotropic-nematic coexistence biphasic fd-virus network. Furthermore, we highlight that the synchronization of PS-dimer oscillations is the result of a global bifurcation diagram, driven by a delicate balance between the short-attractive “twisted” interaction of PS dimers and long-ranged electrostatic repulsive interactions of charged fd rods. The interest is then in the local enhancement of “twist-nematic” elasticity in reorientation of the dimer oscillations. An analysis of image-time correlations is provided with the data movies and Fourier transforms of averaged orientations for the synchronized oscillations of dimers in the biphasic $I - N$ coexistence concentration of charged fd-virus suspensions.

Received 16 February 2016
Revised 22 July 2016

DOI:https://doi.org/10.1103/PhysRevE.94.020602

Physics Subject Headings (PhySH)

Nematic order Synchronization

Charged colloids Viruses

Polymers & Soft Matter

Authors & Affiliations

K. Kang¹, S. H. Piao², and H. J. Choi²

¹Forschungszentrum Jülich, Institute of Complex Systems, ICS-3, D-52425 Jülich, Germany
²Department of Polymer Science and Engineering, Inha University, Inchoen 22212, South Korea

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Issue

Vol. 94, Iss. 2 — August 2016

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Images

Figure 1
(a) $In$ situ electric-field dynamic light scattering of polymerized PS spheres in a low ionic strength of Tris-HCl buffer solution (0.032 mM), for various field conditions at a fixed scattering wave vector. The inset is the scanning electron micrograph of the PS sphere. (b) A brief sketch of an order parameter versus concentration phase diagram of the host system of colloidal rods (of fd viruses), where two spinodal and binodal points are indicated with the isotropic-nematic ( $I - N$ ) coexistence concentration. (c) Corresponding free-energy function as a function of the order parameter for rod suspensions: $I - N$ biphasic state (blue line) is under instability between lower (green line) and upper (red line) binodal concentrations.
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Figure 2
Optical morphology and movie data for Brownian motion of polymerized PS spheres in a monophase of (a) an isotropic fd-virus network, and (b) in a nematic fd-virus network. (c) and (d) show the synchronization of PS-dimer oscillations in an $I - N$ coexistent biphasic fd-virus network. (e) A few temporal snapshots of different orientations of dimer oscillations in the bulk state, and (f) the rotations of dimers without oscillations in thin cell thickness. Blue is coded for the lower part of the image, and the time step is 0.25 s. Supplemental Material movies (movies 2a, 2b, 2c, 2d, 2e, and 2f) are provided.
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Figure 3
(a)–(c) A few snapshots and possible schemes of synchronized dimer oscillations: (a) Dimers formed in the absence of an external field, but soon oscillate to a planar state in the $x - y$ direction in the right panel. (b) Fully stretched in the $x - y$ plane, and (c) local orientation changes to the $z$ axis, before it returns to the state (a). (d) A brief sketch of the strange attractor, where the local twist-nematic, $N^{*}$ phase may exist between dimer oscillations, within nematic domains in an isotropic background. (e) An image-time correlation function obtained from the movie data of movie 2e, with two distinguishable configurations of dimer orientations.
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Figure 4
Image-time correlation functions and the movie data, performed in different electric-field conditions: (a) 0 V/mm, (b) 0.204 V/mm and 100 Hz, and (c) turning off the electric field. Supplemental Material movies (movies 4a, 4b, and 4c) are provided.
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Figure 5
Fourier transforms of different electric-field conditions: (a) 0 V/mm, (b) 0.204 V/mm and 100 Hz, and (c),(d) turning off the electric field. (e) A few snapshots of different orientations for turning off the field, with a time step of 0.5 s. The red arrow indicates the average axis of an orientation. Supplemental Material movies (movies 5a, 5b, 5c, and 5d) are provided.
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