Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B25: Biopolymers and Sustainable Polymers |
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Sponsoring Units: DPOLY Chair: Alexander Klotz, Massachusetts Institute of Technology Room: BCEC 160A |
Monday, March 4, 2019 11:15AM - 11:27AM |
B25.00001: Fabrication of Nano/micro-fiber Materials from Rigid Rod Peptide Chains via Electrospinning and Their Mechanical Properties Kyunghee Kim, Christopher Kloxin, Jeffery G Saven, Darrin Pochan Peptides are ideal candidates for the design and controlled assembly of nanoscale materials due to their potential to assemble with almost atomistic precision as in biological systems. The ability to create rigid rod chains composed of individual peptide bundles and to develop nano/microfibers containing the stiff chains offers the opportunity to develop unique structural features and a remarkable combination of high stiffness, high strength, large elasticity and elongation. This study is to facilitate nano/microfiber electrospinning, focusing on the use of synthetic peptides and to measure initial physical properties of peptide-based fibers. Computationally-designed peptides formed designed coiled coil bundles that serve as supramolecular monomers in chain formation. The bundle chains, or “bundlemers” display rigid-rod character due to intrabundle and interbundle physical and covalent interactions. The resultant rigid chains are employed to fabricate nano/micro-fibers via electrospinning. The mechanical properties of electrospun rod fibers are investigated as a function of bundlemer rod length, intra- or inter-chain interactions (both before and/or after electrospinning), and bundle type included in the bundlemer chains. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B25.00002: Self-Assembly of poly(D-glucose carbonate) Amphiphilic Block copolymers in Solution Jee Young Lee, Karen L. Wooley, Arthi Jayaraman, Darrin Pochan With a rising interest in developing and implementing more environmental-friendly materials, the study of self-assembly behavior of a next generation natural-source based polymers is crucial. Sugar-derived poly(D-glucose carbonate) (PGC) amphiphilic block copolymers with targeted block compositions, chain lengths and side chain chemistries were synthesized. The bulk solution assembly behavior of PGCs was explored using a range of solvent environments (e.g. water-miscible organic solvent compositions or pH-induced structural transitions). The assembled nanostructure shows a morphological transition from a micellar to a fibrillar nanostructure that is dependent on parameters affecting the degree of side chain ionization. These findings allow us to discover a variety of robust nanostructures that can be achieved by non-traditional polymers and their potential to be used in many applications. Additionally, conformations of homopolymer PGC with different side chains were measured via small-angle neutron scattering (SANS) in an effort to better understand the assembly formation behavior of the PGCs when used as blocks in amphiphile creation. Finally, new efforts to correlate scattering, electron microscopy, and simulation data will be presented. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B25.00003: Structure of Hydrophobically Modified Phytoglycogen Nanoparticles Using Small Angle Neutron Scattering John Atkinson, Jonathan Nickels, Michelle Michalski, Adrian Schwan, John Katsaras, John Dutcher
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Monday, March 4, 2019 11:51AM - 12:03PM |
B25.00004: Binding of Proteins to Phytoglycogen Nanoparticles, a Novel, Sustainable, Soft Colloid Kathleen Charlesworth, Aidan Maxwell, John Dutcher Phytoglycogen is a glucose polymer that occurs naturally in the form of highly branched, compact nanoparticles. Because of their tree-like or dendrimeric structure, phytoglycogen nanoparticles have unique properties, such as a strong interaction with water and uniformity in size, which makes them attractive for use in applications ranging from cosmetics to drug delivery. Many of these applications rely on the binding of small molecules onto phytoglycogen nanoparticles. Surface Plasmon Resonance (SPR) is a sensitive experimental technique, based on the resonant absorption of light within an ultrathin gold film, that can be used to measure the binding kinetics and affinities of small molecules. I will discuss our success in creating a stable phytoglycogen-functionalized gold surface, which has allowed us to use SPR to quantify the binding of various proteins to the phytoglycogen nanoparticles. