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 L02: Polymers with Special Architectures: From Molecular Design to Physical PropertiesFocus Live
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Sponsoring Units: DPOLY DSOFT Chair: Keiji Tanaka, Kyushu University; Reika Katsumata, University of Massachusetts Amherst |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L02.00001: Rigid cyclic chains in solution: cyclic amylose carbamate derivatives Invited Speaker: Ken Terao Rigid cyclic polymers (cyclic amylose carbamate derivatives) were succsessfully synthesized from relatively flexible cyclic amylose for which degree of polymerization (DP) ranges between 30 and 300. The cyclic chains have lyotropic liquid crystallinity for which the phase diagram of isotropic and nematic phases were explained by a modified scaled particle theory when we assume some specific conformation in the nematic phase. The chain conformation of the cyclic polymers in dilute solution was determined by means of the small-angle X-ray scattering. The local helical structure for the cyclic polymers is appreciably extended and therefore the main chain is more flexible than that for the corresponding linear chain. We prepared chiral separation columns from the cyclic polymers. The conformational difference between linear and cyclic chains is affectable to the chiral separation ability. When we prepared partly substituted amylose derivative, the aqueous solution showed phase separation behavior, so called temperature responsive behavior. These samples still can form inclusion complex ability of iodine and some hydrophobic molecules. Interestingly, the coupling constant for the linear and cyclic chains are appreciably different, indicating the local conformational difference effects the inclusion complex ability of amylosic chains. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L02.00002: Directly Visualizing Conformations of Bottlebrush Polymers in Bulk Films using Super-Resolution Optical Microscopy Jonathan Chan, Avram Kordon, Ruimeng Zhang, Zhe Qiang, Muzhou Wang Bottlebrush polymers consist of a polymeric backbone densely grafted by side chains. Their elongated chain conformations drive many of their properties, so studying the relationship between molecular architecture and conformation is valuable to design materials for applications. So far, studies have investigated conformations for single chains on surfaces and in dilute solutions, but few studies have investigated conformations in bulk environments. Here, we visualize single bottlebrush chains in the bulk by mixing dilute quantities of dye-labeled bottlebrushes with unlabeled linear chains and imaging using super-resolution optical microscopy (SROM). SROM bypasses the diffraction limit by localizing dye molecules attached along a structure to provide high-resolution images. After imaging single chains, their rigidities were quantified using a persistence length determined by fitting the tangent correlation functions of the backbones to the worm-like chain model. Our analysis methods were verified by simulation. Conformations were studied with changes to side chain length (600-3500 g/mol), grafting density (8%, 40%, 100%), and background polymer molecular weight (2-350 kg/mol). We observe more rigid chains compared to bottlebrush studies in dilute solutions. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L02.00003: Bottlebrushes and Combs With Bimodal Distribution of the Side Chains: Scattering Function Heyi Liang, Yuan Tian, Haley Starvaggi, Andrey Dobrynin We use a combination of the Random Phase Approximation (RPA) calculations and coarse-grained molecular dynamics (CGMD) simulations to study scattering from melts of graft polymers with bimodal distribution of the side chains. The chemical structure of this type of graft polymers is described by grafting density of side chains 1/ng, fraction of short side chains f, and degree of polymerization (DP) of the short (nsc,1) and long (nsc,2) side chains into combs and bottlebrushes. The evolution of the peak position in the static structure factor S(q) obtained in these simulations is analyzed by using the expression for S(q) derived in the framework of RPA. In the bottlebrush regime, the peak position in the scattering function is shown to scale as q*∝〈nsc〉−0.39±0.03 with the number average DP of the side chains〈nsc〉, which is in good agreement with the result of the RPA calculations, q*∝〈nsc〉−3/8. However, this is a weaker dependence than one expected for q* to be associated with the inter-backbone distance, q*∝〈nsc〉−0.5. The results of the CGMD simulations and RPA calculations for the peak position scaling with the DP of the side chains are in a very good agreement with scattering data from melts of bottlebrushes with acrylate and norbornene backbones. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L02.00004: Synthesis, Characterization and Behavior of Cationic Dendrimer-PDMS Hybrids Monica Marks, Will Gutekunst, Kyriaki Kalaitzidou
