Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C50: Optically and Photonically Active PolymersFocus
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Sponsoring Units: DPOLY GSOFT DMP Chair: Zhe Qiang, Northwestern University Room: BCEC 252B |
Monday, March 4, 2019 2:30PM - 2:42PM |
C50.00001: Micro- and Nanoporous Polymer Coatings: A Diverse and Promising Platform for Optical and Thermal Regulation Jyotirmoy Mandal, Yuan Yang, Nanfang Yu Polymers vary widely in their intrinsic optical properties – for instance, poly(ethene) (PE) is highly transparent across the visible to far-infrared wavelengths, while poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP) is highly emissive in the long-wave infrared (LWIR). When made porous, polymers optically scatter sunlight. As a result, porous P(VdF-HFP) can attain solar reflectance (Rsolar) > 96% and LWIR emittance (εLWIR) ~ 97%, which makes it a near-perfect radiative cooler for buildings. Meanwhile, the high Rsolar (~ 80%) and LWIR transmittance (~ 60%) of porous PE makes it useful in thermoregulation devices with tuneable εLWIR. Furthermore, by reversibly wetting and drying porous polymers with appropriate fluids, scattering efficiencies of the pores can be greatly altered to cause switching between solar reflective and transparent states (by 74%). Switching between LWIR transparent and absorptive/emissive states (by 60%) can also be achieved. Such optically switchable porous polymer coatings can control heat and light in buildings, and be used for camouflaging. Promisingly, porous polymers are already widely manufactured, making the stated applications viable. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C50.00002: Automated Platform for Investigating Aligned Carbon Nanotube Films Josh Walker, Jeffrey Fagan, Henry Wladkowski, Thomas A Searles, Angela Hight Walker, William Rice The one-dimensional nature of single-wall carbon nanotubes (SWCNTs) creates highly directional properties. Utilizing this anisotropy for optoelectronic devices requires researchers to macroscopically align SWCNT ensembles. Recently, surfactant-dispersed SWCNTs were aligned using a manually operated, slow-filtration technique. Building off this method, we present in this work a new platform for reproducibly forming multiple aligned SWCNT films simultaneously. Our parallel filtration setup uses machine vision with pressure feedback control to produce aligned SWCNT films with areas ranging from 2.5 to 9.6 cm2. SWCNT alignment is then determined by polarized optical measurements, such as linear dichroism and Raman spectroscopy. The ability to reproducibly create aligned films enables us to investigate parameters contributing to SWCNT alignment. Specifically, we show that for certain filtration conditions, meniscus pinning produces a spherulite pattern. Additionally, we tune the ionic strength across four orders of magnitude to show the effects of the inter-nanotube electrostatic environment on alignment. These results lead us to a deeper understanding of the physics behind SWCNT directional control. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C50.00003: Cold Plasma Effects on the Optical Properties of Salmon DNA Thin-films Moses Nnaji, Ben Jang, Heungman Park Fabrication of organic electronics is attractive due to the prospective lower cost when compared to inorganic devices. In particular, deoxyribonucleic acid (DNA) biopolymers show excellent promise for use in organic electronics due to their great electron-blocking capability and abundance in animal waste products. While DNA thin-films are often created by associating DNA with hexadecyltrimethylammonium chloride (CTMA) surfactant to promote DNA solubility in organic solvents and spin coat higher quality films, some success in reproducing uniform, water-based DNA thin-films on silicon and glass substrates has been achieved by incorporation of methanol as well as implementation of UV-ozone cleaning. Resulting DNA films were then subjected to cold plasma treatment to study the effects on the films via ellipsometry and spectrophotometry, where the refractive index and absorption coefficient have been characterized. Optical changes and potential novel resonance behavior induced by Ar plasma treatment encourage the continued use of Ar plasma under various conditions, as well as the use of other inert noble gases. |
Monday, March 4, 2019 3:06PM - 3:42PM |
