Ye Zhang wins Materials Research Society Poster Award

Ye Zhang, a Postdoctoral Fellow from Prof. Bing Xu’s research group at Brandeis, won the 2012 MRS Fall Meeting Poster Awards for her poster titled Self-oscillatory Hydrogels Driven by Belousov-Zhabotinsky Reaction within the symposium on Bioinspired Directional Surfaces-From Nature to Engineered Textured Surfaces & Precision Polymer Materials-Fabricating Functional Assemblies, Surfaces, Interfaces, and Devices. The goal of the project is to make materials that operate like synthetic cardiac or intestinal muscles; feed them and they will pump forever, or as long as the arteries remain open. Ye, the poster’s lead author, is a member of the Brandeis Materials Research Science and Engineering Center (MRSEC) working on project involving the groups of Profs. Bing Xu, Irving Epstein and Seth Fraden of the Chemistry and Physics Departments.

Ye’s work focuses on the development and study of active matter based on non-linear chemical dynamics, specifically the Belousov-Zhabotinsky reaction. Beginning two years ago she systematically modified a class of gels that exhibit periodic volume oscillations which were produced by other groups. First, Ye succeeded in significantly improving the amplitude of volume oscillations. Next, she developed several novel self-oscillatory systems and established a systematic way to improve the bulk material properties of the synthetic heart.  To build a reliable beating heart, Ye optimized the molecules building the material at the molecular level of tens to hundreds of atoms, or scales of 1 nm and then figured out how to assemble them into networks of polymers on the scales of 10 – 100 nm, and then further assembled them on a longer length scale, into elastic networks on the scales of microns, and finally sculpted the resulting rubbery materials using photolithographic and microfluidic methods into useful shapes for study and application. Ye’s award is a recognition of her contribution to molecular engineering and serves as a quintessential example of the  “bottom-up” construction methods exemplified by the interdisciplinary teams of the Brandeis MRSEC.

Video Poster: One Dimensional Rings of Coupled Oscillators

Brandeis Physics grad students (IGERT trainees) Michael Giver and Nathan Tompkins have a “video poster” in the NSF IGERT Video & Poster Competition on “One Dimensional Rings of Coupled Oscillators – Turing’s Theory Realized”. You can check out and comment on their poster on-line at

award ribbonUpdate: Michael and Nathan’s poster received a Judge’s Choice award ($2,000.00) in the competition!

A lattice of interacting chemical oscillators

At Brandeis, there is a long tradition of interesting experiments on the Belousov-Zhabostinsky reaction system, with the legendary Zhabotinsky himself having been a part of the fraternity. This reaction system shows interesting oscillatory and stable patterns (see videos on Youtube). In the Fraden lab, an oil emulsion of micron-sized water droplets containing the BZ reactions, was shown to show interesting synchronization properties and complex spatial patterns [Toiya et al, J. Phys. Chem. Lett. 1, 1241 (2010)]. A coupling between the droplets due to preferential diffusion of an inhibitory reactant (bromine) in the oil medium was seen to be responsible for these collective phenomena.

In a new paper titled “Phase and frequency entrainment in locally coupled phase oscillators with repulsive interactions” in Phys. Rev. E, Physics Ph. D student Michael Giver, postdoc Zahera Jabeen and Prof. Bulbul Chakraborty show that neighboring oscillators can be modeled as Kuramoto phase oscillators, coupled nonlinearly to its nearest neighbors. The form of the coupling chosen is repulsive, which favors out of phase synchronization. They show using linear stability analysis as well as numerical study that the stable phase patterns depend on the geometry of the lattice. A linear chain of these repulsively coupled oscillators shows anti-phase synchronization, in which neighboring oscillators show a phase difference of π The phase difference between the neighboring oscillators when placed on a ring however depends on the number of oscillators. In such a case, the locally preferred phase difference of π is ruled out for an odd number of oscillators, as this may lead to frustration. When these oscillators are placed on a triangular lattice in two dimensions, the geometry of the lattice constrains the phase difference between two neighboring oscillators to 2 π /3. Interestingly, domains with different helicities form in the lattice. In each domain, the phases of any three neighboring oscillators can vary continuously in either clockwise or an anti-clockwise direction. Hence, phase difference between the nearest neighbors are seen to be ±2π /3 in the two domains (See figure). A phase difference of π is seen at the interfaces of these domains. These domains can grow in time, resembling domain coarsening in other statistical studies. At large coupling strengths, the domains freeze in size due to frequency synchronization of all the oscillators. Hence, an interplay between frequency synchronization and phase synchronization was seen in this system. Ongoing studies in the BZ experimental setup at the Fraden Lab, find correlations with the above results. Hence, insights into a complex system like the BZ oscillators could be gained using the phase oscillator formalism.

The research was supported by the ACS Petroleum Research Fund and the Brandeis MRSEC. Michael Giver is a trainee in the Brandeis NSF-sponsored IGERT program Time, Space & Structure: Physics and Chemistry of BIological Systems

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