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Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L02.00005: AFM Force Spectroscopy Measurements of Soft, Dendritic Phytoglycogen Nanoparticles Benjamin Baylis, Erin Shelton, John Dutcher Phytoglycogen is a naturally occurring glucose polymer produced by sweet corn in the form of compact nanoparticles with a dendritic or tree-like architecture. Properties such as deformability, unique hydration and non-toxicity make the particles desirable for applications in personal care, nutrition and biomedicine. We have used atomic force microscopy (AFM) force spectroscopy to collect high resolution force-distance maps of a large number of individual phytoglycogen nanoparticles, providing unique insights into the morphology and mechanical stiffness of the nanoparticles. Measurements performed in water revealed the highly branched, dendritic morphology of the particles for small values of the applied force. These measurements also allowed the determination of the distribution of Young’s modulus values within individual nanoparticles. Dried particles measured in air showed a dramatic increase in Young’s modulus, quantifying the effect of hydration on their mechanical stiffness. These measurements provided new insights at the single particle level of this sustainable nanotechnology. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L02.00006: Hairy Particle Morphology of Dendritic Phytoglycogen Nanoparticles Revealed by Hydrophobic Modification John Simmons, Jonathan Nickels, Michael Grossutti, Hurmiz Shamana, Christopher Stanley, John Katsaras, John Dutcher Phytoglycogen is produced by sweet corn as soft, compact nanoparticles with a dendritic or tree-like architecture. Its softness, porosity and mechanical integrity, together with its biodegradability and non-toxicity, make it a unique additive for formulations in personal care and biomedicine. We used small angle neutron scattering (SANS) of dilute dispersions of native phytoglycogen nanoparticles in mixtures of D2O and H2O to reveal the presence of hairy chains on the surface of the particles. However, these results did not uniquely determine the length and packing density of the hairy chains. To determine this, we used SANS to study phytoglycogen nanoparticles hydrophobically modified with octenyl succinic anhydride (OSA). We observed an additional scattering peak due to the collapse of the hydrophobically modified chains to form well-defined “seeds” on the surface of the particles, consistent with a “raspberry” particle geometry. These measurements allowed us to estimate the average hairy chain length to be 20 anhydroglucose units (AGUs).1 |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L02.00007: Hydrogen-bonded assembly of star and linear polymers. Aliaksei Aliakseyeu, Svetlana Sukhishvili We report on the effect of the molecular architecture of poly(ethylene oxide), PEO on its hydrogen-bonding assembly with poly(methacrylic acid (PMAA). Isothermal titration calorimetry (ITC) revealed the entropic nature of binding between 6-arm star polymer (sPEO), or its linear counterpart (lPEO) of matched molecular weight with linear PMAA. While in both cases interpolymer complexes (IPCs) formed between pH 2.5 and 4.0, significant hysteresis of endothermic heats absorbed occurred as a function of mixing order of polymer solutions at pH 2.5, revealing non-equilibrium conformations. At the same time, the mixing hysteresis disappeared at pH 4 when PMAA became more ionized. The enthalpy of IPC formation was dependent on pH and molecular architecture of PEO, with about two-fold higher endothermic values for sPEO/PMAA complexes as compare to lPEO/PMAA complexes, probably due to differences in hydration and structure of these IPCs. The differences in the IPC composition were further confirmed by the dependence of IPC stoichiometry on PEO chain architecture. In particular, the ratio of PMAA-to-PEO repeat units was 1.8 and 1 for PMAA/sPEO and PMAA/lPEO complexes, respectively, suggesting the existence of PMAA loops surrounding star-like PEO molecules. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L02.00008: Star polymer films for superior impact resistance Andrea Giuntoli, Nitin Krishnamurthy Hansoge, Sinan Keten Polymeric films with greater impact and ballistic resistance are highly desired for numerous applications, but molecular configurations that best address this need remain subject to debate. We present a study on the resistance to ballistic impact of thin polymer films using coarse-grained molecular dynamics simulations, investigating melts of star polymers. Increasing the number of arms or their length results in greater specific penetration energy. Greater interpenetration of chains in stars with a higher number of arms allows energy to be dissipated predominantly through rearrangement of the stars internally, rather than chain sliding. During film deformation, stars with a higher number of arms show higher energy absorption rates soon after contact with the projectile, whereas stars with longer arms have a delayed response where dissipation arises primarily from chain sliding, which results in significant back face deformation. Our results suggest that stars may be advantageous for tuning energy dissipation mechanisms of ultra-thin films, setting the stage for a topology-based strategy for the design of impact-resistant polymer films. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L02.00009: Bottlebrushes and Combs With Bimodal Distribution of the Side Chains: Diagram of States Yuan Tian, Haley Starvaggi, Heyi Liang, Andrey Dobrynin Scaling analysis and coarse-grained molecular dynamics (CGMD) simulations are used to elucidate properties of graft polymers with a bimodal distribution of side chains in a melt. In the scaling analysis, a two-step approach is used to classify graft polymers with grafting density of side chains 1/ng, fraction of short side chains f, and degree of polymerization (DP) of the short (nsc,1) and long (nsc,2) side chains into combs and bottlebrushes. First, a diagram of states of the monodisperse graft polymers with short side chains at grafting density 1/ng is constructed. Second, these graft polymers are considered as backbones with an effective Kuhn length b1, to which the longer side chains are attached at grafting density (1-f)/ng. This approach allows the reduction of four-dimensional architectural parameter space (ng, nsc,1, nsc,2, f) into two two-dimensional projections. Using this representation, we extend the concept of the crowding parameter Φ, describing the degree of mutual interpenetration of the side chains belonging to neighboring macromolecules, and apply it to derive b1 as a function of Φ. The predictions of the scaling model for b1 and diagram of states are confirmed by CGMD simulations. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L02.00010: Universal SCFT phase behavior in conformationally asymmetric linear, comb, and bottlebrush block copolymers Daniel Vigil, Dan Sun, Timothy Quah, Joshua Lequieu, Kris T Delaney, Glenn H Fredrickson Using self-consistent field theory, we study the stability window of the A15 and σ phases for comb block copolymers with identical bond lengths and linear polymers with asymmetric segment lengths. It is well known that for linear polymers the ratio of segment lengths defines a ”conformational asymmetry” parameter that is critical to phase behavior. We show that a more generalized conformational asymmetry can be defined for comb and bottlebrush block copolymers by comparing the length of sidechains. This approach collapses the phase behavior of all chain architectures to a single universal phase diagram. We also show that varying the chain statistics between continuous Gaussian, discrete Gaussian, and freely-jointed chains has a small impact on the phase behavior. |
Wednesday, March 17, 2021 10:24AM - 11:00AM Live |
L02.00011: Tuning Adsorption using Entropy to Alter Structure, Diffusion, and Swelling in Thin Polymer Films Invited Speaker: Bulent Akgun Various polymeric architectures are gaining importance in variety of applications ranging from biomedical coatings to electrochromic displays. Creating well-defined star, comb, and/or branched polymer chains through controlled polymerization techniques paving the way to elucidate the role of entropic effects in adsorption, diffusion and swelling in thin films. We have determined the effects of number of arms, arm molecular weight as well as film thickness and molecular weight on the adsorption using well-defined linear and star polystyrene (PS) by ellipsometry and X-ray reflectivity. Interdiffusion in bilayer films and in-situ swelling of single layers in supercritical carbon dioxide (ScCO2) were determined using neutron reflectivity. When the total molecular weight is constant, the normalized equilibrium thickness of the adsorbed polymer layer increases as the number of arms increases or arm molecular weight decreases. In contrast to the linear adsorbed layers, structure of star, comb or centipede adsorbed layers is well-described by a single layer of uniform density. Star polymers have larger apparent diffusion coefficients than their linear counterparts of identical total molecular weight. The increase in the adsorbed layer thickness as a function of polymer architecture results in a decrease in the swelling and diffusion coefficient as the films become thinner. |
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