C50.00004: Optically active self-assembled pi-conjugated peptides Invited Speaker: Charles Schroeder A major challenge in bioorganic electronics lies in the development of soft, deformable, and (opto)electronically active materials that can assemble into hierarchical structures. We use molecular design and engineering to develop new materials for organic electronics and photonics. In this talk, I discuss recent work that focuses on optically active, pi-conjugated peptides that can be engineered for precise supramolecular assembly. We consider both the kinetics and thermodynamics of assembly using a combination of experiments and modeling. Pi-conjugated peptides are guided to assemble under reaction- or diffusion-dominated conditions, such that the morphology and properties of assembled peptide fiber networks can be controlled by kinetics. A combined spectroscopy-microrheology technique is used to study the sol-gel transition of these materials during assembly, which enables direct measurement of modulus and photophysical properties during gelation. In situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM) are used to characterize peptides during the assembly process. We further demonstrate a facile strategy to macroscopically align supramolecular fibers using a templating method based on sacrificial colloidal microchannels that does not require photolithography. The structural and chemical properties of oligopeptide fibers are characterized using AFM-infrared spectroscopy (AFM-IR), photoinduced force microscopy (PiFM), fluorescence polarization microscopy, and electron microscopy. In addition, the charge transport properties of pi-conjugated peptides are determined under a wide range of applied voltages. Overall, this work illustrates simple yet robust strategies to pattern 1-D supramolecular fibers over large areas, thereby offering new routes for assembling functional organic materials. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C50.00005: Effect of Polymer Spacer Length in FRET-Based Fluorescent Donor-Acceptor Sensing System Chan Ho Park, Bumjoon Kim In contrast to traditional fluorescent resonance energy transfer (FRET) acceptors, two-dimensional (2D) materials potentially create the long-range energy transfer due to the strong dipole-surface energy transfer. Stimuli-responsive polymers can be an efficient tunable spacer between the FRET donor and 2D acceptor because of their conformational change to the diverse stimuli that allows the dynamic change of distance in a wide range (approximately 1-25 nm). Thus, controlling the length of polymer spacer is the most crucial to maximize the FRET signal in response to the stimuli, because FRET is dominantly distance dependent. In this paper, we present a fluorescent, thermo-responsive block copolymer grafted 2D nanosheets to retain dynamic fluorescence quenching through the change of grafted polymer length. Distance dependent FRET efficiency is studied according to the molecular weight and areal chain density of polymers. The relationship between thermally-responsive FRET and polymer behavior is theoretically calculated and elucidated by measurements of time-resolved fluorescence. Consequently, we first suggest the FRET distance between organic dye and 2D nanosheets and find optimum condition of grafting polymers to maximize the fluorescence response as a function of temperature. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C50.00006: Nanostructured Polymer Films Exhibiting Solvent-Responsive Photonic Band Gaps Yifan Xu, Jacob A LaNasa, Robert Hickey Tunable and reversible photonic band gap materials generated from nanostructured block polymers have shown applications in displays, sensors and waveguides. Here, we present a way to rationally design the change in the photonic band gap of a lamellar-forming poly(1,2-butadiene)-block-poly(ethylene oxide) (1,2PBD-b-PEO) on the addition of solvents that are able to selectively swell one or both domains. A good solvent for both 1,2PBD and PEO domains, like tetrahydrofuran, leads to the largest increase in the domain spacing, and as a result, the largest change in the photonic band gap. For selective solvents like water and hexane, only one domain swells (PEO or 1,2PBD domain, respectively), leading to smaller changes in the photonic band gap. Cryogenic scanning electron microscopy and small-angle X-ray scattering were used to characterize the structural changes that occur on addition of the different solvents, while optical reflection measurements were used to determine the change in the photonic band gap. The work presented here highlights the necessary parameters for tuning the photonic band gap properties for block polymer materials using the combination of solvent quality (e.g., degree of polymer domain swelling) and changes in the refractive index. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C50.00007: Can we design a reconfigurable photonic crystal in the visible light range? Rose Cersonsky, Julia Dshemuchadse, James A Antonaglia, Greg Van Anders, Sharon Glotzer Crystals with a complete photonic band gap are materials composed of mixed dielectric media which result in the reflection of all electromagnetic waves in a given range of wavelengths, commensurate to the length scale of the crystal, and pose an exciting avenue for novel materials. Diamond is a popular target for photonic crystals, which poses an opportunity for reconfigurable matter: can we create a colloidal crystal that switches reversibly to and from the diamond structure? Drawing inspiration from high-pressure phase transitions of diamond-forming atomic systems, we design a system of particles with polyhedral shapes that transitions from diamond to a tetragonal diamond derivative upon a small change in pressure and coincides with a noteworthy modulation of the photonic properties of the crystal. We propose that the transition provides a reversible reconfiguration process for a potential new colloidal material, and we draw parallels between this transition and the materials from which we take inspiration. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C50.00008: Photonic band gaps in self-assembled colloidal crystals Duanduan Wan, Sharon Glotzer <!--StartFragment --> |