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B25.00005: Influence of poly(N-isopropylacrylamide) grafting density on the temperature dependent fibril formation of methylcellulose McKenzie Coughlin, Svetlana Morozova, Peter Schmidt, S. Piril Ertem, Theresa M. Reineke, Frank Bates, Timothy Lodge Methylcellulose (MC) is a water-soluble cellulose ether that is used in a variety of commercial products due to its thermoreversible gelation at ca. 60 °C, near the lower critical solution temperature (LCST) of MC. It is known that this gelation is caused by the formation of a fibrillar network upon heating. Recently, we demonstrated that the MC fibril structure can be modified and that the fibril formation can be suppressed by grafting short poly(ethylene glycol) (PEG) chains onto the MC backbone. With this new understanding, we have grafted poly(N-isopropylacrylamide) (PNIPAm) chains onto the MC backbone at various grafting densities; PNIPAm displays LCST behavior in water at ca. 32 °C. Utilizing static and dynamic light scattering, we characterize the chain conformation and variation in the overall radius of the chains as a function of grafting density and temperature. Small-amplitude oscillatory shear reveals changes in the gelation behavior and modulus of the two polymers. Fibril formation and fibril structure are studied using small-angle X-ray scattering and cryogenic transmission electron microscopy. The influence of PNIPAm grafts on the temperature dependence of MC fibril formation is compared with the results from PEG-grafted MC. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B25.00006: Block copolymers derived from methylcellulose S. Piril Ertem, Svetlana Morozova, Peter Schmidt, McKenzie Coughlin, Theresa M. Reineke, Frank Bates, Timothy Lodge Methylcellulose (MC), a cellulose ether derivative, attracts interest in both industry and academia for its unique rheological properties in water. At an average degree of methoxy substitution of 1.8, MC shows a concentration-dependent lower critical solution temperature (LCST) near 45 – 60 °C, above which the solution gels by forming fibrils with a diameter of 15 nm. This diameter is independent of molecular weight, MC concentration, and temperature of formation. Our group has recently showed that room temperature MC chain stiffness can be increased, and fibril formation suppressed, by grafting short to medium length poly(ethylene glycol) (PEG) chains along the MC backbone. In this work we present block copolymers of MC with PEG. Using a selective chemistry, the reducing end-groups of MC are successfully modified into allyl groups. Allylated MC chains are then reacted with hemitelechelic thiol-terminated PEG via photoinitiated thiol-ene click chemistry to form AB type block copolymers. The influence of the PEG block on MC fiber formation is studied as a function of temperature using small angle X-ray scattering and small amplitude oscillatory shear. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B25.00007: Structure Formation in Dense Gels of Cellulose and Ionic Liquid Doug Henderson, Xin Zhang, Yimin Mao, Robert M Briber, Howard Wang Cellulose regeneration from solutions is commonly used and essential for applications that require rearrangement of cellulose molecules from their native structures, whereas the transient intermediate state of cellulose condensates during regeneration is poorly understood. In this study, dense gels of cellulose and ionic liquid (IL) with high cellulose content have been prepared by initially vacuum evaporating the solvent DMSO from ternary molecular solutions of cellulose, yielding a dense gel of cellulose/IL with a molar ratio of cellulose sugar units to IL at ca. 1:3. Further successive removal of IL results in a series of nearly equilibrated binary mixtures of cellulose/IL approaching neat cellulose. Small and wide angle x-ray scattering (SAXS and WAXS) indicate multiscale structures in the gels, where the local crystalline order shows a unique lattice structure, and the mesoscale structure has a characteristic correlation length that increases with the IL content. The temperature and composition dependencies of the multiscale gel structures have been investigated. Dynamic mechanical properties have also been studied. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B25.00008: Tensile properties for solid films of deoxyribonucleic acid containing hydrated ionic liquids Hisao Matsuno, Yuma Morimitsu, Noboru Ohta, Hiroshi Sekiguchi, Atsushi Takahara, Keiji Tanaka Mechanical properties of deoxyribonucleic acid (DNA) solid films strongly depend on the water content; from glassy-like to rubbery-like via semi-crystalline-like. Also, the incorporation of intermolecular cross-linking between DNA strands impacts on them. These imply a possibility of DNA solids as an eco-friendly structural material. However, to accelerate such a trend, there exists a challenging problem that water evaporates from the film in a short time, causing a change of the mechanical properties. In this study, aggregation states and tensile properties of the DNA films containing a hydrated ionic liquid, choline dihydrogen phosphate (CDP), were studied. The stress-strain (S-S) curve was strongly dependent on the amount of CDP in the films. A 8-wt% CDP film behaved like a glassy polymer. As the CDP content increased, the shape of S-S curves changed to ductility-like or rubbery-like polymers. In the case of a 23-wt% CDP film, the yield stress decreased more strikingly and the clear strain hardening, like elastomers, was observed. Overall, the breaking point and energy increased, and the Young’s modulus and yield stress decreased with increasing CDP amount. And also, these properties were maintained for more than several days because hydrated CDP could be hardly evaporated. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B25.00009: Correlation of Mechanical and Hydration Properties of Soft Phytoglycogen Nanoparticles Michael Grossutti, John Dutcher Phytoglycogen nanoparticles are highly-branched polymers of glucose that are produced as soft, compact nanoparticles by sweet corn. By combining the results of dialysis, ellipsometry and gravimetric analysis experiments, we have constructed a master plot of the osmotic pressure-concentration data for phytoglycogen nanoparticles with values ranging over seven orders of magnitude. The distinctive shape of the osmotic pressure-concentration curve for phytoglycogen differs significantly from that of dextran, a lightly-branched polysaccharide that is chemically identical but does not occur in the form of particles. Specifically, there is a well-defined plateau in the logarithm of the osmotic pressure at phytoglycogen nanoparticle concentrations corresponding to contact between the particles. By recasting the dependence of the osmotic pressure on concentration in terms of its dependence on the effective separation of the particles, we identify three distinct regimes of interactions between the particles: a weak repulsion before contact; a stronger repulsion upon initial contact and compression (intermediate regime); and an even stronger repulsion for large particle compressions (concentrated regime). This analysis has allowed us to relate the mechanical stiffness to particle hydration. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B25.00010: Topography and Mechanical Properties of Phytoglycogen Nanoparticles Benjamin Baylis, John Dutcher Phytogycogen is a naturally occurring glucose polymer that is produced in the form of highly-branched, compact nanoparticles by sweet corn. Phytoglycogen nanoparticles are a novel type of soft colloidal particle [1], and their deformability, unique hydration and safety makes them desirable for applications in personal care, nutrition and biomedicine. We have used atomic force microscopy (AFM) to measure the topography, deformability and effect of hydration of phytoglycogen nanoparticles. We have successfully immobilized the phytoglycogen nanoparticles on the terraces of annealed gold substrates by using a thiolated boronic acid-based self-assembled monolayer. To overcome the challenges of measuring these soft and deformable particles, we have used the Quantitative Imaging mode of our JPK AFM, which is an optimized mapping of many force-distance curves. This allows us to obtain detailed images of particle stiffness, particle-tip adhesion, and sample height for different applied forces, while minimizing the lateral forces exerted on the delicate particles. I will describe the detailed information – particle height, volume and mechanical properties – that we have measured for the phytoglycogen nanoparticles. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B25.00011: Pressure Effects on Self-assembly in Charged Block Copolymer Systems Junhan Cho Self-assembly in charged A-B block copolymers or their blends with homopolymer C to form nanophases is investigated through field-theoretic calculations. In particular, free volume is allowed in the chosen systems to focus on pressure effects on the self-assembly. The free energy consists of that from charged hard sphere chain reference system and nonbonded dispersion interactions. After the proper discretization of given system, the non-ideal part of the resultant chemical potential is used to determine the local aggregation of charged and uncharged monomers under applied pressure in a mean-field level. In addition to conventional effective Flory-Huggins interaction parameter between dissimilar monomers, ion-ion correlations are shown to affect the self-assembly and its pressure response of the given systems. We will discuss comparison between the present study and inhomogeneity in lipids or other charged amphiphiles under pressure. