Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P30: Polymer Networks, Gels, and Elastomers III: ArchitectureFocus
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Sponsoring Units: DPOLY Chair: Ross Behling, 3M Corp. Room: BCEC 162B |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P30.00001: Relationship between optical properties and network topology in gels crosslinked using controlled radical polymerization Mahati Chintapalli, Stephen Meckler, Gabriel Iftime, Jessy B. Rivest Controlled radical polymerization can be used to prepare crosslinked polymer gels and aerogels with a variety of unique features: tunable optical transparency, high specific surface area, controlled pore size, and narrow pore size distribution. Such materials enable a range of applications in size- and interaction-selective separations, catalysis and photocatalysis, and thermally insulating materials. We demonstrate that controlled radical polymerization can be used to control network topology, which directly impacts the optical properties and pore structure of crosslinked polymer gels. Two novel methods to control the degree of “livingness” in the gelation reaction are reported. The degree of livingness in the gelation was used to tune the visible light transmittance of a 3 mm gel from 0 % to >70 %. Porous aerogels can be produced from the solvated gels by solvent evaporation at ambient pressure and temperature. Controlled radical gelation led to aerogels with porosities over 60 % and Brunauer Emmett Teller surface areas over 1000 m2/g. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P30.00002: Mechanical and Thermal Performance of Interpenetrating versus Single Networks of Dynamically Crosslinked Polymers Mehdi Zanjani, Ballal Ahammed, Borui Zhang, Dominik Konkolewicz, Zhijiang Ye Dynamically crosslinked polymer composites have received great attention in the past decade due to their unique properties such as self-healing, malleability, and shape memory. Dynamic crosslinkers of two main types, i.e. non-covalently bound crosslinkers and dynamic covalently bound crosslinkers, provide a versatile platform to engineer various types of crosslinked networks with desired properties. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P30.00003: Influence of weak ionic associations on the mechanical properties of hydrogels crosslinked by hydrophobic associations Bryan Vogt, Chao Wang, Robert A Weiss, Katherine Deitrick Since the initial reports of double network hydrogels, a variety of routes to provide energy dissipation in hydrogels have been reported such as the inclusion of physical crosslinks to provide reversible crosslinks. These hydrogels based on physical crosslinks tend to creep due to the reversibility. Inclusion of a second stronger network generally has been used to reduce creep and improve the elastic recovery. Here we take the opposite approach and include weak ionic associations (zinc diacrylate) to manipulate the mechanical behavior of hydrogels formed by hydration of copolymers of hydroxyethyl acrylate (HEA) and 2-(N-ethylperfluorooctane-sulfonamido)ethyl methacrylate (FOSM). The terpolymer-based hydrogel contained >85% of the water of a HEA-FOSM copolymer hydrogel with the same FOSM content, but the storage modulus was nearly an order of magnitude larger for the terpolymer hydrogel. To obtain the same storage modulus, the FOSM content would need to be more than doubled, but this HEA-FOSM copolymer-based hydrogel has almost 40 % less water than the terpolymer hydrogel. These results illustrate the ability to tune the mechanical response of hydrogels through weak ionic associations. |
Wednesday, March 6, 2019 3:06PM - 3:42PM |
P30.00004: Externally Triggered Healing in Covalent Adaptable Networks Invited Speaker: Christopher Kloxin Covalently crosslinked polymer networks have a permanent network topology that makes them well suited for many structural applications but also renders them intractable to post-fabrication manipulation—they cannot be remended, remolded or recycled. The incorporation of reversible covalent crosslinks into the polymer network backbone impart new properties and constitute a new classification of crosslinked materials. Under normal conditions these covalent adaptable networks possess the immutable properties of a chemical gel; however, once triggered by an external stimulus, such as light, heat, or force, the covalent bonds become active, temporarily imparting the network with the transient properties associated with a weak physical gel. The reversible breaking and reforming of network strands ultimately enables a damaged materials to be repaired or ‘healed’ post network fabrication. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P30.00005: Linking failure behavior of physically assembled styrene-isoprene-styrene gels to their network structure Satish Mishra, Rosa Maria Badani Prado, Thomas E. Lacy, Jr, Santanu Kundu Failure behavior of physically assembled gels is governed by their network architecture. We investigate the failure behavior of physically assembled gels composed of poly(styrene)-poly(isoprene)-poly(styrene) in mineral oil, a midblock selective solvent. The gel network consists of collapsed PS endblock aggregates acting as crosslinks, while PI midblocks bridge those aggregates. The gel architecture, as captured by the small angle x-ray scattering, is tuned by varying the polymer volume fraction and midblock length. Tensile experiments reveal a rate dependent mechanical properties, particularly for the samples with entangled midblocks. Energy release rate (G) for fracture scales linearly with the crack-tip velocity (v) indicating a velocity toughening effect in these gels. The G-v relationship strongly depends on the polymer concentration and chain length. These gels fail as a result of endblocks pullout from aggregate. The pullout process involves an entropic penalty associated with the midblock stretching, friction with other endblocks in aggregates, and an enthalpic penalty associated with pulling the endblocks in the non-favorable solvent. We attempt to incorporate all these factors in estimating G and compare that with the experimental values. