Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B09: Non-Equilibrium Bioinspired Modes of Assembling MaterialsInvited Session Live
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Sponsoring Units: DSOFT Chair: Roy Beck, Tel Aviv University; Cecilia Leal, University of Illinois Urbana-Champaign |
Monday, March 15, 2021 11:30AM - 12:06PM Live |
B09.00001: Liquid crystal patterns to command living matter Invited Speaker: O Lavrentovich Microscale biological systems such as swarms of swimming bacteria and cell tissues demonstrate fascinating out-of-equilibrium dynamics. This dynamics is difficult to control by factors other than transient gradients, such as gradients of nutrients; visual, acoustic and tactile communication channels that humans use to control large animals are not effective. To establish communication with microscale biological systems, we propose to use special classes of nontoxic liquid crystal with a long-range orientational order. The anisotropy axis of the liquid crystal can be designed as uniform or be pre-patterned into various structures. We describe how the patterned liquid crystals can be used to command, and sometimes even enable, dynamics in systems of (i) swimming bacteria; (ii) living tissues of human dermal fibroblast (HDF) cells. Topological defects impact the biological microstructures most strongly, causing spatial variation of bacterial concentration and cell phenotype. The control of active matter by patterned liquid crystals might result in new approaches to harness the energy of collective motion for micro-robotic, biomechanical, and sensing devices. |
Monday, March 15, 2021 12:06PM - 12:42PM Live |
B09.00002: Pattern Formation from Instabilities in Liquid Crystals Invited Speaker: Irmgard Bischofberger
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Monday, March 15, 2021 12:42PM - 1:18PM Live |
B09.00003: Reaction-Diffusion Driven Pattern Formation in Soft Materials Invited Speaker: Nancy Sottos Reaction-diffusion processes are versatile, yet underexplored methods for manufacturing that provide unique opportunities to control the spatial properties of materials, achieving order through broken symmetry. The mathematical formalism and derivation of equations coupling reaction and diffusion were presented in the seminal paper by Alan Turing [Phil. Trans. R. Soc. Lond. B 237, 37,1952], which describes how random fluctuations can drive the emergence of pattern and structure from initial uniformity. Inspired by reaction-diffusion systems in nature, this talk will describe a new processing strategy predicated on the exploitation of an advancing polymerization front sustained through coupled reaction and thermal diffusion. The system uses the exothermic release of energy to provide a positive feedback to the reaction. In turn, this stimulates further exothermic energy release and a self-propagating reaction front that rapidly moves through the material – a process called frontal polymerization. We recently reported the frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) that exhibits the high energy density, high reactivity, relatively long pot life, and low viscosity required for the synthesis of high-performance thermosetting polymers and composites [Robertson et al., Nature, 557 (2018)]. This talk will describe several novel methods to control thermal transport in this system, giving rise to symmetry breaking events that enable complex, emergent pattern formation and control over growth, topology, and shape. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B09.00004: Cellulose nanocrystal holograms Invited Speaker: Silvia Vignolini Cellulose nanocrystals (CNCs) are anisotropic and chiral colloidal nanorods able to self- assemble spontaneously into a cholesteric phase above a critical concentration. When the suspension is allowed to dry, it forms a solid film that retain the cholesteric order, enabling the reflection of specific wavelengths, typically in the visible range. [1] Due to their negative diamagnetic anisotropy, CNCs also tend to align perpendicular to an external magnetic field. [2] Experimentally, the cholesteric phase can be aligned under moderate magnetic fields (μ0 H ≈0.5 T), enabling an angular control of the helical direction of the domains. [3,4] In this talk, we present a simple and robust method to spatially control the angular response of CNC films by casting them in close vicinity to commercially available templated magnets (Polymagnets ® ). We show how the spatially modulated magnetic field applied upon casting imprinted the orientation of the cholesteric structure in the bulk of the film thickness and produced its corresponding holographic pattern with a resulting illusion of depth. Angular-resolved optical spectroscopy and K-space optical microscopy analysis both converged toward a quantified illusion of depth in qualitative agreement with the profile expected from the magnetic field mapping and cross-section observations in SEM. |
Monday, March 15, 2021 1:54PM - 2:30PM Live |
B09.00005: Programming dynamic pathways to colloidal self-assembly using DNA nanotechnology Invited Speaker: William Rogers DNA is not just the stuff of our genetic code; it is also a means to build new materials. For instance, grafting DNA onto small particles can, in principle, 'program' the particles with information that tells them exactly how to put themselves together-- they 'self-assemble.' Recent advances in our understanding of how this information is compiled into specific interparticle forces have enabled the assembly of an incredible diversity of crystalline phases. However, programmable assembly of other structures, including aperiodic solids, liquids, or mesophases, remains elusive. Furthermore, the dynamic pathways by which DNA-based materials self-assemble are largely unknown. In this talk, I will present experiments showing that combining DNA-grafted particles with free DNA oligomers dispersed in solution can create suspensions with new types of assembly pathways. I will also demonstrate how we can follow and quantify the entire dynamic pathways to self-assembly, such as nucleation and growth, using new experimental approaches, combining microfluidics, video microscopy, and image analysis. Whenever possible, I will describe attempts to understand and model our observations using simple physical arguments. In the future, this work could prove especially useful in nanomaterials research, where a central goal is to manufacture functional materials by growing them directly from solution. |
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