Monday, March 4, 2019 4:30PM - 4:42PM |
C50.00009: The Importance of Being Inhomogeneous: Simulation Approaches for Liquid Crystal Optical Metasurfaces in the Visible James Dolan, Haogang Cai, Lily Delalande, Xiao Li, Juan De Pablo, Daniel Lopez, Paul F Nealey Optical metasurfaces—planar nanostructured devices which can arbitrarily tailor the wavefront of light—may be reconfigured by changing their dielectric environment. The application of external fields to liquid crystals is a particularly promising means by which to tune the optical properties of otherwise static metasurfaces. However, despite recent advances, there is still much progress to be made towards this goal. An outstanding issue is the behavior of liquid crystals adjacent to the nanoparticle “meta-atoms”. The optics of the device depend sensitively on this behavior, especially as the wavelength of operation approaches the visible and, therefore, the length scale of distortions in the liquid crystal director field. Here, we will demonstrate—through combined simulations and experiments—that it is not only the anisotropy of the liquid crystal which is important, but also its spatial inhomogeneity, if one wishes to accurately describe, and therefore predict, the optical properties of liquid crystal metasurfaces. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C50.00010: Liquid crystal based photonic topological insulators Hamed Abbaszadeh, Michel Fruchart, Vincenzo Vitelli, Wim Van Saarloos Topological photonics harness the physics of topological insulators to control the behavior of light. An example of such control is to find modes of a photonic system that are robust against material imperfections. In this talk, we propose to use a soft-matter platform based on liquid crystals to implement some classes of photonic topological insulators. In such systems, the spatial orientation of the molecules introduces an extra geometric degree of freedom which in conjunction with suitably designed structural properties leads to the creation of topologically protected states of light. The use of soft building blocks potentially allows for reconfigurable systems that exploit the interplay between light and the soft responsive medium. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C50.00011: Electrically tunable structural colors of cholesterics with oblique helicoidal director Olena Iadlovska, Graham R Maxwell, Mateusz Mrukiewicz, Greta Babakhanova, Sergij V Shiyanovskii, O D Lavrentovich A cholesteric liquid crystal was recently shown (Xiang, J. et al., Phys. Rev. Lett. 112, 217801 (2014); Xiang, J. et al., Adv. Mater. 27, 3014 (2015)) to exhibit a peculiar oblique helicoidal state (ChOH) when acted upon by an electric field. The period of ChOH structure depends strongly on the applied field, which enables electrically tunable structural colors in an extraordinary broad spectral range from ultraviolet to infrared. We present experimental and theoretical studies of light reflection from ChOH as a function of the electric field, surface anchoring, and incident angle. Unlike the case of conventional cholecterics, ChOH shows tunable reflection at periodicities that correspond to both pitch (for oblique incidence) and half-the-pitch. Reflection spectra are used for the first in-situ measurements of bend elastic constant of the chiral material. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C50.00012: Switchable on-demand Pancharatnam-Berry phase modulation in polymer-stabilized cholesteric liquid crystals Benjamin Kowalski, Timothy J White, Matthew S Mills Cholesteric liquid crystals (CLCs) self-assemble into chiral Bragg reflectors. It has recently been shown that by spatially patterning the reflector’s helical phase, a geometric (Pancharatnam-Berry) phase modulation can be imparted on the reflected beam. Here we combine this approach with electrically driven reflection band tuning of polymer-stabilized liquid crystals. As a demonstration of this capacity, we show dynamically switchable, polychromatic generation of nondiffracting beam modes. We present a novel projection lithography system for reconfigurable helical phase landscape patterning, and analyze the fundamental limits on resolvable feature size in this landscape. |
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