Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C59: Gels and NetworksInvited
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Sponsoring Units: DPOLY Chair: Jan Genzer, North Carolina State Univ Room: LACC Petree Hall D |
Monday, March 5, 2018 2:30PM - 3:06PM |
C59.00001: Adaptable hydrogels with secondary reinforcement for regenerative medicine Invited Speaker: Sarah Heilshorn While injectable hydrogels are able to be delivered in a minimally invasive way, they typically rely either on polymerization in situ, which is difficult to control in a surgical setting, or are designed to be shear-thinning, which results in mechanically weak gels with fast erosion rates. To address these limitations, we have designed several injectable double-network hydrogels that undergo two stages of crosslinking: the first stage provides cell protection during injection and rapid hydrogel self-healing, while the second stage reinforces the hydrogel in situ to minimize erosion and to provide a dynamic range of tunable mechanical properties. These novel, double-network hydrogels combine the advantages of traditional physical and covalent crosslinking and have a wide tuning range of storage moduli (~ 50 to 5,000 Pa below 5 wt% polymer). Several different types of crosslinking strategies and engineered biopolymers have been employed in these designs, which allows for customization for a variety of injectable, minimally invasive, regenerative medicine applications. |
Monday, March 5, 2018 3:06PM - 3:42PM |
C59.00002: Nonlinear Elasticity and Diffusio-Mechanical Coupling of Elastomeric Polymer Networks Reveald by Multiaxial Stretching Invited Speaker: Kenji Urayama General biaxial stretching with varying the strains independently in the two orthogonal directions covers a wide range of accessible deformation for incompressible materials such as gels and elastomers. A custom-built biaxial tester enables us to characterize the nonlinear elasticity of novel polymer gels including the Tetra-PEG gels with uniform network structure, the slide-ring gels with movable cross-links along the network strands, and the T-PEG double network gels showing the pronounced upturn of stress at high elongation. General biaxial stretching experiments are also employed to characterize the pronounced stress-softening in filled elastomers (Mullins effect). We also demonstrate that the volume change and the accompanying force reduction driven by imposed strain for fully swollen gels considerably depend on the degree of strain as well as the type of stretching. |
Monday, March 5, 2018 3:42PM - 4:18PM |
C59.00003: Externally regulated switching of topology in polymer metal-organic cage gels Invited Speaker: Yuwei Gu Recently, the merger of polymer networks comprised of flexible polymer chains with comparably rigid metal-organic assemblies, such as metal-organic cages/polyhedra (MOCs) and metal-organic frameworks (MOFs), has received extensive attention. In principle, such materials could combine the advantageous properties of each of these classes of networks. We have studied the properties of polymer networks comprised of telechelic macromers end-functionalized with ligands that form M2L4, M3L6, M12L24, and M24L48 MOCs. Addition of Pd2+ to these macromers produces constitutionally isomeric |
Monday, March 5, 2018 4:18PM - 4:54PM |
C59.00004: Dynamic precursors of failure in the creep of a colloidal gel Invited Speaker: Luca Cipelletti Material failure is ubiquitous, with implications from geology to everyday life and material science. It often involves sudden, unpredictable events, with little or no macroscopically detectable precursors. A deeper understanding of the microscopic mechanisms eventually leading to failure is clearly required, but experiments remain scarce. Here, we show that the microscopic dynamics of a colloidal gel, a model network-forming system, exhibit dramatic changes that precede its macroscopic failure by thousands of seconds. Using an original setup coupling light scattering and rheology, we simultaneously measure the macroscopic deformation and the microscopic dynamics of the gel, while applying a constant shear stress. We show that the network failure is preceded by qualitative and quantitative changes of the dynamics, from reversible particle displacements to a burst of irreversible plastic rearrangements. |
Monday, March 5, 2018 4:54PM - 5:30PM |
C59.00005: Stress relaxation and anomalous diffusion in unentangled supramolecular networks Invited Speaker: Jorge Ramirez Supramolecular networks are a class of soft materials with applications in matrices for tissue engineering, enhanced oil recovery, sacrificial components in tough double networks, injectable biomaterials for minimally invasive surgery and self-healing soft materials. In most of these applications it is crucial to understand the mechanical properties of the materials and predict the diffusion of the network forming constituents. Recent experiments have revealed that a variety of unentangled associative polymers with different architecture (linear and branched) and different nature of the associating interaction (associative protein domains and metal-ligand bonds) exhibit unexplained apparent superdiffusive behavior. Here, results of a coarse-grained molecular model of star-shaped unentangled associating polymers are presented. The model explains the observed superdiffusive scaling and reveals three basic mechanisms of molecular diffusion: caging dynamics, walking diffusion and molecular hopping, all of which depend strongly on polymer concentration, arm length, and the association/dissociation kinetics. The observed superdiffusive behavior results primarily from molecular hopping, which prevails over walking when the kinetics of attachment are much slower than the relaxation time of dangling strands. Simple scaling relationships are derived to identify the range of rate constants over which this behavior can be expected. The formation of intramolecular associations or loops in the network promotes this superdiffusive scaling by reducing the total number of arms that must detach in order for a hopping event to occur. In addition, the effect of the number of arms on the diffusivity and relaxation modulus is also studied, the model is extended to different architectures, and the impact of the model predictions on practical aspects like the gel erosion of self-healing time are explored. |
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