Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D15: Polymer Gels |
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Sponsoring Units: DPOLY Chair: Gabriel Sanoja, The University of Texas at Austin Room: Room 207 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D15.00001: Effects of microstructure on the stretchability and retractability of a multicomponent hydrogel Santanu Kundu, Anandavalli Varadarajan Elastic biopolymers such as resilin display remarkable mechanical properties, including high stretchability and resilience, which many species exploit in nature for mechanical energy storage to facilitate their movement. Such properties of resilin have been attributed to its balanced combination of hydrophilic and hydrophobic segments. We have synthesized gels with both hydrophilic and hydrophobic components, and we will present the effect of gel microstructure, particularly that of hydrophobic components, on their mechanical properties. Hydrogels composed of acrylic acid (AAc), alkyl-acrylamide, for example, methacrylamide (MAM), butyl acrylamide (BAM), and poly(propylene glycol diacrylate) (PPGDA) were synthesized using a free radical polymerization. Gels with MAM and varying concentrations of PPGDA displayed increasing elastic moduli with PPGDA concentration. When released from a stretched state, these gels retracted rapidly, and the retraction velocity also increased with PPGDA concentration. PPGDA is slightly hydrophobic, but additional hydrophobic domains in the gels were incorporated by replacing MAM with hydrophobic BAM. The effects of increased hydrophobicity on the tensile properties, retraction velocity and acceleration will be presented. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D15.00002: Influence of Spatial and Topological Heterogeneities on Gel Point and Network Structure Antonia Statt Polymer networks are widely used for applications varying from drug delivery, soft robotics, tissue engineering, to commodity materials. The formation of the network and its transition from a fluid to an elastic solid at the gelation point can be predicted theoretically, however, the effect of spatial and topological heterogeneities on the gel point and the resulting network structure is less understood. We use different methods to generate model networks of crosslinked polymer chains in silico. All networks have the same number of end-functionalized chains and crosslinkers with functionality 4, mimicking tetra-PEG hydrogels. Once formed, we investigate their structure and gel point as function of spatial distribution of crosslinkers and topological defects in the network. We find that inhomogeneous crosslinker distributions and overall increased density have a similar effect and lead to a reduction of primary loops in the network. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D15.00003: Investigating the relationships between composition, processing, and mechanics in PEGDA-PEGMEA hydrogels Yongkui Tang, Michal Levin, Olivia G Long, Claus D Eisenbach, Noy Cohen, Megan T Valentine Poly(ethylene glycol) diacrylate (PEGDA) hydrogels have been widely used in biomedical applications because they are biocompatible and can be easily fabricated via photocrosslinking. To meet various application needs, it is crucial to precisely control the mechanical properties of PEGDA hydrogels. However, this is a challenging task due to the structural heterogeneity of PEGDA hydrogel networks, as classical theories developed for different polymer network types are not suited to provide accurate predictions. In this work, we systematically study a series of hydrogels based on PEGDA and monofunctional poly(ethylene) methyl ether acrylate (PEGMEA) with different molecular weights and precursor weight fractions, while maintaining a constant mole ratio between the two monomers. Based on uniaxial compression and swelling data, in combination with our understanding of network topology from analysis of polymerization kinetics, we develop a model that relates molecular characteristics of network components and processing parameters to the mechanical properties of PEGDA-based hydrogels. The potential of the new model for tailoring the hydrogel's mechanical properties will be discussed. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D15.00004: Increasing the poroelastic diffusion coefficient in hydrogels Yiwei Gao, H. Jeremy J Cho Hydrogel-based atmospheric water harvesting systems have gained popularity in recent years due to the increasing global water scarcity. In such applications, the speed of water transport can dictate water harvesting performance. As such, it is important to understand how liquids permeate through hydrogels. Hydrogels are soft and swellable polymeric networks where water transport is described by the poroelastic diffusion coefficient—a combined permeability-stiffness property of hydrogels. Our study uncovers a simple scaling relationship between the hydraulic permeability and mechanical stiffness of hydrogels that applies to hydrogels that differ only by crosslinking. Through the prefactors of the scaling relationship, we provide insight on how to improve the poroelastic diffusion coefficient, paving the way for improved gels for water harvesting. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D15.00005: Relaxation Dynamics in Complex Coacervate Core Hydrogels: Charge Block Length Asymmetry MoonChul Ryu Complex coacervate core hydrogels(C3Hs) are formed by mixing ABA triblock copolymer and oppositely charged A' counterparts, where complex coacervate core are bridged by hydrophilic B blocks in aqueous media. C3Hs have great potentials for sustained release drug delivery and additive manufacturing which is attributable to regulated hydrogel relaxation dynamics. In this study, we investigate the effect of chain length asymmetry on the hydrogel relaxation dynamics using dynamic mechanical analysis. C3Hs were prepared by mixing of ABA triblock copolymer and oppositely charged A'B diblock copolymer in salty water, which can distinguish the role of each charged polymers. We obtained that the relaxation times of C3Hs were considerably controlled by the average charge block length of two block copolyelectrolytes. Also, the radii of coacervate cores are reasonably regulated by the entropic penalty of core block stretching. The results are discussed in terms of the relaxation dynamics with current understanding of self-assembled triblock copolymer hydrogels. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D15.00006: Cluster number and size distributions near the gel point Douglas Li The number and size distributions of finite clusters formed near the gel point, which underlie the scaling behaviors of structural and mechanical properties of developing networks, are susceptible to the degree of gelation. Flory-Stockmayer theory and percolation theory predict two distinct sets of scaling behaviors, with mean-field and critical exponents respectively. The crossover between the two behaviors was argued by de Gennes to depend on the -1/3 power of the molecular weight of the precursor chain, which was supported by earlier experimental evidence. Here, we present the cluster statistics simulated with a hybrid MC/MD model, over a wide range of molecular weights, all falling into the narrow gelation window. The cluster number distributions confirm a power law decay, with a well-defined cutoff. The cluster sizes from different precursor chains were collapsed upon proper scaling based on the critical packing arguments, which reveals a broad and gradual transition between the mean-field and critical scalings. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D15.00007: Unveiling the effects of molecular topology on the flow property of entangled polymers under gelation Weizhong Zou, Keith E Husted, Jeremiah A Johnson, Bradley D Olsen As the applications for crosslinked polymers continue to expand, understanding the evolution of their microstructures becomes imperative to produce materials with the desired physical and mechanical properties for the application. Here, on the basis of ring opening polymerization, statistical copolymers are synthesized with the distribution of crosslinkable sites of NHS (n-hydroxysuccinimide) ester along the linear norbornene backbone. Through the controlled NHS ester amine reactions, side-linking model networks with tunable crosslinking density are achieved by varying the stochiometric ratio of mono-amines to diamines. These model networks are crosslinked in dilute solutions but characterized in neat with the corresponding architecture and rheological properties investigated by our recently developed "reaction-topology-viscoelastic" model. Compared to typical network of end-linking chemistry, a much higher fraction of loop-like structures is found for the above network structure. For a serial of side-linking model networks crosslinked under different concentrations, a nearly unchanged linear rheology indicates these high-loop-containing molecules behaves similarly in entangled regime as those of elastic network strands over the frequency window of interest. A further analogy to radical induced crosslinking of polyolefin melts on the characteristics of network defects as well as the rheology reveals two different gelation mechanisms indicating the great importance of molecular topology and the associated synthesis conditions on the properties of thermoset and gels. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D15.00008: Universal phase behavior of reversible polymer gels under mean field theory Daniel L Vigil, Kris T Delaney, Glenn H Fredrickson We present a new field-based model of reversible polymer gels in solution that utilizes recently developed Coherent States (CS) approaches. We are able to predict both phase separation boundaries and percolation transitions by invoking a mean field approximation and show that a small set of dimensionless parameters control the phase behavior. Gaussian fluctuation analysis beyond the mean field approximation accounts for network defects including loops, but makes unphysical predictions in the dilute supernatant. Fully fluctuating Field Theoretic Simulations (FTSs) on the other hand give physically meaningful corrections to the mean field results. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D15.00009: Swelling and Residual Bond Orientations of Polymer Model Gels: The Entanglement-Free Limit Michael Lang, Reinhard Scholz, Lucas Löser, Carolin Bunk, Nora Fribiczer, Sebastian Seiffert, Frank Böhme, Kay Saalwaechter We investigate the swelling of polymer model networks prepared at different polymer volume fractions and in solvents of different quality. We extend the existing theory to describe residual bond orientations (the vector and the tensor order parameters) for theta, good, and athermal solvents and put these relations in context with modulus at preparation conditions and the equilibrium degree of swelling. We find good agreement with the assumption of affine swelling for the weakly entangled networks of our study. The same scaling relations (up to numerical coefficients) are obtained for the vector order parameter, m, and the tensor order parameter, S, as a function of the preparation conditions, network structure, the equilibrium degree of swelling, Q, and the modulus at swelling equilibrium, G. We obtain m ∝ Q–2 and G ∝ m3/2 for swelling in theta solvents and m ∝ Q–1.08 with G ∝ m2.14 in the good-solvent regime, in both cases independent of preparation conditions. Modulus and residual bond orientation are related by G ∝ φ0m and G ∝ φ01.23m as a function of the preparation polymer volume fraction φ0 for theta solvents and good solvents, respectively. Computer simulations and experimental data for the good-solvent regime show good agreement with the predictions.