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B25.00012: Non-Equilibrium Ionic Charging and Discharging During Molecular Translocation Through Nanopores: A Non-Equilibrium Capacitive Spectral Assay for Single Molecules Sebastian Sensale, Zhangli Peng, Hsueh-Chia Chang We show that induced ionic dipoles appear at the ends of nanopores due to corner field leakage (Zhang et Al., J Phys Chem C, 2011; Thamida and Chang, Phys of Fluids, 2002). The opposite space charge of these dipoles across the end corners can charge and discharge molecules translocating through the nanopore. With an asymmetric KCl electrolyte, whose cation and anion have disparate diffusivities due to hydration cage effects, the dynamics of the least mobile ions as well as the length and charge density of the translocating molecules lead to unique non-equilibrium capacitive signals, which can augment the classical DC resistive signal to identify the translocating molecules---particularly those with specific Hoffmeister counter-ions. Under proper conditions, these charging and discharging events are distinguishable during translocation, leading to unusual molecule-dependent capacitive displacement current signals, such as the biphasic wave shapes observed experimentally (Wang et Al., Anal Chem, 2015). |
Monday, March 4, 2019 1:39PM - 1:51PM |
B25.00013: Ionization and electrophoretic migration of the crosslinking byproducts in low-density polyethylene Hossein Hamedi, Roger Craig Walker II., Cesar A Nieves, William Henry Hunter Woodward, Ramakrishnan Rajagopalan, Eugene Furman, Michael T. Lanagan Crosslinked polyethylene (XLPE) -the main material used in high voltage cable- is made by the crosslinking of low-density polyethylene (LDPE). It has been reported that space charge aggregates in XLPE can give rise to the local electric fields leading to early failure of the dielectric. The main source of space charge aggregates is crosslinking byproducts such as acetophenone. Acetophenone ionization in an electric field produces charged species. The electrophoretic migration of the charges alters the local electric field. The scope of this study is to determine the electrophoretic transport in polyethylene. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B25.00014: 1/f Noise in Solid-state Nanopore: Generation Mechanism and Prevention Methods Kazuma Matsui, Yusuke Goto, Rena Akahori, Michiru Fujioka, Takeshi Ishida, Takahide Yokoi, Itaru Yanagi, Ken-ichi Takeda To realize DNA sequencing with solid-state nanopore, reduction of an ionic current noise is an important issue. Especially, low-frequency (1/f) noise causes a serious problem reducing read accuracy of DNA sequencing. Its origin has been heavily debated, but not yet clarified. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B25.00015: Elucidating the microstructural basis for the lasting radial strength of poly (L-lactide) bioresorbable vascular scaffolds during hydrolysis Karthik Ramachandran, Tiziana Di Luccio, Artemis Ailianou, Mary Beth Kossuth, James Paul Oberhauser, Julie A Kornfield Drug-eluting metal stents (DES) are the current standard-of-care for restoring blood flow through an occluded artery. However, DES are made from metal alloys that are non-biodegradable and consequently, inhibit arterial vasomotion and pose a risk of thrombosis, a dreaded complication. Bioresorbabale vascular scaffolds (BVS) made from poly L-lactide (PLLA) are emerging as a promising alternative to permanent metal stents. The clinically-approved BVS (FDA-approval in 2016) supports the occluded artery for the requisite 3-6 months but is completely resorbed in 2-3 years. As a result, the BVS restores arterial vasomotion and can eliminate the late onset of thrombosis. The clinically-approved BVS presents a paradox as it hydrolyzes in the body – it suffers a ~40% decrease in molecular weight (Mn) but shows no decrease in radial strength. Using X-ray microdiffraction, we discovered that the BVS develops a unique microstructure in localized regions that make up <3% of the scaffold. These regions resist hydrolysis and reinforce struts in the BVS that are the most vulnerable to fracture. Thus, the global measure of degradation does not capture the presence of chains with Mn higher than average in regions that have a disproportionate impact on strength. |
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