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P30.00006: Modelling of chemo-mechanical coupling in polymer gels via nonlinear finite element method Priyanka Nemani, Ravi Sastri Ayyagari, Pratyush Dayal Design of multifunctional biomimetic materials that exhibit large amplitude actuation through chemical triggers has been a challenge in the field of smart materials. Polymer gels that utilize self-oscillating Belousov Zhabotinsky (BZ) reactions are pioneers among smart materials due to their biomimetic characteristic of chemo-mechanical transductions. Here, we present a computational framework to simulate the dynamics of self-oscillating polymer gels that undergo large deformations under isothermal conditions. Unlike earlier approaches, we harness a complete nonlinear finite element framework that combines the reaction-diffusion phenomena occurring in BZ reaction, with elastic deformations of the polymer gel. Specifically, we use three variable Oregonator model to incorporate reaction kinetics, non-Gaussian mechanical theory for elastic deformations and Flory-Huggins theory to couple the chemical kinetics with the deformation. We demonstrate that actuation capacity of self-oscillating polymer gels can be amplified and controlled by manipulating the reaction kinetics under specific conditions. We believe that our approach brings in a new perspective to design complex bio-inspired systems and provides the necessary framework to control their behaviour. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P30.00007: Expanding Gelation Conditions in Dynamically Crosslinked Networks Seth Cazzell, Niels Holten-Andersen Polymer networks with dynamic physical crosslinks have generate widespread interest as tunable and responsive viscoelastic materials. A subclass of these materials containing multi-component, or complimentary, crosslinks, such as host-guest interactions and metal-coordination, are limited by their ability to percolate under stoichiometric imbalances of their crosslink components. Here we present a method to relax this stoichiometric requirement through the use of a third component, a dynamic, free competitor. This approach to expand the conditions that result in gelation is demonstrated experimentally with metal-coordinated hydrogels, and simulations are used to show the thermodynamic criteria that are necessary to expand the previously understood tight stoichiometric tolerance for gelation. This work can then be generally applied to advance engineering of the broadening class of polymer materials with dynamic crosslinks. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P30.00008: Melt Blown Cross-linked Fibers from Thermally Reversible Diels-Alder Polymer Networks Kailong Jin, Sung-Soo Kim, Jun Xu, Frank Bates, Christopher Ellison Melt blowing is a process in which liquid polymer is extruded through orifices and then drawn by hot air jets to produce nonwoven fibers. Melt blown nonwovens constitute more than 10% of the $50 billion global nonwovens market. Thermoplastic feedstock, such as polyethylene, polypropylene, and poly(butylene terephthalate), have dominated melt blown nonwovens because of their combined cost, good chemical resistance and high-temperature performance. Cross-linked nonwovens from other commodity polymers (e.g., (meth)acrylates, styrenics, silicones, etc.) could be attractive alternatives; however, no commercial cross-linked nonwovens currently exist. Here, cross-linked fibers were produced via one-step melt blowing of thermoreversible Diels-Alder polymer networks comprised of furan- and maleimide-functional methacrylate-based polymer backbones. These dynamic networks decross-link and flow like viscous liquids under melt blowing conditions, then revert to a network via cooling-induced cross-linking during/after melt blowing. Finally, the resulting cross-linked fibers can be recycled because of their reversible dynamic nature, which may help address the microfiber pollution problem. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P30.00009: Carefully Controlled Photo-catalyzed Thiol-ene Networks of Poly(lactic acid) Nicholas Baksh, Ryan Toomey, Nathan Gallant PLA is researched for TE scaffolds, drug delivery, implants, and environmentally safe plastics. Bulk PLA has a tensile and flexural modulus of 3.5 and 6 GPa respectively and a Rockwell hardness of 88; thus despite bioabsorbable advantages, it is weak compared to metal implants. Additionally, a uniform degradation rate, which needs to be tuned to match tissue growth and regulate drug delivery, requires minimal molecular variability. Crosslinkable PLA would not only improve mechanical properties, but offer tunability via crosslink density. Further, catalysis by cell safe light and orthogonality of crosslinkable groups allow in-vivo crosslinking, minimizing implant procedures. Bis alpha, omega –ene functionalized PLA oligomers for use with thiolene chemistry were synthesized with polydispersities around 1.3 using organic catalysts. Ordered networks were photo-catalyzed with a multi-arm thiol. End functionalities allow crosslink density to be controlled by oligomer length, and the ordered network minimizes molecular variabiliy. Crosslinked samples prepared with the same oligomer consistenly show identical characterizations as analyzed by DSC, NMR, FTIR, and nano-indentation. Lastly, stress-strain curves exhibited a singular linear elastic regime. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P30.00010: Characterizing Network Structure and Protein Separation in Lignin-Based Hydrogel Composites Nicholas Gregorich, Junhuan Ding, Mark C Thies, Eric Davis Lignin-based hydrogels have recently garnered attention for use in a variety of biological applications involving proteins such as protein separation and delivery as lignin is a sustainable, naturally abundant biopolymer. However, to date, the use of these materials in protein related applications has been hindered by our limited understanding of how the addition of lignin, both as a crosslinker and ‘passive’ filler, affects the network (pore) structure of the crosslinked hydrogel. In this study, lignin-poly(vinyl alcohol) composites were synthesized using lignin of controlled, narrow molecular weights (MWs), allowing for the fabrication of membranes with more homogeneous network structures. The permeability of different proteins through the hydrated composites was measured via ultraviolet-visible spectroscopy, where protein permeability was found to depend on the MW and end group functionality of the lignin. In addition, poroelastic relaxation indentation was used to characterize both the mechanical (elastic modulus) and transport properties (diffusivity, effective pore size) of the composites. Results from this study illustrate how the incorporation of well-defined lignin into hydrogel composites can be used to directly tune the properties of the resultant membrane. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P30.00011: Modeling reconstituted silk fibroin gels during deformation Peter Olmsted, Peiran Jin Silk from silkworms has been used in the textile industry for thousands of years. It consists of β-sheet structures formed from hydrophobic domains in the protein fibroin. Recently, a physical electrogel (e-gel) was made by reconstituting Bombyx mori silk into stable aqueous solutions and then applying small DC electric field [Tabatabai et al, Soft Matter 11 (2015) 756]. The e-gels exhibit distinctive strain hardening and are partially recoverable from strain. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P30.00012: Overcoming the Achilles' Heel of Dynamic Vitrimer Networks: Modification and Application of Flory-Stockmayer Theory to Minimize Creep Lingqiao Li, John Torkelson Vitrimers are a promising class of dynamic polymer networks, but they have an Achilles’ heel: above Tg, vitrimers exhibit significant creep under conditions where permanently cross-linked networks exhibit little or no creep. Vitrimers can be designed with strongly suppressed creep and excellent reprocessability by incorporating a subcritical fraction of permanent cross-links. This fraction of permanent cross-links, which has little or no effect on reprocessability, is defined by the gelation point of only permanent cross-links leading to a percolated permanent network. Modifying Flory–Stockmayer theory, we developed a simple theory that predicts an approximate limiting fraction. To test our theory, we designed vitrimers with controlled fractions of permanent cross-links. Our experiments support our theoretical prediction: when the fraction of permanent cross-links is subcritical, the vitrimer can be reprocessed with full recovery of cross-link density. In particular, with a predicted limiting fraction of 50 mol %, a vitrimer system designed with 40 mol % permanent cross-links achieved full property recovery associated with cross-link density after reprocessing and ~70% creep reduction relative to a similar vitrimer without permanent cross-links. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P30.00013: Defects as a Highway to Stress Relaxation of Vitrimers Simone Ciarella, Francesco Sciortino, Wouter Ellenbroek Vitrimers are a promising class of plastics made by disordered networks of polymers. They are an ideal recyclable material being both strong and malleable, because unlike common plastics, vitrimers can swap their bonds without breaking. The swap mechanism also grants them exceptionally versatile properties ranging from self-healing to responsiveness to chemical and physical stimuli. Understanding how the mechanics of vitrimers follow from such bond-swap dynamics is a key physical question that we address using a new coarse-grained MD model which captures the essence of the bond dynamics while being insensitive to other chemical details. Our results reveal a dramatic dependence of their malleability on the number of polymer chains that loop back onto themselves. This highlights the importance of choosing the right building blocks for these new materials, as choices concerning polymer architecture have immediate implications for the number of such loops. Our work thus provides new guidelines for designing and developing these remarkable plastics. [1] Ciarella et al., PRL 2018. |
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