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Monday, March 6, 2023 4:48PM - 5:00PM |
D15.00010: Imaging Gel Networks by In Situ Transmission Electron Microscopy David Hoagland, Satyam Srivastava, Alexander E Ribbe, Thomas P Russell Visualizing polymer gel networks at the nanoscale remains an immense challenge. Transmission electron microscopy (TEM) can be performed on chemically and cryogenically stabilized gels, but either approach is prone to artefacts, and solvent immobilization puts dynamics of solutes, as well as of the network itself, out of reach. Here, TEM is explored for imaging gels solvated by ionic liquids, which due to nonvolatility, are stable in vacuum. Physical gels are created by frustrated crystallization of polymer solutions supersaturated by cooling. Beneficially, these gels are rigid, suppressing local structural fluctuations, and due to crystallinity, offer additional diffraction contrast. A model system is polyethylene glycol solvated by the ionic liquid ethylmethylimidazolium ethylsulfate [EMIM][EtSO4]; solutions of modest concentration gel across the openings of a TEM grid as temperature falls below the polymer's melting temperature. Imaging reveals a heterogeneous network with features from 5 to 200 nm, consistent with small angle x-ray data. The crystalline polymer forms high contrast linear struts that are interconnected by lower contrast amorphous polymer. A 3D representation of the network is gained by electron tomography. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D15.00011: The Effects of Small Molecule Acids on PAAMPSA/PANI Systems Colton L Duprey As biological sensing and monitoring increase in popularity, it becomes evident |
Monday, March 6, 2023 5:12PM - 5:24PM |
D15.00012: Surface Gel Dynamics. Sujata Dhakal, Svetlana Morozova Gel systems have a complex surface topology that can easily deform. Understanding of gel interactions at surfaces is necessary for applications like medical sutures, underwater adhesion, contact lenses, etc. Light scattering techniques have been used to study the dynamics of gel systems in the bulk but, little is known about the interaction of these gel systems at surfaces. Here, we use Differential Dynamic Microscopy (DDM) paired with Confocal imaging and Dynamic Light Scattering (DLS) to study the network motion of Poly Vinyl Alcohol (PVA) gels and Hyaluronic Acid (HA) gels at heights ranging from 0 – 1000 nm away from a surface. Dynamics of gels with different cross-link densities are compared, and bulk measurements are confirmed with DLS. The confocal imaging paired with DDM gives an accurate sense of the location of the gel surface, its texture, and dynamics. We observe that gel network motion increases as we move from the surface to the bulk, concluding that the surface interaction changes local dynamics. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D15.00013: Understanding the Fundamental Mechanism of Solute Diffusion in Block Copolymer Organogels Kenneth P Mineart In recent years, organogels composed of a styrenic triblock copolymer and aliphatic mineral oil have been considered as potential candidates for transdermal drug delivery materials wherein they could serve as a pharmaceutical reservoir and pressure-sensitive adhesive. Work in this area so far has been a quest to match the performance of commercially-available products by varying gel formulation. This trial-and-error approach is inefficient and a bottom-up methodology based upon fundamental science would be superior. Our goal is to understand the underlying mechanism of solute diffusion in styrenic triblock copolymer organogels to address this deficiency. To do so, we have measured solute diffusivity values in gels across a number of factors including copolymer concentration, copolymer molecular weight, and solute size. Following a brief overview on how diffusivity values were determined, this presentation will interpret their trends using solute-in-gel diffusion theory. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D15.00014: Structural relaxation of dynamic formation of clustering within a extracellular matrix, a simulation model of articular cartilage Alexandros Chremos, Jack F Douglas, Peter J Basser, Ferenc Horkay
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Monday, March 6, 2023 5:48PM - 6:00PM |
D15.00015: Gelation and Multiple Macrophase Transitions in Dilute Aqueous Solutions of Nanoscale Hydrophilic Macroions Xiaohan Xu, Yuqing Yang, Yifan Zhou, Kexing Xiao, Jennifer Szymanowski, Ginger E Sigmon, Peter C Burns, Tianbo Liu Nanoscale (1-5 nm) hydrophilic macroions demonstrate different solution behaviors in polar solvents from simple ions or colloidal suspensions. We observe a series of macrophase transitions in their dilute aqueous solutions (as low as 0.5 mM) involving solution, gel, coacervate and precipitation phases in the presence of di- or trivalent cations (Y3+, Sr2+…), by using two uranyl peroxide (U6060- and U24Pp1248-) molecular clusters as models, suggesting that soluble ions could possess unexpected rich phasal behaviors. The gelation mechanism could be attributed to the size disparity between macroions and counterions, the consequent moderate counterion association around macroions and then tunable counterion-mediated attraction. In many cases, 2-D nanosheets are formed, followed by enclosing into self-assembled hollow, spherical, single-layered blackberry-type structures with sizes accurately tunable depending on the strength of the attraction. Gelation is the result of very tough nanosheets formed by strong counterions which cannot easily bend therefore staying as large, open structures in solution. The dilute macroion solution will first transfer into hydrogels and then turn into coacervates with increasing multivalent cation concentration. We will discuss the critical requirements of such interesting phase transitions and the common features of these unique phase behaviors of macroion solutions, as well as the rheological and thermodynamical features of the gels. |
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